JP2002280611A - Semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element having a new structure for leading the lateral light generated in a light-emitting layer toward the outside. SOLUTION: A first layer 1 is processed so that an uneven surface 1a is formed on the surface thereof, a second layer 2 having a refractive index different from that of the first layer is grown so as to fill the uneven surface (alternatively, a first crystal 10 is grown to be uneven on a crystal layer S as a base of growing, and a second crystal 20 having a refractive index different from that of the first crystal is grown). After forming the uneven refractive-index interface 1a (10a), an element structure is formed on which a semiconductor crystal layer including a light-emitting layer A is laminated thereon. Thus, the lateral light generated in the light-emitting layer is affected by the interface having an uneven refractive index, and changes its direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light-emitting device (hereinafter, also simply referred to as "light-emitting device"), and more particularly to a device whose light-emitting layer is made of a GaN-based semiconductor crystal (GaN-based crystal).

[0002]

2. Description of the Related Art The basic element structure of a light emitting diode (LED) is such that an n-type semiconductor layer and a light emitting layer (DH) are formed on a crystal substrate.
Structure, MQW structure, and SQW structure) and a p-type semiconductor layer are sequentially grown, and an external extraction electrode is formed on each of the n-type layer and the p-type layer.

[0003] For example, FIG. 8 is a diagram showing an example of a configuration of a device (GaN-based LED) using a GaN-based semiconductor as a material of a light-emitting layer.
Type GaN contact layer (also a cladding layer) 102,
A GaN-based semiconductor light emitting layer 103 and a p-type GaN contact layer (also a clad layer) 104 are sequentially stacked by crystal growth, and a lower electrode (usually an n-type electrode) 1
05, an upper electrode (usually a p-type electrode) 106 is provided. Here, the description will be made on the assumption that the mounting is performed with the crystal substrate facing down, and light is emitted upward.

In an LED, how efficiently light generated in the light emitting layer can be extracted to the outside world (so-called light extraction efficiency) is an important issue. For this reason, in the related art, for light traveling upward from the light emitting layer, the upper electrode 106 in FIG. 8 is made to be a transparent electrode so as not to be an obstacle to the outside. Various measures have been taken, such as a mode in which a reflective layer is provided and turned upward.

[0005]

With respect to the light emitted from the light emitting layer in the vertical direction, it is possible to improve the efficiency of extracting light to the outside by providing the electrodes with a transparent layer or a reflective layer as described above. Although it is possible, it is defined by the refractive index difference among the light generated in the direction in which the light emitting layer spreads (the direction indicated by a thick arrow in the light emitting layer 103 in FIG. 8, hereinafter also referred to as “lateral direction”). Light reaching the side wall within the total reflection angle can be radiated to the outside, but many other lights are only absorbed and attenuated and disappear in the element by, for example, repeating reflection on the side wall. Such lateral light is confined by upper and lower cladding layers or a substrate (sapphire substrate) and an upper cladding layer, or a substrate and an upper electrode (further, a coating material outside the element, etc.) and propagates in the lateral direction. It is. The light propagating in the lateral direction occupies most of the total amount of light generated in the light emitting layer, and may reach 60% of the whole.

Further, in a flip-chip type LED (light is emitted to the outside through the substrate) mounted with the substrate on the upper side, the element structure is designed to reflect such lateral light in the direction of the substrate. It is known that an angle is formed on the side wall of the laminate and the side wall is used as a reflection surface toward the substrate. However, it is difficult to perform processing such as cutting the four surfaces of a fine chip at an angle, and this poses a problem in terms of cost.

An object of the present invention is to solve the above-mentioned problems and to provide a light-emitting element provided with a novel structure for directing lateral light generated in a light-emitting layer to the outside.

[0008]

SUMMARY OF THE INVENTION The present invention has the following features. (1) Asperities are processed on the surface of the first crystal layer, and
A second crystal layer made of a semiconductor material having a refractive index different from that of the crystal layer is grown via the buffer layer or directly by embedding the irregularities, and a semiconductor including a light-emitting layer thereon. A semiconductor light emitting device having an element structure in which crystal layers are stacked. Hereinafter, this mode (1) will be described as "mode (I)".

(2) The semiconductor light emitting device according to the above (1), wherein the second crystal layer and the semiconductor crystal layer thereover are layers composed of a GaN-based semiconductor crystal.

