JP2003008059A - Nitride semiconductor light emitting device - Google Patents

Abstract

[57] An object of the present invention is to obtain a sufficient carrier concentration in a p-type semiconductor film even when a p-type semiconductor film is grown on an active layer at a lower growth temperature, and to have high luminance light emission characteristics. Al _x Ga _y In _z N (x + y + z = 1) made p-type conductivity by doping Mg.
In ratio z in the carrier block layer 5 made of
0.015 or more, Ga ratio y is 0.50 or more,
The relationship x / z between the Al ratio x and the In ratio z is 0.8.
Since the ratio is 4 / 0.16 or higher, a high hole concentration can be obtained even when the carrier block layer is grown under low temperature conditions, and thermal damage to the active layer 4 due to high temperature conditions can be prevented. Therefore, a semiconductor light emitting element with high luminous efficiency can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device having at least one p-type semiconductor film grown on an active layer.

[0002]

2. Description of the Related Art Conventionally, it has been well known to use nitride compounds such as GaN, InN and AlN, and mixed crystals thereof as a nitride semiconductor material, for example, In _x Ga.
A nitride-based semiconductor light emitting device in which a _1-x N crystal is used as an active layer and a P-type semiconductor film is grown on this active layer has been manufactured.

[0003]

When a light emitting device is manufactured using a nitride compound and its mixed crystal, the temperature for growing the p-type semiconductor film is higher than that for growing the active layer. Therefore, in the step of growing the p-type semiconductor film on the active layer, thermal strain occurs in the active layer, dislocations, etc. occur, and the luminous efficiency of the active layer decreases. .

On the other hand, in order to solve this problem, when the temperature for growing the P-type semiconductor film is lowered, the grown p-type semiconductor film does not have a sufficient carrier concentration, so that electrons are blocked. The required hetero barrier cannot be obtained. Therefore, there is a problem that it is not easy to manufacture a high-luminance light emitting element.

The present invention has been made in view of the above problems. Even if the growth temperature is lowered and the p-type semiconductor film is grown on the active layer, a sufficient carrier concentration can be obtained in the p-type semiconductor film. An object of the present invention is to provide a semiconductor light emitting device having a high brightness light emitting characteristic.

[0006]

In order to solve the above problems, the nitride semiconductor light emitting device of the present invention has a structure in which Al _x Ga is p-type conductive by doping Mg on the active layer. A nitride-based semiconductor light-emitting device in which a carrier block layer made of _y In _z N (x + y + z = 1) is laminated, wherein the In ratio z of the carrier block layer is 0.015 or more and the Ga ratio y is: 0.50 or more, the relationship x / z between the Al ratio x and the In ratio z is
It is characterized in that it is 0.84 / 0.16 or more.

In the present invention, the p-type conductive clad layer laminated on the carrier block layer contains an In element and is doped with Mg so that the p-type clad layer is formed. It is preferably electrically conductive.

The method for manufacturing a nitride-based semiconductor light-emitting device according to the present invention is the method for manufacturing a nitride-based semiconductor light-emitting device according to the present invention, wherein the carrier block layer is 750 ° C.
It is characterized in that it grows at a temperature of ˜950 ° C.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A nitride-based semiconductor light-emitting device 1 according to the first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a sectional structure of a nitride-based semiconductor light emitting device 1 according to this embodiment.

This nitride-based semiconductor light emitting device 1 has an HV
Ga produced by PE (Hydride VPE) method
On the N substrate 2, a first cladding layer 3 made of _{n-GaN, In x Ga 1} -x N composed of the active layer 4, p-AlGaI
It has a structure in which a carrier block layer 5 made of nN and a second cladding layer 6 made of p-GaInN are sequentially stacked. Further, an electrode 15 is provided on the lower surface of the GaN substrate 2, and a transparent electrode 16 is provided on the upper surface of the second cladding layer 6, and a bonding electrode 17 is provided on a part of the upper surface of the transparent electrode 16. It is provided.

In the nitride-based semiconductor light emitting device 1 of the first embodiment, a GaN substrate is used as the substrate,
Even if a sapphire substrate is used instead of the GaN substrate, the active layer 4
A similar light emitting device can be obtained without affecting the light emission of.

