JP2002344015A - Nitride semiconductor light emitting device - Google Patents

Abstract

(57) [Problem] To provide a nitride semiconductor device having high external quantum efficiency in a large current region and capable of performing surface emission. SOLUTION: At least a nitride semiconductor light emitting device comprising a gallium nitride-based compound semiconductor layer having a structure in which a light emitting layer is sandwiched between a p-type cladding layer and an n-type cladding layer having a smaller refractive index than the light emitting layer. The end face of the light emitting layer is inclined at an angle of more than 45 degrees and less than 90 degrees with respect to the lamination surface of the semiconductor layer, wherein the nitride semiconductor light emitting device is characterized in that:

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting diode (LED), a laser diode (LD), a solar cell,
Nitride semiconductors (In _X Al _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, X + Y ≦ used in light emitting elements such as optical sensors or electronic devices such as transistors and power devices
The present invention relates to a light emitting device comprising 1).

[0002]

2. Description of the Related Art Today, nitride semiconductors have already been put into practical use as various types of light sources, such as full-color LED displays, traffic lights, and image scanner light sources, as high-intensity pure green light-emitting LEDs and blue LEDs. For example, Japanese Patent Laid-Open No. 9-1
No. 53,642 discloses a GaN buffer layer, a Si-doped n-type GaN layer, an undoped InGaN light-emitting layer, and a Mg-doped p-type A on a sapphire substrate.
A light emitting diode comprising an lGaN layer and a Mg-doped p-type GaN layer is described.

[0003]

However, at present, there is a demand for a light source for illumination instead of a fluorescent lamp, and the light emitting diode as described above does not have a sufficient output amount, and further improvement is required. ing.

Accordingly, the present invention provides a nitride semiconductor light emitting device capable of emitting high power and emitting surface light.

[0005]

That is, a nitride semiconductor light emitting device according to the present invention has a structure in which at least a light emitting layer is sandwiched between a p-type clad layer and an n-type clad layer having a smaller refractive index than the light-emitting layer. A nitride semiconductor light-emitting device comprising a gallium nitride-based compound semiconductor layer having:
It is characterized by being inclined at an angle larger than 90 degrees and smaller than 90 degrees. As a result, a nitride semiconductor light-emitting device that has good external quantum efficiency and emits light in a planar manner as the current region increases is obtained.

A p-type contact layer is provided on the p-type cladding layer, and a p-side ohmic electrode having a thickness of 5000 ° or more is provided on almost the entire surface of the p-type contact layer. Accordingly, a nitride semiconductor light emitting device that can maintain good reliability even when a large current is dropped and can uniformly emit light with a high output from a direction opposite to the p-side ohmic electrode on one surface is provided. can get. In particular, it is preferable that the p-side ohmic electrode is formed over 80% or more of the upper surface of the p-type contact.

The p-side ohmic electrode is a multilayer film having a metal oxide layer. Thereby, the ohmic properties of the p-side ohmic electrode and the p-type contact layer are improved, and a nitride semiconductor light emitting device capable of emitting light with higher output in a large current region is obtained.

It is preferable that a reflective film is provided in contact with the end face of the light emitting layer, so that light emitted from the end face can be efficiently guided toward the light emitting surface and the light emitting region.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventor of the present invention
In the gallium nitride-based compound semiconductor light emitting device, by adjusting the angle of the cavity end face, which is the end face of the light emitting layer,
The inventors have found that it is possible to improve the external quantum efficiency in a large current region, and have accomplished the present invention.

A light emitting diode device using a nitride semiconductor is a surface-emitting type light emitting device, but emits light only by spontaneous emission, and does not increase the light emission transition probability.
The amount of injected current and the amount of light output are in a linear relationship until they are thermally saturated, and when a certain amount of current is reached, the light output becomes saturated. For this reason, under a large current region, the luminous efficiency may be reduced by the influence of heat but does not increase, and it is not possible to obtain sufficient light output from the light emitting diode element to be used as a light source for illumination. It was difficult.

Further, a semiconductor laser device using a nitride semiconductor is considered to be capable of oscillating in a wide range of visible light from ultraviolet to red, and its application range is not limited to the light source of the optical disk system. , Laser printers, optical networks and other light sources are expected to be diverse. In addition, the present applicant has announced a laser exceeding 10,000 hours under the condition of continuous oscillation of 405 nm, room temperature, and 5 mW. In particular, when the light-emitting layer has a structure sandwiched between the upper and lower cladding layers, by reducing the refractive index of both cladding layers and increasing the refractive index in the waveguide sandwiched between the upper and lower cladding layers, Light is efficiently confined in the waveguide, and as a result, contributes to a reduction in threshold current density in the laser device. Such a semiconductor laser uses light emitted by spontaneous emission as incident light,
Light can be amplified and stimulated emitted. Therefore, a high output can be obtained in a large current region.

However, the laser device having the above configuration has
Emit small spot size light from the end face,
Since the light emission characteristics in one direction were too strong, it was unsuitable as a light source for illumination.

Therefore, the present invention utilizes the above-mentioned laser element structure to disperse the light emitted from the end face of the light emitting layer into the incident light for stimulated emission and the externally extracted light to the light emitting surface side, thereby providing a large current region. To provide a nitride semiconductor light emitting device having high external quantum efficiency.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. As shown in FIG. 1, the nitride semiconductor light emitting device of the present embodiment has, for example, a p-type clad layer having at least a light emitting layer having a smaller refractive index than the light emitting layer on almost the entire surface of one of the sapphire translucent substrates. n
A gallium nitride-based compound semiconductor layer having a waveguide structure sandwiched by a mold cladding layer is laminated. The n-type contact layer is exposed by etching or the like from the p-type layer side in the peripheral portion, leaving the central portion of such a semiconductor layer. Here, in the present invention, the end face of the semiconductor layer exposed by the etching or the like is 6
It is inclined from 0 degree to less than 90 degrees. At the center of the semiconductor layer, a p-side ohmic electrode having a thickness of 5000 ° or more is formed on almost the entire surface of the p-type contact layer laminated on the uppermost surface. On the other hand, n is exposed on the exposed n-type contact layer so as to surround the p-side ohmic electrode.
A side ohmic electrode is formed. Hereinafter, each configuration of the present embodiment will be described in detail.