(3) The first crystal layer is a crystal substrate, and the second crystal layer is grown while forming a substantially facet structure from an uneven surface processed on the surface of the crystal substrate. The semiconductor light emitting device according to (2).

(4) The unevenness processed on the surface of the crystal substrate is an unevenness exhibiting a stripe pattern, and the longitudinal direction of the stripe is the GaN grown by embedding it.
<11-20> direction of system semiconductor or <1-100>
The semiconductor light emitting device according to the above (2) or (3), which is a direction.

(5) The semiconductor light-emitting device according to any one of (1) to (4), wherein the cross-sectional shape of the unevenness is rectangular, triangular, or sine curve.

(6) The difference between the refractive index of the first crystal layer and the refractive index of the second crystal layer at the wavelength of light emitted from the light emitting layer is 0.05 or more. The semiconductor light emitting device according to any one of (5) and (5).

(7) A first GaN-based semiconductor crystal is grown on the surface of a crystal layer serving as a basis for crystal growth so as to form irregularities.
Second Ga having a different refractive index from the aN-based semiconductor crystal
An N-based semiconductor crystal is growing, and a third GaN
A semiconductor light emitting device having an element structure in which a system semiconductor crystal is grown until the irregularities are flattened, and a semiconductor crystal layer including a light emitting layer is stacked thereon. Hereinafter, the mode (7) will be described as "mode (II)".

(8) A structure or surface treatment for dimensionally limiting the crystal growth region is applied to the surface of the crystal layer, which is the basis for crystal growth, whereby the first GaN-based semiconductor crystal is substantially reduced. The semiconductor light emitting device according to the above (7), wherein the semiconductor light emitting device is grown so as to form irregularities while forming a facet structure or a pseudo facet structure.

(9) A structure or surface treatment for dimensionally limiting the crystal growth region is provided on the surface of the crystal layer serving as the basis for crystal growth or on the surface of the crystal layer serving as the basis for crystal growth. (8) The semiconductor light emitting device according to the above (8), wherein the semiconductor light emitting device is a mask pattern capable of lateral growth or a surface treatment applied to a specific region of a crystal layer surface serving as a basis for crystal growth to suppress GaN-based crystal growth.

(10) The second Ga layer is formed by covering at least the projections among the projections and depressions of the first GaN-based semiconductor crystal in a film shape.
An N-based semiconductor crystal is grown, and a third GaN-based semiconductor crystal is grown to cover the N-based semiconductor crystal until the irregularities are flattened, and a semiconductor crystal layer including a light emitting layer is laminated thereon. Semiconductor light emitting device having an element structure
The semiconductor light emitting device according to any one of the above (7) to (9), wherein the second GaN-based semiconductor crystal has a multilayer structure.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Since the object of the present invention has the most important meaning for a light emitting device, the light emitting device according to the present invention is most preferably an LED. Although the material system is not limited, as described later, an LED (GaN-based LE) using a GaN-based material in which the usefulness of the present invention is particularly remarkable.
The light-emitting element will be described with reference to D) as an example.

In any of the embodiments, the light-emitting element has an uneven refractive index interface provided below the light-emitting layer, and the light-extraction efficiency is improved by its operation and effect. From the viewpoint of how the uneven refractive index interface is formed, the light-emitting element has the following modes (I) and (II).
It can be further divided. In the above embodiment (I), the crystal substrate is processed to have irregularities, and the irregularities are processed into a semiconductor crystal (especially GaN).
(A system crystal) to form an uneven refractive index interface. In the above mode (II), a GaN-based crystal is grown in irregularities, and the GaN-based crystal is buried with another GaN-based crystal to form an uneven refractive index interface.

First, the embodiment (I) will be described. FIG. 1A is a diagram illustrating a GaN-based LED as a structural example of a light-emitting device according to the embodiment (I), in which a GaN-based LED is provided on a surface of a first crystal layer (hereinafter, also referred to as a “first layer”) 1. Unevenness 1a
Is processed, and a second crystal layer (hereinafter, also referred to as “second layer”) 2 made of a material having a different refractive index from the crystal layer is formed thereon via a buffer layer or directly, It grows by embedding the irregularities. As a result, interfaces having different refractive indices are uneven. Further on that,
Semiconductor crystal layers (n-type contact layer 3, light-emitting layer A, p-type contact layer 4) are stacked by crystal growth, and an electrode P
1, P2 is formed to form an element structure. The device structure shown in the figure is a simple DH structure, but a special contact layer, a special cladding layer, etc. are provided, and the light emitting layer is SQ.
It may have a W structure or an MQW structure, and may have a structure as any light emitting element.