The wavelength of the band-to-band emission of the active layer 4 can be appropriately selected from the ultraviolet region to the red region by changing the composition ratio x in In _x Ga _1-x N forming the active layer 4. . In the first embodiment, the composition ratio x is set to x = 0.16 in order to obtain a light emitting element in the wavelength range of blue light emission.

The carrier block layer 5 and the second cladding layer 6 are each doped with magnesium to a predetermined concentration to have p-type conductivity. The transparent electrode 16 is formed of a thin metal film having a thickness of 20 nm or less over substantially the entire upper surface side of the second cladding layer 6.

Since the transparent electrode 16 is formed over almost the entire upper surface of the second clad layer 6, a current flows from the bonding electrode 17 toward the second clad layer 6,
That is, when holes are injected, the second clad layer 6 having a high resistance prevents the current density in the active layer 4 from becoming non-uniform, and as a result, the active layer 4 is made to emit light uniformly over the entire surface. be able to.

The metals used to form the transparent electrode 16 are Ta, Co, Rh, Ni, Pd,
It is desirable to contain any one of Pt, Cu, Ag, and Au.

The electrode 15 provided on the GaN substrate 2 is made of metal. As the metal, Al, T
It is desirable to contain any one of i, Zr, Hf, V, and Nb.

Next, a method of manufacturing the nitride-based semiconductor light emitting device of this embodiment will be described.

First, a sapphire substrate having a (0001) plane is washed, and an MOCVD (Metal Organic Chemical Vapor Deposition) method is used to form an undoped G on the sapphire substrate.
The aN film is grown as a base film.

A method of growing this undoped GaN film will be described.

First, the cleaned sapphire substrate is MO
Introduced into a CVD apparatus, and in a hydrogen (H ₂ ) atmosphere, about 11
The cleaning process is performed under a high temperature condition of 00 ° C. Then, the temperature is lowered to 10 L / min. As a carrier gas. While flowing hydrogen gas at a flow rate of
Under the temperature condition of 0 ° C., 5 L / min. Flow rate of NH ₃ and 20 mol / min. Flow velocity of trimethylgallium (T
The GaN low temperature buffer layer is grown to a thickness of about 20 nm by introducing each of MG).

After that, the supply of TMG is once stopped, the temperature is raised again to about 1050 ° C., and then TMG is returned to about 10
0 mol / min. At a flow rate of 1 hour for 1 hour to grow an undoped GaN film having a thickness of about 3 μm.

After that, the supply of TMG and NH ₃ was stopped, the temperature inside the MOCVD apparatus was lowered to room temperature, and undoped G
The sapphire substrate on which the aN underlayer is grown is taken out.

The low temperature buffer layer has the above-mentioned G content.
Not limited to aN film, trimethyl aluminum (TM
An AlN film or a GaAlN film may be formed by using A), TMG, or NH ₃ .

Next, on the sapphire substrate on which the undoped GaN underlayer produced by the above method is grown, Ga
In order to prevent cracks from occurring in the GaN thick film when the N thick film is grown, the thickness is 0.2 μm and the interval is 10 μm.
After forming the m-shaped stripe-shaped growth suppressing film, a flat GaN thick film is grown on this growth suppressing film by selective growth using the H-VPE method. As this growth suppressing film,
A dielectric such as SiO ₂ or SiN _x or a refractory metal such as W can be used. In this embodiment, a SiO ₂ film deposited by sputtering is etched by photolithography.

Next, a GaN thick film is grown on the undoped GaN underlayer on which the growth suppressing film is formed.

First, a sapphire substrate on which an undoped GaN base film having a stripe-shaped growth suppressing film formed by the above-described method is grown is introduced into an H-VPE apparatus, and a nitrogen gas (N ₂₎ which is a carrier gas is introduced. ) And NH ₃ gas at 5 L / min. While flowing at the flow rate of
The temperature inside the VPE apparatus is raised to about 1050 ° C. After that, 100 cc / mi of GaCl was formed on the sapphire substrate.
n. At a flow rate of 1 to start the growth of a GaN thick film.
It should be noted that an impurity doping line for supplying impurities is previously piped in the H-VPE device so as to reach a position close to the substrate, and at the same time when the growth of this GaN thick film is started, the impurity doping line is required from the impurity doping line. By introducing the above impurity gas, it is possible to dope the GaN thick film with impurities at an arbitrary concentration.