As the nitride semiconductor used in the nitride semiconductor device of the present invention, GaN, AlN, or InN, or a gallium nitride-based compound semiconductor (I
_{n x Al y Ga 1-xy} N, 0 ≦ x, 0 ≦ y, x + y ≦ 1)
There is. In addition, a mixed crystal in which a part of the gallium nitride-based compound semiconductor is substituted with B and P may be used. In addition, a nitride semiconductor containing In used for a light emitting layer, a well layer, a barrier layer, or the like is specifically In _x Al _y Ga _1-xy N (0 <
x, 0 ≦ y, x + y ≦ 1). Further, as a nitride semiconductor containing Al, specifically, In _x Al _y Ga _1-xy N (0 ≦ x, 0
<Y, x + y ≦ 1) is to use a nitride semiconductor. (Light Emitting Layer) In the nitride semiconductor device of the present invention,
The exposed end surface of the light emitting layer is inclined with respect to the lamination surface of the semiconductor layer, and the inclination angle is an angle larger than 45 degrees and smaller than 90 degrees, more preferably 60 degrees or more and less than 90 degrees. is there. Thereby, the light spontaneously emitted in the light emitting layer is totally reflected by the end face, and is dispersed into the incident light for the stimulated emission and the light emitted to the substrate side which becomes the light emitting surface. As described above, by realizing a light emitting state having both stimulated emission and spontaneous emission, a nitride semiconductor light emitting device that can have higher external quantum efficiency as the current becomes larger is obtained. By tilting the end face as described above, the outgoing light is emitted in a direction forming an acute angle with respect to the lamination surface. As a result, a wide radiation angle can be obtained, and uniform surface light emission can be achieved.

On the other hand, when the inclination angle is 45 degrees or less,
Outgoing light at 90 degrees or more with respect to the laminated surface
It is reflected in the direction. As a result, the outgoing light is emitted from the outer peripheral
And the center becomes dark, and uniform light emission cannot be obtained.
In addition, when the inclination angle is 90 degrees, the stimulated emission is excellent.
But light with a small spot is emitted from the end face
It is difficult to take out light in a plane from the stacking direction.
It is difficult. When the inclination angle is an obtuse angle, the emitted light is
The light is emitted to the pole forming surface side. In the present invention, a large current
The purpose and the electricity used to make this possible
The poles have low light transmittance and are considered to reflect light. This
In the case of, the light totally reflected at the end face of the light emitting layer is
After reflection, it can be taken out from the side opposite to the electrode surface.
It is possible, but light is absorbed in the layer and high output is obtained.
Absent. Also, light is to be extracted from the electrode forming surface side.
Then, it is necessary to form the p-side electrode with a small film thickness to make it light-transmitting.
is there. However, an electrode having a small film thickness has an electric resistance.
Due to the high resistance, heat is generated in the electrode part, and the electrode itself
High heat absorption. Therefore, when a large current is dropped,
It is very difficult to maintain the reliability of the child. The present invention
Compound semiconductor light-emitting device, the end face of the exposed light-emitting layer is laminated
Tilt to an angle greater than 45 degrees and less than 90 degrees
By tilting it, the surface opposite to the electrode
High reliability even in the current range, uniform with high output
It can emit surface light. Further, the light emitting layer
On the end face,_O, TiO₂, Al₂O₃, ZrO₂, N
b₂O ₅(Or NbO, NbO₂, Nb₂O₃) Etc.
If a reflective film is provided, it will reflect light efficiently and completely
This is preferable.

The light emitting layer has a nitride semiconductor containing at least In. Here, the composition of the nitride semiconductor containing In is not particularly limited, but a nitride semiconductor represented by In _x Ga ₁ -xN (0 <x ≦ 1) is preferably used. At this time, the In-containing nitride semiconductor may be non-doped, n-type doped, or p-type doped, but is preferably non-doped, undoped, or n-doped. By providing it inside, high output can be achieved in a nitride semiconductor device such as a laser device and a light emitting device. When the light emitting layer has a quantum well structure, the nitride semiconductor containing In is used for at least the well layer. Here, the quantum well structure may be either a multiple quantum well structure or a single quantum well structure. Preferably, by using a multiple quantum well structure, it is possible to improve the output, lower the oscillation threshold, and the like. As the quantum well structure of the light emitting layer, a structure in which a well layer and a barrier layer described later are stacked can be used. At this time, in the case of a quantum well structure, by setting the number of well layers to 1 or more and 4 or less, for example, in a laser element, it is possible to reduce the threshold current, and it is more preferable.
By using a multiple quantum well structure in which the number of well layers is two or three, a high-output laser device or light-emitting device tends to be obtained.

In the multiple quantum well structure, the number of barrier layers sandwiched between well layers is not limited to one (well layer / barrier layer / well layer), but may be two or more layers. The barrier layer of "well layer / barrier layer (1) / barrier layer (2)
/ Barrier layer (3) /.../ well layer ".
A plurality of barrier layers having different impurity amounts may be provided. For example, there is a structure in which an upper barrier layer made of a nitride semiconductor containing Al is provided on a well layer, and a lower barrier layer having a smaller energy band gap than the upper barrier layer is provided thereon. Specifically, by providing an upper barrier layer made of a nitride semiconductor containing Al disposed on the well layer, segregation of In and in-plane distribution of In concentration are induced in the well layer, and quantum dots, Since the quantum wire effect tends to be obtained, this may be used. At this time, as the nitride semiconductor containing Al, specifically, In _x Al _y Ga _1-xy N (0 ≦
x, 0 <y, x + y ≦ 1), preferably a ternary mixed crystal Al _z Ga _{1 -zN.}
The use of (0 <z ≦ 1) is preferable because the crystal can be grown with good crystallinity and controllability. Further, the nitride semiconductor containing Al is not limited to the upper barrier layer, and may be a lower barrier layer disposed below the well layer.
And (3) may be provided as a barrier layer (2). Preferably, it is used other than the lower barrier layer provided in contact with the lower part of the well layer, because the well layer tends to be formed with good crystallinity, and the above-described quantum effect tends to be easily obtained. Because there is. The lower barrier layer in contact with the bottom of the well layer, it is preferable to use a nitride semiconductor not containing _{Al, In x Ga 1 -x N} (0 ≦ x ≦ 1)
Is preferable from the viewpoint of the crystallinity of the well layer, and furthermore, the In semiconductor in which the In mixed crystal ratio x is larger than 0 is used.
GaN is preferable because the effect of the underlayer on the well layer can be obtained. (Well layer) As the well layer in the present invention, it is preferable to use a nitride semiconductor layer containing In. At this time, a specific composition is preferably In _α Ga _1-α N (0 <α ≦ 1). Can be used. This results in a well layer that enables good light emission and oscillation. At this time, the emission wavelength can be determined by the In mixed crystal ratio.

The thickness of the well layer and the number of the well layers can be arbitrarily determined. By setting the specific film thickness in the range of 10 ° to 300 °, preferably in the range of 20 ° to 200 °, Vf and the threshold current density can be reduced. In addition, from the viewpoint of crystal growth, if the thickness is 20 ° or more, a layer having relatively uniform film quality without large unevenness in film thickness can be obtained. It becomes possible. The number of well layers in the light emitting layer is not particularly limited, and is 1 or more. At this time, when the number of the well layers is 4 or more, the light emitting layer The overall film thickness increases, and Vf
Is increased, the thickness of the well layer is reduced to 100 Å.
It is preferable to keep the thickness of the light emitting layer low within the following range.