According to the above configuration, the light propagating in the lateral direction generated in the light emitting layer A is affected by the uneven refractive index interface 1a, and a kind of mode conversion occurs (the light traveling direction in the surface light emitting direction due to irregular reflection). ), And head in a direction other than the horizontal direction. As a result, the amount of light traveling toward the extraction surface increases, and the light extraction efficiency improves.

As described in the description of the related art, in the related art, light traveling in a direction other than the light outlet (for example, downward or lateral direction) is merely reflected by the end face. Was trying to go to the outlet. On the other hand, in the present invention, a GaN-based semiconductor layer region formed on a substrate by epitaxial growth is regarded as a [waveguide for propagating light in the lateral direction], and light guided in the lateral direction along the waveguide. By forming a concave-convex refractive index interface at a position that can affect light, a kind of mode conversion (or diffuse reflection) is caused to direct light in another direction.

In the present invention, attention is paid to the fact that the light propagating in the lateral direction is propagated in the lateral direction as an electromagnetic wave with the electric field largely spread to the layers above and below the light emitting layer. The thickness of the light emitting layer is 1 in an ordinary active layer having a DH structure.
It is about 0 nm to 100 nm. The light in the lateral direction propagates not only in such a thin active layer but also as a wave having a wide distribution width reaching the crystal substrate. Therefore, as shown in FIG. 1 (a), if the uneven refractive index interface 1a is formed within the range of the light distribution in the horizontal direction, the wave of the light in the horizontal direction is affected, and a kind of mode conversion is performed. Some amount can be redirected in the other direction (or cause diffuse reflection), thus increasing the amount of light that exits to the outside world. The unevenness also functions as a reflection surface for irregularly reflecting light emitted from the light emitting layer toward the unevenness itself.

In the embodiment (I), the irregularities processed on the surface of the first layer are irregularities formed by the surface of the first layer itself. This is because Si used in a conventionally known lateral growth method is used.
The mask layer made of O ₂ or the like is different from the unevenness formed on the flat surface.

The overall arrangement pattern of the irregularities may be any as long as it can affect the wave motion of the light in the horizontal direction, and a dot-like concave part (or convex part) is formed on the surface (reference plane) of the first layer.
May be arranged, or a stripe-shaped uneven pattern in which linear or curved concave grooves (or convex ridges) are arranged at regular intervals. A pattern in which the convex ridges have a lattice shape can be said to be a pattern in which angular concave portions are arranged. Among these, the stripe-shaped uneven pattern can have a strong influence on the light in the horizontal direction.

The cross-sectional shape of the irregularities is rectangular (including trapezoidal) as shown in FIG. 2A, triangular or sine as shown in FIG. 3C. And a wave-like composite. For details of the details of the irregularities, reference may be made to an irregular structure for crystal growth formed for reducing the dislocation of the GaN-based crystal, which will be described later.

In order for the unevenness to affect light in the horizontal direction, the unevenness is preferably within a specific distance from the light emitting layer. This distance is about 0.5 μm to 20 μm, particularly 1 μm to 1 μm, as indicated by k in FIG.
0 μm is a preferable value, and the distance between the upper surface of the substrate and the lower surface of the light emitting layer in a normal LED is included in this range. Therefore, if the crystal structure of the element is used as the first layer to form irregularities on the upper surface, and the second layer is grown so as to bury the element, and the element structure is formed, the irregularities sufficiently affect the lateral light. give.

The material system of the light emitting device is a GaAs system,
Conventionally known materials such as an nP-based material and a GaN-based material may be used, but Ga which has a large problem of lowering the dislocation of the crystal.
The utility of the present invention is most remarkable in an N-based light-emitting element (at least a material of a light-emitting layer is a GaN-based semiconductor). In a GaN-based light-emitting device, it is an essential precondition for forming a GaN-based crystal to reduce dislocations. In the present invention, a growth method using a concavo-convex structure useful for reducing the dislocation of a GaN-based crystal is provided as follows, and the concavo-convex structure can be used also as the concavity and convexity of the refractive index interface. Therefore, the usefulness of the unevenness is higher than when the unevenness is formed only for the purpose of the refractive index interface. Hereinafter, a GaN-based crystal growth method using this uneven structure will be described.