In this embodiment, at the same time as the growth of the GaN thick film is started, monosilane (SiH ₄ ) is added to 200 nm.
ol / min. By supplying at a flow rate of, the impurity Si is introduced at a concentration of about 3.8 × 10 ¹⁸ cm ⁻³ ,
A Si-doped GaN film was grown.

A GaN thick film was grown by the above method for 6 hours to grow a GaN thick film having a thickness of about 700 μm. After the growth of the GaN thick film, the sapphire substrate was removed by polishing to obtain a GaN substrate 2.

Next, a light emitting device structure is grown by MOCVD on the GaN substrate 2 obtained by the method described above.

First, the GaN substrate 2 is introduced into the MOCVD apparatus, and nitrogen gas (N ₂ ) and NH ₃ gas are each added to 5 times.
L / min. The temperature inside the MOCVD apparatus is raised to about 1050 ° C. while flowing at a flow rate of When the temperature rise was completed, the carrier gas was replaced with nitrogen gas (N ₂ ) by hydrogen gas (H ₂ ), and TMG was added at 100 μmol / min. Flow velocity, S
iH ₄ at 10 nmol / min. At a flow rate of about 1 μm for the first cladding layer 3 made of n-GaN.
It grows to a thickness of m. After that, stop the supply of TMG,
The carrier gas is returned from hydrogen gas (H ₂ ) to nitrogen gas (N ₂ ) and the temperature of the MOCVD apparatus is lowered to 760 ° C.

Next, the active layer 4 is formed on the first cladding layer 3. First, trimethyl indium (TMI), which is an indium raw material, was added at 6.5 μmol / min. Flow rate of TMG at 2.8 μmol / min. At a flow rate of 3 to form a well layer of In _0.18 Ga _0.72 N with a thickness of 3 nm. Then, the temperature is raised again to 850 ° C.
MG at 14 μmol / min. At a flow rate of
A barrier layer made of N is grown. Thereafter, the growth of the well layer and the barrier layer described above is sequentially repeated, and a total of five well layers and a total of five barrier layers are alternately stacked on the bottom barrier layer to form a multiple quantum well (MQW). ) Active layer 4
To grow.

Next, the carrier block layer 5 is grown on the active layer 4.

First, TMG is formed at the same temperature as when the barrier layer, which is the uppermost layer of the active layer 4 composed of multiple quantum wells, is formed.
Of 11 μmol / min. Flow rate, TMA 1.1 μm
ol / min. Flow rate and TMI of 40 μmol / mi
n. At a flow rate of 10 nmol of biscyclopentadienyl magnesium (hereinafter referred to as Cp ₂ Mg) which is a p-type doping source gas.
/ Min. Flow rate of p-type Al _0.20 Ga _0.75 In
_A carrier block layer 5 made of _0.05 N is grown to a thickness of 50 nm.

After the growth of the carrier block layer 5, the supply of TMA is stopped and the p-type Ga _0.91 In _0.09 N is _added.
The second clad layer 6 consisting of is grown to complete the growth of the light emitting device structure.

Then, after stopping the supply of each of TMG, TMI, and Cp ₂ Mg, the temperature inside the MOCVD apparatus is lowered to room temperature, and the GaN substrate on which the light emitting element structure is formed is MO-deposited.
Take out from the CVD device.

Then, after the thickness of the GaN substrate 2 is adjusted appropriately, a transparent electrode 16 is formed on the upper surface of the second cladding layer 6 made of a p-type Ga _0.91 In _0.09 N layer, and the transparent electrode 16 is formed on the transparent electrode 16. The bonding electrode 17 is formed at a predetermined position. Further, the electrode 15 is formed on the lower surface of the GaN substrate 2, and the manufacture of the nitride-based semiconductor light emitting device of the first embodiment is completed.