In the well layer of the present invention, In
Similarly to the nitride semiconductor containing, the n-type impurity may or may not be doped. However, the well layer is I
Since a nitride semiconductor containing n is used and the crystallinity tends to deteriorate when the n-type impurity concentration is increased, it is preferable to suppress the n-type impurity concentration to be low to form a well layer having good crystallinity. Specifically, in order to maximize the crystallinity, the well layer is grown undoped. At this time, the n-type impurity concentration is 5 × 10 ¹⁶ / cm ³ or less, which is substantially n-type. That is, the well layer does not contain impurities.
When the well layer is doped with an n-type impurity, if the n-type impurity concentration is 1 × 10 ¹⁸ / cm ³ or less and 5 × 10 ¹⁶ / cm ³ or more, the crystallinity is deteriorated. The threshold current density and Vf can be reduced while keeping the carrier concentration low and the carrier concentration high. At this time, since the n-type impurity concentration of the well layer is almost the same as or smaller than the n-type impurity concentration of the barrier layer, light emission recombination in the well layer is promoted, and the light emission output tends to be improved. preferable. At this time, the well layer and the barrier layer may be grown undoped to form a part of the light emitting layer.

In particular, when the device is driven by a large current (such as a high-output LD, a high-power LED, or a super-photoluminescence diode), the well layer is undoped.
By substantially not containing an n-type impurity, recombination of carriers in the well layer is promoted, and light-emitting recombination with high efficiency is realized. Conversely, when the n-type impurity is doped into the well layer,
Since the carrier concentration in the well layer is high, the probability of radiative recombination is rather reduced, and the drive current and the drive current are increased under a constant output, resulting in a vicious cycle, and the reliability of the device (device life).
Tend to decrease significantly. For this reason, in such a high-output device, the n-type impurity concentration of the well layer is set to at least 1 × 10 ¹⁸ / cm ³ or less, and preferably, the concentration of the undoped or substantially non-contained n-type impurity. By doing so, a nitride semiconductor device capable of high-output and stable driving can be obtained. Also, in the case of a laser element in which a well layer is doped with an n-type impurity, the spectral width of the peak wavelength of the laser light tends to be widened.
0 ¹⁸ / cm ³ , preferably 1 × 10 ¹⁷ / cm ³ or less. (Barrier layer) In the present invention, the composition of the barrier layer is not particularly limited, but the bandgap energy difference is provided between the barrier layer and the well layer so that the bandgap energy is larger than that of the well layer. A nitride semiconductor containing In or a nitride semiconductor containing GaN or Al having a lower In mixed crystal ratio can be used. As a specific composition, In _β Ga _1-β N (0 ≦ β <1, α>
_{β), GaN, Al γ Ga} 1-γ N (0 <γ ≦ 1) or the like can be used. Here, in the case of a barrier layer (lower barrier layer) serving as an underlayer in contact with the well layer, a nitride semiconductor containing no Al is preferably used. This is because a well layer made of a nitride semiconductor containing In is made of A such as AlGaN.
This is because, when grown directly on a nitride semiconductor containing l, the crystallinity tends to decrease, and the function of the well layer tends to deteriorate.

The barrier layer has a p-type impurity and an n-type impurity.
May be doped or non-doped
Is preferably doped with n-type impurities or non-doped.
Or undoped. this
When doping n-type impurities in the barrier layer,
At least 5 × 10¹⁶/cm^ThreeDoped over
That is. Specifically, for example, in the case of an LED
5 × 10¹⁶/cm ^ThreeMore than 2 × 10¹⁸/cm^ThreeThe following range
Having an n-type impurity in the surrounding area, and a higher output
LED and high power LD, 5 × 10¹⁷/cm^Threethat's all
1 × 10²⁰/cm^ThreeThe following range, preferably 1 × 10¹⁸/ C
m^Three5 × 10 or more¹⁹/cm^ThreeDoped in the following range
It is preferable to dope at such a high concentration.
Means that the well layer contains substantially no n-type impurity,
It is preferred to grow in a loop.

On the other hand, the outermost and most p
The barrier layer located on the mold layer side is preferably made substantially free of n-type impurities, so that carrier injection from the p-type layer becomes good and the element lifetime tends to be improved. This is presumably because the p-side barrier layer is provided in contact with the p-type layer, serves as an injection port for carriers from the p-type layer, and hinders the injection of carriers when it has an n-type impurity. It is considered that the carrier from the p-type layer is stably and efficiently injected into the well layer deeper, farther from the p-type layer and into the well layer by substantially not including the n-type impurity. Can be This is especially true for high-current driven, high-output LDs and LEs that inject large amounts of carriers with large currents.
D and the like tend to significantly improve the element life. At this time, when the n-type impurity does not substantially include the n-type impurity, the n-type impurity concentration of the p-side barrier layer is 5 × 1
0 ¹⁶ / cm ³ . Further, it is preferable that the most p-side barrier layer be formed on the outermost side in the light emitting layer. However, when the effect is reduced but not on the outermost side, for example, the well layer /
The effect can be expected even with a structure in which a barrier layer / well layer / p-type layer is stacked in this order. The position of the most p-side barrier layer is preferably located on the outermost side in the light emitting layer, and more preferably provided in contact with a p-side electron confinement layer described later, thereby confining electrons. This makes the injection of carriers from the p-type layer more efficient. Furthermore, since the p-side barrier layer has a p-type impurity, carriers from the p-type layer can be efficiently supplied to a well layer located further deep and a well layer located far from the p-type layer. It is preferable that the barrier layer is substantially free from n-type impurities and contains p-type impurities because it is implanted and the element lifetime tends to be further improved. At this time, the p-type impurity amount is 5
The range is from × 10 ¹⁶ / cm ^{3 to} 1 × 10 ²⁰ / cm ³ , preferably from 5 × 10 ¹⁶ / cm ^{3 to} 1 × 10 ¹⁸ / cm ³ . This is because even if the p-type impurity is increased to 1 × 10 ²⁰ / cm ³ or more, the carrier concentration hardly changes, so that the crystallinity is deteriorated due to the inclusion of the impurity, and the loss due to the light scattering action by the impurity is large. Instead, the luminous efficiency in the light emitting layer is reduced. Furthermore, 1 × 10 ¹⁸ / cm ³
When the content is less than the above, it is possible to suppress the decrease in the luminous efficiency due to the increase in the impurity, and to keep the carrier concentration from the p-type layer in the luminescent layer stably high. in addition,
As a lower limit of the p-type impurity, it is preferable that the p-type impurity has a slight amount of p-type impurity.
This is because the type impurities tend to function as carriers.