The GaN-based crystal growth method using the uneven structure is as follows.
As shown in FIG. 2A, irregularities 1a are formed on the surface of the crystal substrate (first layer) 1, and as shown in FIG. 2B, GaN-based crystals 21 and 22 are formed from the concave and convex portions. By growing while substantially forming a facet structure,
As shown in FIG. 2 (c), G
This is a method of substantially filling with an aN-based crystal and filling the irregularities to grow. The growth while substantially forming the facet structure means growth including growth similar to the growth of the facet structure described later (for example, growth while forming irregularities in the thickness direction). Hereinafter, the growth method of filling the concave portion using the unevenness is referred to as “the facet growth method”.

In the facet growth method used in the present invention, irregularities are formed on the surface of a crystal substrate in which even a buffer layer or the like is not formed, so that a ground surface on which a facet surface can be formed from the beginning of crystal growth is formed in advance. The feature is that it is provided. By providing irregularities on the crystal substrate, a concave surface and a convex surface defined by a mutual step are used as a unit reference surface on which facet structure growth is generated when a GaN-based crystal is vapor-phase grown on this surface. By making both the concave surface and the convex surface a surface on which the facet structure can be grown, as shown in FIG. 2B, crystal growth that exhibits a convex shape from both the concave surface and the convex surface occurs at the initial stage of growth.

As a result, the dislocation line extending from the crystal substrate in the C-axis direction is shifted to the facet plane (crystals 21 and 2 shown in FIG. 2B).
(2 slopes) and is no longer propagated upward. Thereafter, as shown in FIG. 2C, when the growth is continued and the growth surface is planarized, the vicinity of the surface becomes a low dislocation density region in which the propagation of dislocations from the substrate is reduced.

In a general method of growing a GaN-based crystal, a MOVPE method or the like is used to deposit Al on a sapphire C-plane substrate.
A high-temperature GaN film is grown via a low-temperature buffer layer such as N. When high-temperature GaN is grown on the low-temperature buffer layer, the high-temperature GaN crystal starts island-like growth with some of the crystallized buffer layer as the nucleus for growth, but the crystal with a high growth rate replaces the crystal with a low growth rate. It merges to cover and promotes lateral growth, and eventually a flat GaN crystal is formed. At this time, when the sapphire substrate is not processed with irregularities, the growth proceeds so that a stable C-plane appears with a low growth rate, so that the sapphire substrate is flattened. This is because the growth rate in the lateral direction is higher than the growth rate of the stable C-plane. On the other hand, processing the unevenness on the substrate surface adds a dimensional limit to the crystal growth region to the lateral growth. For example, if the longitudinal direction of the unevenness is a stripe shape parallel to the <11-20> direction, Since the growth in the <1-100> direction is restricted, the growth rate in the C-axis direction is increased, and a stable oblique facet such as {1-101} can be formed at a low crystal growth rate. In the present invention, by performing unevenness processing on the growth surface of the substrate,
The dimensional limitation of the growth region for the lateral growth is added.

The fact that the second layer substantially fills the recesses means not only a completely filled state, but also a filling that forms an effective uneven refractive index interface capable of achieving the object of the present invention. For example, a gap may be formed in a portion where a crystal grown from a concave portion and a crystal grown from a convex portion are united, which is advantageous in that a change in refractive index can be obtained. In addition, even when a gap is formed on the concave portion, the lower surface of the second layer grown on the concave portion,
It suffices if it penetrates into the concave portion to the extent that the object of the present invention can be achieved, and forms an effective uneven refractive index interface.

For the facet growth method, for example,
Japanese Patent Application Laid-Open No. 2000-106455 discloses a method of growing a gallium nitride-based semiconductor so as to provide irregularities on a crystal substrate and leave the concave portions as cavities. However, in such a growth method, since the concave portion is not filled and is left as a hollow portion, the refractive index interface when viewed from the second layer (ie,
The lower surface of the second layer) is not sufficiently uneven, and the mode modulation effect on the light in the lateral direction is small. Moreover,
The existence of the cavity is disadvantageous in dissipating the heat generated in the light emitting layer to the substrate side. In addition, since the propagation of dislocations is not actively controlled, the dislocations propagate above the convex portions, and the effect of reducing the dislocation density is insufficient.