The p-type semiconductor films of the carrier block layer 5 and the second cladding layer 6 of the nitride-based semiconductor light-emitting device produced as described above are Mg-type in order to have p-type conductivity.
Is doped. In this case, Al _x Ga _y In _z
If the composition ratio of In in the p-type semiconductor film formed from a mixed crystal of N is increased, the energy of the valence band in the energy band is reduced with the increase, and the energy approaches the acceptor level of Mg. It is known that a high hole concentration can be obtained.

Next, based on the above knowledge, the p-type carrier block layer 5 made of Mg-doped Al _x Ga _y In _z N (x + y + z = 1) was formed on the active layer by lowering the growth temperature. The range of conditions for maintaining a sufficient carrier concentration even when the carrier block layer is grown will be described.

In FIG. 2, p-type Al _x Ga _y In _z N (x
+ Y + z = 1) With respect to the carrier block layer, the optimum condition range obtained as a result of various studies on conditions for having a sufficient carrier concentration is shown by the shaded area in the figure.

That is, p-type Al _x Ga _y In _z N (x
In the carrier block layer 5 composed of + y + z = 1), when the In composition ratio z was lower than 0.015, a sufficient carrier concentration was not obtained in the carrier block layer grown at low temperature. Therefore, in order to obtain a sufficient carrier concentration in the carrier block layer 5, it was found that the composition ratio z of In needs to be 0.015 or more.

When the ratio y of Ga is lower than 0.50 and the ratio x of Al is relatively high,
As a result of making it difficult for each element to mix uniformly, the crystallinity deteriorates, and since Mg, which is a dopant, also becomes difficult to mix uniformly, it was not possible to obtain a sufficient carrier concentration in the carrier block layer. Therefore, it was found that the Ga composition ratio needs to be 0.50 or more in order to obtain a sufficient carrier concentration in the carrier block layer 5.

Further, the lattice constant of the carrier block layer 5 is larger than the lattice constant of the active layer 4, and compressive stress is applied in the vicinity of the active layer 4. On the other hand, compressive stress due to the GaN substrate 2 is applied to the active layer 4 using GaInN as a light emitting layer, and therefore the lattice constant of the active layer 4 is distorted. Therefore, in order to bring the lattice constant of the carrier block layer 5 close to the distorted lattice constant of the active layer 4, it is considered that a higher Al ratio is preferable.

A light emitting device having a carrier block layer 5 manufactured with the relation x / z between the ratio x of Al and the ratio z of In being x / z = 0.84 / 0.16 or more is A
Compared to a light emitting device having a carrier block layer 5 in which the relationship between the ratio x of l and the ratio z of In is equal to or less than the above conditions, the time until the emission intensity is reduced by half is about 1.5 times longer, and 1000 It was confirmed that the emission intensity was not halved over a period of time and the life was extended.

Next, in the growth steps of both the carrier block layer 5 and the second cladding layer 6 each doped with Mg, the growth temperature Tg and the growth temperature Tg for the case of introducing the In element and the case of not introducing the In element respectively. The relationship with the driving voltage Vf of the semiconductor light emitting element will be described.

FIG. 3 shows the growth temperature Tg when the In element was introduced and when the In element was not introduced.
6 is a graph showing the relationship between the drive voltage Vf of the semiconductor light emitting device and the drive voltage Vf.

According to FIG. 3, when the In element is not introduced into the carrier block layer 5 and the second cladding layer 6,
When the growth temperature Tg was set to 1000 ° C. or lower, the driving voltage Vf was remarkably increased. This is the produced carrier block layer 5 and the second cladding layer 6
In addition, it is considered that the resistance of these layers increased because a sufficient carrier concentration could not be obtained.

On the other hand, when In is introduced into the carrier block layer 5 and the second cladding layer 6, it is 850
Carrier block layer 5 and second cladding layer 6 at about ℃
It is considered that, even after growing, the driving voltage Vf of the semiconductor light emitting element did not increase, and a sufficient carrier concentration was obtained in the carrier block layer 5 and the second cladding layer 6.