The thickness of the barrier layer is not particularly limited.
A range of 10 ° or more and 300 ° or less can be applied similarly to the well layer. (Waveguide structure) In the nitride semiconductor device of the present invention, at least the p-type clad layer in the p-type nitride semiconductor layer and the n-type in the n-type nitride semiconductor layer whose light-emitting layer has a smaller refractive index than the light-emitting layer. It is composed of a gallium nitride-based compound semiconductor layer having a structure sandwiched between clad layers. At this time, it is preferable to use a nitride semiconductor containing In for the light emitting layer, and it is preferable that the light emitting layer has an In mixed crystal ratio in which light emission with a wavelength of 400 nm or more can be obtained. Further, a light guide layer may be provided between the cladding layer and the light emitting layer so as to sandwich the light emitting layer. Here, in this specification, a region sandwiched between the p-type cladding layer and the n-type cladding layer is called a waveguide,
The above structure is called a waveguide structure. (Cladding Layer) As the n-type cladding layer and the p-type cladding layer, nitride semiconductors containing Al are preferably used, whereby a large difference in refractive index between the waveguide and both cladding layers can be obtained. it can. At this time, it is preferable that the nitride semiconductor of the cladding layer does not contain In, because the nitride semiconductor containing In tends to have lower crystallinity than the case not containing In. In a structure having a p-type cladding layer on a light-emitting layer, when a nitride semiconductor containing In is used for the p-type cladding layer, crystallinity is greatly deteriorated, and device characteristics are significantly deteriorated. At this time, specifically as a nitride semiconductor used for the cladding _{layer, Al b Ga 1-b N} (0 <b <1) is preferably used. (Light Guide Layer) An optical guide layer is provided between the clad layer and the light emitting layer. The light guide layer is important in forming a waveguide. This is because, in order to confine light in the waveguide, the refractive index of the cladding layer is relatively reduced as compared with the waveguide, and the refractive index difference is increased, or the refractive index in the waveguide is increased. However, when the wavelength of light from the light emitting layer is long, a difficult problem occurs. The reason is that the refractive index difference between AlGaN and InGaN has a large refractive index difference in a region where the wavelength is short, for example, around 400 nm, but the refractive index difference becomes smaller as the wavelength becomes longer. For this reason, the nitride semiconductor used for the cladding layer is made to have a higher Al alloy crystal ratio to reduce the refractive index of the cladding layer, or is required to have an I guide in the optical guide layer.
It is necessary to reduce the refractive index in the waveguide by using a nitride semiconductor containing n to increase the difference in the refractive index between the waveguide and the cladding layer. However, the cladding layer Al
When the mixed crystal ratio is increased, the crystallinity is greatly deteriorated, and there are also cracks and the like, which may cause a leak current and deteriorate the device characteristics.
It is difficult to provide a thick film and a nitride semiconductor having a high Al mixed crystal ratio in the element structure. Further, in a structure in which a nitride semiconductor containing In is used for a nitride semiconductor layer in a waveguide except for a light emitting layer, for example, an optical guide layer, and a refractive index of the waveguide is increased, the nitride semiconductor containing In is used. Light absorption occurs, which results in loss of light in the waveguide and deterioration of device characteristics such as an increase in threshold current.

Therefore, the waveguide sandwiched between the two cladding layers is provided with a first optical guide layer made of a nitride semiconductor containing In between the n-type cladding layer and the light emitting layer to provide a refraction in the waveguide. Is relatively large as compared with the cladding layer, and between the p-type cladding layer and the light-emitting layer, the second layer is formed of a nitride semiconductor containing no In (where the In mixed crystal ratio is 0). By providing the light guide layer, deterioration of crystallinity and light loss due to the nitride semiconductor containing In can be avoided, and a nitride semiconductor device having excellent device characteristics can be obtained. Hereinafter, each layer will be described. (First Light Guide Layer) The first light guide layer in the present invention is disposed between the light emitting layer and the n-type clad layer in the waveguide, and is made of a nitride semiconductor containing In. Here, the composition of the first light guide layer is preferably a nitride semiconductor not containing Al.
This makes it possible to increase the refractive index difference between the cladding layer using the nitride semiconductor containing Al, that is, to relatively increase the refractive index in the waveguide between the cladding layer and the waveguide sandwiched therebetween. And In _z G
By forming a nitride semiconductor represented by a _{1 -zN} (0 <z ≦ 1), a first light guide layer having good crystallinity can be obtained. Further, the first light guide layer and the light emitting layer or n
Between the mold clad layer, another layer may or may not be provided, that is, the first light guide layer may be provided in contact with the light-emitting layer or the n-type clad layer, or both,
It may be provided at one or both sides separately. Alternatively, a multilayer film structure in which a plurality of first light guide layers are stacked alternately with layers having different compositions from the first light guide layer may be used. Since the first light guide layer of the present invention is located between the light emitting layer and the n-type cladding layer and in the waveguide,
While functioning as a light guide layer, the inclusion of In increases the refractive index of the entire waveguide and contributes to confinement of light in the waveguide. Therefore, the second light guide layer on the p-type layer side It is considered that it also functions as a second light confinement layer as compared with

Further, the In mixed crystal ratio z of the first optical guide layer
Is the In mixed crystal ratio of the nitride semiconductor containing In in the light emitting layer,
Alternatively, in the case of a light emitting layer having a quantum well structure, the well layer In
Assuming that the mixed crystal ratio is w, it is preferable that z ≦ w, and it is more preferable that z <w. z <w
By being, the nitride semiconductor layer containing In in the well layer,
Alternatively, a large bad gap energy difference can be provided between the well layer and the first light guide layer, and the carrier injection efficiency can be improved. Furthermore,
When the first light guide layer is provided adjacent to the light emitting layer, the outermost light emitting layer in the light emitting layer is disposed closest to the n-type layer, and the barrier layer adjacent to the first light guide layer is provided. More preferably, the In mixed crystal ratio z of the first optical guide layer is set to satisfy z ≦ v as compared with the In mixed crystal ratio v of the barrier layer.
Further, it is preferable that z <v. When z ≦ v, a structure in which the bandgap energy gradually decreases near the junction between the light emitting layer 12 and the n-type layer 11 from the n-type layer to the light-emitting layer can be obtained. Carriers are efficiently injected from the n-type layer into the light emitting layer, and a more stepwise band gap structure can be obtained.

Here, referring to the above-described embodiments at the position of the first light guide layer, in the embodiment in which the first light guide layer is provided in contact with the light emitting layer and the n-type cladding layer, In
There is a tendency that it is difficult to form a nitride semiconductor containing a thick film with good crystallinity, so that when the waveguide is formed with a sufficient film thickness as a waveguide, the deterioration of the crystallinity causes the deterioration of device characteristics,
Conversely, if the film is formed with a thickness such that the crystallinity does not deteriorate the device characteristics, the film thickness becomes insufficient to function as a waveguide,
Device characteristics tend to deteriorate due to loss due to light leakage outside the cladding layer. When the first light guide layer is a multilayer film in which a plurality of layers are stacked between a light emitting layer and an n-type clad layer, for example, a superlattice structure is formed by stacking a large number of layers together with a nitride semiconductor not containing In. It is possible to form a thick film while suppressing deterioration of properties. For example, InGaN / Ga
A structure in which the composition is graded so that the In mixed crystal ratio increases as approaching the light emitting layer from the N multilayer film layer or the n-type cladding layer. On the other hand, in order to make the refractive index of the waveguide equal to that of a single film, the thickness of the multilayer film must be large and the first light guide layer containing In must be scattered in the multilayer film. Therefore, light loss due to In occurs in a multilayer film having a thickness larger than that of a single film, and the loss tends to be larger than that of a single film. In addition, as the position of the first light guide layer, various forms described above can be applied in the present invention, but it is preferable that the first light guide layer is disposed closer to the light emitting layer, more preferably in contact with the light emitting layer. . Although this is unknown in detail,
As shown in FIGS. 5 and 6 and the like, the band gap structure is made stepwise in a region from the n-type cladding layer to the light emitting layer,
It is considered that promoting the injection of carriers from the n-type layer side 11 has an effect.