The crystal substrate used in the facet growth method is a substrate serving as a base for growing various semiconductor crystal layers, in which a buffer layer or the like for lattice matching has not been formed yet. To tell. Preferred crystal substrates are sapphire (C-plane, A-plane, R-plane), SiC
(6H, 4H, 3C), GaN, AlN, Si, spinel, ZnO, GaAs, NGO, and the like can be used, but other materials may be used if they correspond to the object of the invention. The plane orientation of the substrate is not particularly limited,
Further, it may be a just substrate or a substrate having an off angle.

The GaN-based semiconductor is In _x Ga _Y Al _Z N
(0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z =
1) The compound semiconductor shown in 1), in which the mixed crystal ratio is arbitrary, for example, AlN, GaN, AlGaN, InG
aN and the like are mentioned as important compounds.

The unevenness used in the facet growth method is, as described above, an uneven shape capable of causing facet structure growth from both the concave surface and the convex surface, and an uneven shape capable of acting on lateral light generated in the light emitting layer. Preferably, it is shaped.
Preferred patterns of the irregularities and preferred specifications of the irregularities will be described below.

The arrangement pattern of the concavities and convexities used in the facet growth method may roughly refer to the concavities and convexities that can affect the wave motion of the light in the lateral direction, and may include dot-like concave portions (or convex portions). , And a striped uneven pattern in which linear or curved concave grooves (or convex ridges) are arranged at regular intervals. In addition, the cross-sectional shape of the unevenness includes a rectangular (including trapezoidal) wavy shape, a triangular wave shape, a sine curve shape, and the like, and the pitch is not necessarily required to be constant as described above. Among these various irregularities, the stripe-shaped irregular pattern in which linear or curved concave grooves (or convex ridges) are arranged at regular intervals can simplify the production process and facilitate the production of the pattern. However, as described above, this is preferable because the influence on the light in the horizontal direction is large.

When the concavo-convex pattern has a stripe shape, the longitudinal direction of the stripe may be arbitrary,
For a GaN-based crystal that grows with this embedded, <11
When the -20> direction is set, oblique facets such as the {1-101} plane are likely to be formed when dimensional restrictions are imposed on the lateral growth. As a result, dislocations that have propagated in the C-axis direction from the substrate side are bent laterally on the facet surface, and are less likely to propagate upward, which is particularly preferable in that a low dislocation density region can be formed.

On the other hand, the longitudinal direction of the stripe is set to <1-10
Even in the case of the <0> direction, the same effect as described above can be obtained by selecting a growth condition in which a pseudo facet surface is easily formed.

As an example, the cross-section as shown in FIG. 2A is a rectangular wave-shaped unevenness, and the facet growth method and preferable dimensions of the unevenness that can effectively affect the direction of light in the lateral direction are as follows. The width W1 of the concave groove is preferably 0.5 μm to 20 μm, particularly preferably 1 μm to 10 μm. The width W2 of the protruding portion is 0.
5 μm to 20 μm, particularly preferably 1 μm to 10 μm.
The amplitude of the unevenness (depth of the groove) d is 0.05 μm to 5 μm.
m, particularly preferably 0.2 μm to 3 μm. These dimensions, the pitch calculated from the dimensions, and the like are the same for unevenness in other cross-sectional shapes.

Depending on the combination of the width of the concave portion and the width of the convex portion, how the facet plane is formed in the growing GaN-based crystal can be changed in various ways, but this facet plane bends the propagation of dislocations. Anything that can be made enough
In a preferred embodiment, as shown in FIG. 2B, the crystal units 21 and 22 grown from each unit reference plane have a mountain shape where both facet planes completely intersect at the top without having a flat portion at each top. (A roof shape long in a triangular pyramid or mountain range). With such a facet surface, almost all dislocation lines inherited from the base surface can be bent, and the dislocation density immediately above the dislocation line can be further reduced.
The facet surface formation region can be controlled by changing not only the combination of the width of the unevenness but also the depth d of the concave portion (the height of the convex portion).

As a method of processing the irregularities, for example, a method is used in which patterning is performed in accordance with the mode of the desired irregularities using ordinary photolithography technology, and etching is performed using the RIE technology or the like to obtain the desired irregularities. And the like.

As a method for growing a semiconductor crystal layer on a substrate, HVPE, MOVPE, MBE or the like is preferable. When forming a thick film, the HVPE method is preferable, but when forming a thin film, the MOVPE method or the MBE method is preferable.