As a result, by introducing In, even if the carrier block layer 5 and the second cladding layer 6 are produced under the above-mentioned low temperature condition, a sufficient carrier concentration can be obtained in each of these layers. I knew I could do it. In this case, since the carrier block layer 5 and the second cladding layer 6 are formed under such a low temperature condition, thermal damage to the active layer 4 due to a high temperature condition is prevented, so that light emission with high luminous efficiency is achieved. An element can be obtained.

(Embodiment 2) In the nitride-based semiconductor light-emitting device 1 of Embodiment 1 described above, as the active layer 4,
Although In _x Ga _1-x N is used, in the nitride-based semiconductor light-emitting device 1 of the present Second Embodiment, 100 cc of AsH ₃ (arsine) is simultaneously introduced in the step of forming the active layer 4. In _0.05 Ga _0.95
The active layer 4 made of AsN was produced. Other configurations are similar to those of the nitride-based semiconductor light emitting device 1 of the first embodiment, and detailed description thereof will be omitted.

In the second embodiment, a red light emitting device having a light emission output and life characteristics similar to those of the nitride-based semiconductor light emitting device 1 of the first embodiment and having a peak wavelength at 630 nm was obtained. In this light emitting element, it is estimated that As is mixed in about 1 to 5%.

(Third Embodiment) In the nitride-based semiconductor light-emitting device 1 of the first embodiment described above, the active layer 4 is
Although In _x Ga _1-x N is used, in the nitride-based semiconductor light-emitting device 1 of the third embodiment, 500 cc of PH ₃ (phosphine) is simultaneously introduced in the step of forming the active layer 4. In _0.05 Ga _0.95
The active layer 4 made of PN was produced. Other configurations are similar to those of the nitride-based semiconductor light emitting device 1 of the first embodiment, and detailed description thereof will be omitted.

In the third embodiment, a red light emitting device having a light emission output and life characteristics similar to those of the nitride-based semiconductor light emitting device 1 of the first embodiment and having a peak wavelength at 610 nm was obtained. In this light emitting element, it is estimated that P is mixed in about 1 to 5%.

[0054]

As described above, the nitride-based semiconductor light emitting device of the present invention is doped with Mg to improve the p-type conductivity.
_-Type conductivity type Al _x Ga _y In _z N (x + y + z =
Ratio z of In in the carrier block layer consisting of 1)
Is 0.015 or more, the Ga ratio y is 0.50 or more,
The relationship x / z between the ratio x of Al and the ratio z of In is 0.8
Since it is set to 4 / 0.16 or more, a high hole concentration can be obtained even if the carrier block layer is grown under low temperature conditions, and thermal damage to the active layer due to high temperature conditions can be prevented. Therefore, a semiconductor light emitting device having high luminous efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a light emitting device of an embodiment of the present invention.

FIG. 2 is a diagram showing a condition range suitable for obtaining a high hole concentration in a carrier block layer made of Al _x Ga _y In _z N (x + y + z = 1).

FIG. 3 is a graph showing the relationship between the growth temperature and the drive voltage of In with and without addition of In in the Mg-doped carrier block layer and the second cladding layer.

[Explanation of symbols]

1 Nitride semiconductor light emitting device 2 GaN substrate 3 First clad layer 4 Active layer 5 Carrier block layer 6 Second clad layer 15 electrodes 16 Transparent electrode 17 Bonding electrode

Claims (3)

[Claims] 1. An Al _x Ga _y In _z N (x which is made p-type conductive by doping Mg on the active layer.
+ Y + z = 1) is a nitride-based semiconductor light-emitting device in which a carrier block layer of (1) + y + z = 1) is laminated, and the In ratio z in the carrier block layer is 0.
015 or more, the ratio y of Ga is 0.50 or more, and the relationship x / z between the ratio x of Al and the ratio z of In is 0.84 / 0.
A nitride-based semiconductor light-emitting device characterized by having 16 or more. 2. The p-type conductive clad layer laminated on the carrier block layer contains an In element and is doped with Mg to obtain p-type conductivity. The nitride-based semiconductor light emitting device according to claim 1, wherein 3. The method for manufacturing a nitride-based semiconductor light-emitting device according to claim 1, wherein the carrier block layer is grown at a temperature of 750 ° C. to 950 ° C. Method for manufacturing light emitting device.