Although the thickness of the first light guide layer is not particularly limited, it is preferably at least 1500 ° or less in consideration of the occurrence of light loss due to In as described above. Is 300 ° or more, it is possible to increase the refractive index of the entire waveguide and to form a large refractive index difference between the waveguide and the n-type cladding layer. Is formed.
At this time, as described later, since the function as the waveguide is affected by the total thickness of the region sandwiched between the cladding layer and the light emitting layer, the function of the region sandwiched between the n-type cladding layer and the light emitting layer is obtained. The first light guide layer is preferably determined in consideration of the total thickness. Further, as shown in FIGS. 5 and 6, when the first light guide layer is disposed adjacent to the barrier layer 2a closest to the n-type layer, the first light guide layer serves as a barrier layer. Since it is considered to contribute, the thickness of the first light guide layer in this case is good as a barrier layer and light confinement by setting the total thickness of the first light guide layer and the barrier layer 2a to 300 ° or more. It is preferable that the upper limit of the film thickness at this time is 1500 ° or less.

The first light guide layer may or may not be doped with an n-type impurity. Preferably, the first light guide layer is doped with an n-type impurity and has good n-type conductivity. It is. At this time, the first light guide layer is a nitride semiconductor containing In, and although not as large as a p-type impurity as described above, the first light guide layer is preferably deteriorated in crystallinity by doping with an n-type impurity. Is 1
When the content is in the range of × 10 ¹⁹ / cm ³ or less, deterioration of crystallinity in the nitride semiconductor containing In can be suppressed. (Second Light Guide Layer) The first light guide layer in the present invention is disposed between the p-type cladding layer and the light emitting layer in the waveguide, and is made of a nitride semiconductor having an In mixed crystal ratio of 0. Are preferred. This results in a layer having excellent crystallinity and functioning as a waveguide. This is because the structure in which the light emitting layer is sandwiched between the first light guide layer and the second light guide layer is provided in the waveguide, that is, the first light guide layer on the n-type layer side and the p
The second light guide layer on the mold layer side is opposed to the second light guide layer via the light emitting layer, and these are configured with different compositions, thereby forming an asymmetric waveguide structure having different functions in the waveguide. By setting the In mixed crystal ratio u of the nitride semiconductor used for the second optical guide layer to u = 0, a layer having excellent crystallinity can be formed, and an increase in Vf and threshold current due to deterioration in crystallinity can be avoided. it can. This is because the nitride semiconductor containing In
This is because the crystallinity tends to be worse than that containing no In. Also, unlike the first light guide layer, the second light guide layer needs to be doped with a p-type impurity to have p-type conductivity, and the impurity doping deteriorates the crystallinity. Mg, which is preferably used as an impurity, causes a significant deterioration in crystallinity, which is more remarkable in a nitride semiconductor containing In than in a nitride semiconductor not containing In.

In general, many nitride semiconductor devices such as LEDs and LDs have a structure in which an n-type layer, a light-emitting layer, and a p-type layer are stacked in this order.
An n-type layer disposed below a light-emitting layer using a nitride semiconductor containing In and a p-type layer disposed thereon generally have different growth conditions, and a p-type layer disposed above a light-emitting layer. The layer usually needs to be grown under a temperature condition that does not deteriorate crystallinity due to decomposition of In in the light emitting layer,
The n-type layer has no such limitation. For this reason, it may be difficult to grow a p-type layer grown at a low temperature under favorable crystal growth conditions.

The composition of the second optical guide layer is preferably a nitride semiconductor containing no In, more preferably a nitride semiconductor represented by Al _t Ga _{1 -tN} (0 ≦ t <1). Is used. At this time, in order to provide a refractive index difference from the p-type cladding layer, it is preferable to make the Al composition ratio t of the second nitride semiconductor smaller than the Al composition ratio of the p-type cladding layer. Furthermore, in consideration of the refractive index difference between the cladding layer and the waveguide, t ≦ 0.5, and with a low Al mixed crystal ratio, or in order to maximize the refractive index in the waveguide, Most preferably, GaN with t = 0 is used. The second light guide layer preferably has a p-type impurity. The second light guide layer contains a p-type impurity and has p-type conductivity, so that the second light guide layer can function as a p-type layer having good conductivity. At this time, the doping amount of the p-type impurity is not particularly limited. However, even if the nitride semiconductor does not contain In, the deterioration of the crystallinity is smaller than that of the case containing In, but the smaller the doping amount, the lower the crystallinity. Since it tends to be good, the second light guide layer having good crystallinity can be obtained by preferably setting the range to 1 × 10 ¹⁸ / cm ³ or less.
In the embodiments described later, the second light guide layer is grown undoped and doped with p-type impurities by diffusion from an adjacent layer. However, the present invention is not particularly limited to this method, and the same applies to other layers. However, either diffusion after growth or a method of growing while doping may be used.

[0032] The second light guide layer may be formed of a single film or a multilayer film. As a multilayer film,
A multilayer film in which a plurality of AlGaN / GaN layers are stacked may be used.
It may be a layer having a composition gradient such that the l-mixed crystal ratio increases as the distance from the light-emitting layer increases.

The second light guide layer may be formed by combining nitride semiconductor layers having different compositions.
This is preferable because light loss due to light can be avoided. At this time, the thickness of the second light guide layer is not particularly limited, but it is preferable that the second light guide layer be formed to have a thickness of at least 200 ° or more.
As a good waveguide, light guiding with low loss is realized, leading to a decrease in the threshold current. At this time, by setting the upper limit of the film thickness to 4000 ° or less, it is possible to suppress an increase in the threshold current and Vf. , Preferably 500 ° or more and 200
By setting the angle to 0 ° or less, the threshold current and Vf can be reduced, and a waveguide having a thickness suitable for guiding light can be formed. This film thickness can also be applied to the n-type layer side of the region between the cladding layer and the light emitting layer, that is, the film thickness of the region between the n-type cladding layer and the light emitting layer. As described above, the thickness of the region sandwiched between the cladding layer and the light emitting layer is substantially the same on both the p-type layer side and the n-type layer side, and a waveguide structure having a symmetrical thickness through the light emitting layer can be obtained. It is preferable that the thicknesses of the two layers are different from each other so that the waveguide structure has an asymmetric thickness, and may be appropriately selected in consideration of the characteristics of the obtained nitride semiconductor device. (P-side electron confinement layer) In the present invention, as a p-type nitride semiconductor layer, particularly in a laser device and an edge emitting device,
It is preferable to provide a p-side electron confinement layer. As this p-side electron confinement layer, a nitride semiconductor containing Al is used. Specifically, Al _γ Ga _{1- γ} N (0 <γ <
Use 1). At this time, the Al mixed crystal ratio γ needs to have a band gap energy (offset) sufficiently larger than that of the light emitting layer so as to function as an electron confinement layer, and at least 0.1 ≦ γ <1. Range, preferably within the range of 0.2 ≦ a <0.5. If γ is 0.1 or less, the laser element does not function as a sufficient electron confinement layer, and if γ is 0.2 or more, sufficient electron confinement (carrier confinement) is performed and carrier overflow occurs. ,
In addition, when it is 0.5 or less, it is possible to grow while suppressing the occurrence of cracks. More preferably, when γ is 0.35 or less, it is possible to grow with good crystallinity. At this time, A
The mixed crystal ratio is preferably larger than that of the p-type cladding layer, because the confinement of carriers requires a nitride semiconductor having a higher mixed crystal ratio than the cladding layer that confines light. . This p-side electron confinement layer can be used in the nitride semiconductor device of the present invention. In particular, when driving with a large current and injecting a large amount of carriers into the light-emitting layer, as in a laser device, the p-side Enables effective carrier confinement compared to the case without an electron confinement layer,
It can be used not only for laser devices but also for high-power LEDs.

The thickness of the p-side electron confinement layer of the present invention is at least 1000 ° or less, preferably 400 ° or less. This is because the nitride semiconductor containing Al has a higher bulk resistance than other nitride semiconductors (not containing Al), and the Al mixed crystal ratio of the p-side electron confinement layer is set higher as described above. Therefore, if it is provided in the element exceeding 1000 °, it becomes an extremely high resistance layer, which causes a large increase in the forward voltage Vf. If it is 400 ° or less, the rise of Vf is suppressed to a low level. It is possible to further suppress the temperature by setting the angle to 200 ° or less. Here, when the lower limit of the film thickness of the p-side electron confinement layer is at least 10 ° or more, preferably 50 ° or more, it functions well as electron confinement.

In the laser device, the p-side electron confinement layer is provided between the light emitting layer and the cladding layer in order to function as an electron confinement layer. Between the layers. At this time, when the distance between the light-emitting layer and the p-side electron confinement layer is at least 1000 ° or less, it functions as carrier confinement, and preferably at 500 ° or less, good carrier confinement becomes possible. . That is, the closer the p-side electron confinement layer is to the light emitting layer, the more effective the function of confinement of the carrier functions. In this case, it is most preferable that a p-side electron confinement layer can be usually provided in contact with the light-emitting layer because no other layer is required. At this time, when the layer located closest to the p-type nitride semiconductor layer in the light emitting layer of the quantum well structure and the p-side electron confinement layer are provided in contact with each other, the crystallinity is deteriorated. It is also possible to provide a buffer layer in crystal growth between them.
For example, the most p-side layer of the light emitting layer is InGaN, AlGa
Providing a buffer layer made of GaN between the N-side p-side electron confinement layer and the lower A-layer than the p-side electron confinement layer.
a buffer layer made of a nitride semiconductor containing Al having a mixed crystal ratio of 1;

Here, as the p-side electron confinement layer, specifically, the closer the p-side electron confinement layer is to the light emitting layer, the lower the threshold current density is, but the closer the p-side electron confinement layer is, the shorter the element life is. Becomes As described above, since the p-side electron confinement layer is a layer having an extremely high resistance as compared with the other layers, a large amount of heat is generated when the element is driven, that is, a high temperature is exhibited in the element. It is considered that this has an adverse effect on the light-emitting layer and the well layer which are weak to heat and greatly reduces the element life.
On the other hand, as described above, the p-side electron confinement layer responsible for confinement of carriers becomes more effective in confining carriers as it approaches the light emitting layer, especially the well layer. Weakens.

Accordingly, the distance between the well layer closest to the p-side electron confinement layer and the p-side electron confinement layer in the light-emitting layer should be at least 10
0 ° or more, preferably 120 ° or more, more preferably 1 ° or more
When the angle is 40 ° or more, a decrease in the life of the element can be suppressed, which is preferable. The distance between the well layer and the p-side electron confinement layer is 10
When the length is shorter than 0 °, the element life tends to be sharply reduced. When the angle is 120 ° or more, the life of the element can be significantly improved. When the angle is 150 ° or more, the life of the element tends to be further improved. However, the tendency of the threshold current density to gradually increase begins to be observed. Furthermore, if the distance is 200
When it is larger than Å, the threshold current density tends to clearly increase, and when it is larger than 400 °, the threshold current density tends to sharply increase. Therefore, the upper limit of the distance is 400 ° or less, preferably, 200 ° or less. This is because the p-side electron confinement layer moves away from the well layer, which lowers the efficiency of carrier confinement. This is mainly attributable to an increase in threshold current density and a decrease in luminous efficiency. it is conceivable that.

The p-side electron confinement layer of the present invention usually has a p-type
Doped with impurities, such as laser devices and high power LEDs
When driving with which large current, the carrier mobility
Doping is performed at a high concentration in order to increase the concentration. Specific doping amount and
At least 5 × 10 ¹⁶/cm^ThreeDope
And preferably 1 × 10¹⁸/cm^ThreeDoping
In the element driven by the large current, 1 × 10¹⁸
/cm^ThreeAbove, preferably 1 × 10¹⁹/cm^ThreeDope more
That is. The upper limit of the amount of the p-type impurity is not particularly limited.
But 1 × 10^{twenty one}/cm^ThreeIt is as follows. Where p
Increased bulk impurity tends to increase bulk resistance
And as a result, Vf rises.
Preferably avoids the required carrier mobility
The minimum p-type impurity concentration that can ensure
You. (P-side ohmic electrode) The nitride semiconductor device of the present invention
And the p-side ohmic electrode is the uppermost surface of the p-type layer
Almost all over the contact layer with a film thickness of 5000 mm or more
Is formed. The substantially entire surface is a p-type contact layer
80% or more of the
It can be uniformly supplied to the semiconductor layer. Also, the p-side
The thickness of the electrode is preferably 5000 to 20000 mm.
More preferably, 5000 to 10000
You. Thus, a p-side ohmic electrode is formed with a thick film.
High reliability can be maintained even when a large current is dropped.
Wear. Further, in the present invention, the light emitting surface is located on the side opposite to the electrode forming surface.
So that the p-side ohmic electrode is formed as a thick film.
By suppressing light leakage from the electrode forming surface.
This is preferable.

Further, the p-side ohmic electrode is preferably a multilayer film having a metal oxide layer, so that a good ohmic property can be obtained even when the p-side ohmic electrode is formed in a thick film. For example, a first metal thin film made of nickel, a second metal thin film made of gold, followed by a metal having a first ionization potential or / and electronegativity larger than nickel,
For example, after forming a p-side ohmic electrode in which oxide thin films such as Cu, Ag, Pd, Pt, and Rh are sequentially stacked on almost the entire surface of the p-type contact layer, an annealing process is performed to form a thick film. Nevertheless, good ohmic contact is obtained, and a nitride semiconductor light emitting device having good external quantum efficiency in a large current region is obtained. Further, in order to improve the bonding property of the p-side ohmic electrode, a similar effect can be obtained by performing an annealing process after providing an Au layer as a pad electrode on the uppermost layer of the electrode.
Further, in order to prevent surface oxidation of the Au layer, SiO _{2 is used.}
It is more preferable to perform annealing after forming the film because the mountability and reliability are improved.

[0040]

[Embodiment 1] Hereinafter, the nitride semiconductor laser device of Embodiment 1 will be described in detail. (Substrate) Here, in this embodiment, a sapphire substrate different from the nitride semiconductor is used as the substrate, but a GaN substrate may be used. Specifically, after growing GaN, which is a nitride semiconductor grown on a heterogeneous substrate, in a thick film and then removing the heterogeneous substrate, a nitride semiconductor substrate made of GaN is obtained.

As a heterogeneous substrate, for example, C-plane, R-plane,
Sapphire, spinel (an insulating substrate such as MgAl ₂ O ₄ , SiC (6H,
H, 3C), ZnS, ZnO, GaAs, Si,
It is possible to grow a nitride semiconductor such as an oxide substrate lattice-matched with the nitride semiconductor, and a substrate material different from the nitride semiconductor can be used. Preferred heterosubstrates include sapphire and spinel. In addition, the heterogeneous substrate may be off-angle, and in this case, it is preferable to use a substrate that is off-angled in a step-like manner because the growth of the underlying layer made of gallium nitride can be performed with good crystallinity. Further, when a heterogeneous substrate is used, a nitride semiconductor serving as a base layer before forming an element structure is grown on the heterogeneous substrate, and then the heterogeneous substrate is removed by a method such as polishing to form a single substrate of the nitride semiconductor. Alternatively, a method of removing the heterogeneous substrate after forming the element structure may be used.

When a heterogeneous substrate is used, the buffer layer
(Low temperature growth layer), nitride semiconductor (preferably GaN)
Forming an element structure through an underlayer made of
The growth of the semiconductor is improved. Also on a heterogeneous substrate
In addition, ELOG (E)
Pitaxially Laterally Overgrowth)
When a conductor is used, a growth substrate having good crystallinity can be obtained. EL
Specific examples of the OG layer include a nitride semiconductor layer on a heterogeneous substrate.
Grown on the surface, making it difficult to grow nitride semiconductors on the surface.
A mask region formed by providing a protective film, etc.
Non-mask areas for growing conductors are set up in stripes.
The nitride semiconductor from the unmasked region.
As a result, in addition to growth in the film thickness direction, growth in the lateral direction is achieved.
Nitride semiconductor also grows in the mask region
And the like. In other forms, heterogeneous
An opening is provided in the nitride semiconductor layer grown on the substrate, and the opening is provided.
The lateral growth from the end face of the opening
Layer. (Buffer layer) On the sapphire substrate, a temperature of 105
0 ° C, TMG (trimethylgallium), TMA
(Trimethylaluminum), ammonia and Al
_0.05Ga _0.95A buffer layer 102 made of N is a 4 μm film
Grow in thickness. This layer is made of an AlGaN n-type contact.
Between the gate layer and the nitride semiconductor substrate made of GaN.
It functions as a buffer layer. Next, it consists of nitride semiconductor
On the underlayer, each layer that forms the element structure is laminated. (N-type contact layer) Next, TM was placed on the obtained buffer layer.
G, TMA, ammonia, silane gas as impurity gas
And Al doped with Si at 1050 ° C._0.05Ga_0.95
An n-type contact layer made of N is grown to a thickness of 4 μm.
You. Underlayer such as n-type contact layer or buffer layer
In the layer, a nitride semiconductor containing Al, specifically, Al_xGa
_1-xBy using N (0 <x ≦ 1), GaN or the like
Compared to nitride semiconductors that do not contain Al, using ELOG
To reduce crystallinity, especially pits
Therefore, there is a tendency that a good underlayer surface can be provided.
It is preferable to use a nitride semiconductor containing the same. (Crack prevention layer) Next, TMG, TMI (trimethyl
Ruindium), using ammonia to raise the temperature to 800 ° C
And In_0.06Ga_0.94N crack prevention layer (shown)
(Not shown) is grown to a thickness of 0.15 μm. What
Note that this crack prevention layer can be omitted. (N-type cladding layer) Next, the temperature was raised to 1050 ° C.
Using TMA, TMG and ammonia as feed gas
Al_0.05Ga_0.95A layer made of N is 25 膜厚 thick
And then stop TMA and use it as impurity gas
5 × 10 Si using silane gas ¹⁸/ Cm³Dope
A B layer made of GaN is grown to a thickness of 25 °.
Then, this operation is repeated 200 times for each layer A and
It is a multilayer film (superlattice structure) having a total thickness of 1 μm by laminating B layers.
A further n-type cladding layer is grown. At this time, Ando
The Al mixed crystal ratio of AlGaN is 0.05 or more and 0.1.
If it is in the range of 3 or less, it can sufficiently function as a cladding layer.
Can be provided. (First Light Guide Layer) Next, at the same temperature,
Using TMG and ammonia, undoped GaN layer
It is grown to a thickness of 0.1 μm. Also, doping the n-type impurity
May be Next, raise the temperature to 800 ° C.
Using TMI (trimethyl indium) and TMG for gas
No, Si-doped In_0.05Ga_0.95N layer with a thickness of 500Å
To form a first optical guide layer. (Light Emitting Layer) Next, the temperature was set to 800 ° C.
I (trimethylindium), TMG
In of the_0.05Ga_0.95N barrier layer, and
Doped In_0.32Ga_0.68A well layer made of N
Layer 2a / well layer 1a / barrier layer 2b / well layer 1b / barrier layer
The layers are laminated in the order of 2c. At this time, as shown in FIG.
The layers 2a, 2b and 2c are formed to a thickness of 130 ° and the well layers 1a,
1b is formed with a thickness of 25 °. The light emitting layer 107 is a total film
A multiple quantum well structure (MQW) having a thickness of about 440 ° is obtained. (P-side electron confinement layer) Next, at the same temperature,
Using TMA, TMG, and ammonia as impurity gas
Cp₂Mg (cyclopentadienyl magnesium)
Using 1 × 10 Mg¹⁹/ Cm³Doped Al_0.3
Ga_0.7N-type p-type electron confinement layer with a thickness of 100 °
Let it grow. This layer does not have to be particularly provided
However, by providing it, it functions as electron confinement and lowers the threshold
It will contribute to. (Second Light Guide Layer) Next, the temperature is set to 1050 ° C.
Using TMG and ammonia as source gas, undoped
The second optical guide layer made of GaN has a thickness of 0.15 μm.
Grow with. The second light guide layer is undoped.
Growth, but p-side electron confinement layer, p-type cladding layer
Mg concentration from 5 × 1 due to diffusion of Mg from adjacent layers
0¹⁶/ Cm³And shows the p-type. When this layer grows
May be intentionally doped with Mg. (P-type cladding layer) Subsequently, at 1050 ° C., undoped A
l_0.05Ga_0.95N layer is grown to a thickness of 25 °
And then stop TMA, Cp_TwoUsing Mg, Mg
A layer made of GaN with a thickness of 25 °
Is repeated 90 times to obtain a superlattice layer having a total film thickness of 0.45 μm.
A p-type cladding layer is grown. Fewer p-type cladding layers
At least one includes a nitride semiconductor layer containing Al,
Nitride semiconductor layers with different band gap energies
When fabricated with a stacked superlattice, one of the impurities
Doping a large number of layers to perform so-called modulation doping
Crystallinity tends to be better, but dope is the same for both
You may. The cladding layer 110 is made of a nitride semiconductor containing Al.
Conductive layer, preferably Al_XGa_1-XN (0 <X ≦ 1)
It is desirable to have a superlattice structure, more preferably
It has a super lattice structure in which GaN and AlGaN are stacked. p
By making the side cladding layer 110 a super lattice structure,
It is possible to increase the Al mixed crystal ratio of the entire cladding layer
The refractive index of the cladding layer itself becomes smaller,
The threshold is lowered because the gap energy increases.
It is very effective in making In addition, the superlattice
The pits generated in the cladding layer itself become superlattice
Less short-circuit occurrences
Become. (P-type contact layer) Finally, at 1050 ° C., the p-type
1 × 10 Mg on the pad layer 110²⁰/cm ^ThreeDope
P-type contact layer 111 made of p-type GaN
It grows with the film thickness of Å. p-type contact layer 111 is p-type
In_XAl_YGa_1-XYN (0 ≦ X, 0 ≦ Y, X + Y ≦ 1)
, Preferably Mg doped G
If it is aN, the most preferable ohmic is the p electrode 120.
Contact is obtained. The contact layer 111 forms an electrode
1 × 10¹⁷/cm^ThreeHigh carrier concentration above
It is desirable that 1 × 10¹⁷/cm^ThreeLower than
Getting a good ohmic with the electrodes tends to be difficult
is there. Further, if the composition of the contact layer is GaN,
It becomes easy to obtain a pole material and a preferable ohmic. reaction
After completion, the wafer is placed in a nitrogen atmosphere in a reaction vessel.
Anneal at 700 ° C to further reduce resistance of p-type layer
I do.

After the nitride semiconductor is grown and the respective layers are stacked as described above, the wafer is taken out of the reaction vessel, and a circular protective film made of SiO ₂ is formed at the center of the surface of the uppermost p-type contact layer. RIE (reactive ion etching) using SiCl ₄ gas to etch n
The surface of the n-type contact layer on which an electrode is to be formed is exposed. The end face of the light emitting layer thus obtained is inclined by 80 degrees with respect to the semiconductor lamination plane.

Next, the wafer is immersed in hydrofluoric acid, and the protective film is removed by a lift-off method. Thus, the protective film provided on the p-type contact layer is removed, and the circular p-type contact layer is exposed.

On the surface of the circular p-type contact layer,
After forming a p-side ohmic electrode made of Ni / Au / RhO ₂ and having a total thickness of 5000 °, annealing is performed.
Also, the surface of the n-type contact layer already exposed has Ti
An n-side ohmic electrode made of / Al is formed so as to surround the p-side ohmic electrode. Thus, the distance between the p-side ohmic electrode and the n-side ohmic electrode can be made constant at any point, and a large current can be uniformly applied to the light emitting layer.

Next, an insulating film made of SiO ₂ is formed by masking a desired region for providing a bonding surface on the p and n electrodes on a surface exposed by etching to form an n electrode.

When the laser device obtained as described above is mounted on a flip chip as an illumination light source, the wavelength 41
At a current drop value of 200 mA, light having an output value of about 100 mW is uniformly emitted from the substrate side.

(Embodiment 2) Following the p-side contact layer, A
Except for performing an annealing treatment after forming the u layer, a nitride semiconductor is formed in the same manner as in the first embodiment, and the same effect as in the first embodiment is obtained by using a flip-chip mounting as a light source for illumination. Further, a light emitting device having higher reliability than that of the first embodiment can be obtained. (Embodiment 3) Following the Au layer, SiO _{2 was} interposed through the Ni layer.
A nitride semiconductor was formed in the same manner as in Example 2 except that annealing was performed after the film was formed, and at least a portion of the SiO ₂ film was removed by wet etching of BHF, and then flip-chip mounted for illumination. When the light source is used, the same effect as that of the second embodiment can be obtained, and a light emitting device with higher reliability than that of the second embodiment can be obtained. (Example 4) In Example 1, a desired region for providing a bonding surface is masked on the p and n electrodes on the surface exposed by etching to form an electrode, and SiO ₂ /
When a nitride semiconductor is formed in the same manner as in Example 1 except that an insulating film and a reflective film made of TiO ₂ are formed, and flip-chip mounting is performed to obtain a light source for illumination, a current drop value of 200 m
In A, light having an output value 20% higher than that of Example 1 is uniformly emitted. (Example 5) In Example 2, a nitride semiconductor was formed in the same manner as in Example 2 except that an insulating film and a reflection film made of SiO ₂ / TiO ₂ were formed, and then a reflection film made of Al was formed. When a light source for lighting is mounted by flip chip mounting,
At a current drop value of 150 mA, light having an output value 50% higher than that of the first embodiment is uniformly emitted.

[0049]

According to the nitride semiconductor device of the present invention, a surface emitting light emitting device for an illumination light source having high external quantum efficiency and excellent device characteristics in a large current region can be obtained. In particular, since the resonance surface, which is the end surface of the light emitting layer, is inclined at an angle of more than 45 degrees and less than 90 degrees with respect to the semiconductor layer lamination surface, light is uniformly emitted in the front direction while maintaining stimulated emission. Can be taken out.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating one embodiment of the present invention.

FIG. 2 is a schematic sectional view illustrating another embodiment of the present invention.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Buffer layer 3 ... n-type contact layer 4 ... n-side cladding layer 5 ... 1st light guide layer 6 ... light emitting layer 7 ... p-side electron Confinement layer 8: second optical guide layer 9: p-type cladding layer 10: p-type contact layer 11: p-side ohmic electrode 12: n-side ohmic electrode 13 ... Insulating film 14 ... Reflective film

Claims (4)

[Claims] 1. A nitride semiconductor light emitting device comprising at least a gallium nitride-based compound semiconductor layer having a structure in which a light emitting layer is sandwiched between a p-type cladding layer and an n-type cladding layer having a smaller refractive index than the light emitting layer. Wherein the end face of the light emitting layer is 4
A nitride semiconductor light emitting device characterized by being inclined at an angle of more than 5 degrees and less than 90 degrees. 2. A p-type contact layer on the p-type cladding layer, and a p-side ohmic electrode having a thickness of 5,000 ° or more is provided on almost the entire surface of the p-type contact layer. 2. The nitride semiconductor light emitting device according to 1. 3. The nitride semiconductor light emitting device according to claim 2, wherein the p-side ohmic electrode is a multilayer film having a metal oxide layer. 4. The nitride semiconductor light emitting device according to claim 1, further comprising a reflection film in contact with an end face of said light emitting layer.