The formation of the facet surface can be controlled by the growth conditions (such as gas type, growth pressure, growth temperature, etc.) during the crystal growth. When the partial pressure of NH ₃ is low, the facet of the {1-101} plane is apt to appear in the reduced pressure growth, and the facet surface is easily formed in the normal pressure growth as compared with the reduced pressure. When the growth temperature is increased, the lateral growth is promoted. However, when the growth is performed at a low temperature, the growth in the C-axis direction is faster than in the lateral growth, and the facet surface is easily formed. Although it has been described that the facet shape can be controlled by the growth condition, the facet shape can be controlled depending on the purpose as long as the effects of the present invention are obtained.

In the facet growth method, when growing a GaN-based crystal from the irregularities formed on the crystal substrate, the GaN-based crystal may be directly grown on the crystal substrate, or may be grown on the GaN or Al
A known low-temperature buffer layer such as N, or another known buffer layer may be interposed.

Although the method of embedding irregularities by the facet growth method has been described above, by selecting the dimensions of the irregularities and the crystal growth conditions, general growth that does not mainly include facet structure growth (for example, lateral growth) The unevenness may be buried by (growth with large growth).

Next, an embodiment in which the cross section of the unevenness is formed in a triangular wave shape will be exemplified. This embodiment is particularly useful when using a GaN crystal substrate as the first layer.

As a method of processing the surface of the crystal substrate into irregularities having such a slope, for example, as shown in FIG. 3A, the surface of the GaN substrate 1 is provided with a convex arch having both edges thinned. Is formed in a target pattern such as a stripe shape or a lattice shape, and the gas is etched. It is preferable to use a material which can undergo the gas etching as a material of the resist. By performing the gas etching on the GaN substrate having such a resist R, the exposed region of the GaN substrate is eroded from the beginning, while the thin shoulder portion of the resist is consumed as the etching proceeds. And the etching of the GaN crystal begins with a delay. By shifting the etching start time in this manner, finally, as shown in FIG. 3B, the cross section becomes uneven as a whole close to a triangular wave. The thickest portion of the resist may be removed by the gas etching, but may be left, and in that case, the resist may be removed using a resist-specific remover that does not damage the GaN crystal. Further, it is more effective to finally perform the etching process on the convex portion.

Preferred dimensions of the unevenness having a slope as shown in FIG. 3B are as follows. Asperity pitch is 2μ
m to 40 µm, particularly preferably 2 µm to 20 µm. The amplitude of the unevenness is 0.05 μm to 5 μm, particularly 0.2 μm to 3 μm.
μm is preferred.

As in the facet growth method described above, the arrangement pattern of the unevenness having a slope is a pattern in which dot-like concave portions (or convex portions) are arranged, linear or curved concave grooves (or convex ridges). Are arranged at regular intervals, and a striped uneven pattern is particularly preferable.

Next, as shown in FIG. 3C, the growth of the second layer 2 is started from the entire surface of the irregularities, and the second layer 2 is grown until the irregularities are completely buried. At this time, since the side wall of the groove has a pseudo facet surface, when a GaN-based crystal is grown, dislocation lines are bent with the facet surface as an interface, and a low dislocation portion is formed in the upper layer. The effect is obtained. Moreover, such unevenness not only acts on light in the lateral direction, but also acts strongly as a reflecting surface, which is a preferred embodiment.

Although the etching method is not limited, RIE (Reactive Ion Etc) using an etching gas containing chlorine is used.
hing), the first layer is G
An aN crystal substrate is preferable because it does not leave damage on the crystal surface.

In the above description, in the GaN-based light-emitting device, an example was shown in which the concavo-convex structure of the facet growth method was used also as concavities and convexities for light in the horizontal direction. An embodiment in which irregularities only for light are separately provided may be adopted.

Next, the embodiment (II) will be described. FIG. 1B is a diagram illustrating a GaN-based LED as a structural example of the light emitting device according to the above-described embodiment (II), in which a GaN-based LED is formed on a surface of a crystal layer (crystal substrate in FIG. A first GaN-based crystal (hereinafter, also referred to as a “first crystal”) 10 is grown so as to form irregularities while forming a facet structure, and at least a convex portion (in the example of FIG. 4, , The first crystal 10 itself)
The second G having a different refractive index from the first GaN-based crystal
An aN-based crystal (hereinafter, also referred to as “second crystal”) 20 is grown, thereby forming an uneven refractive index interface, and the same operation and effect as in the above-described embodiment (I) can be obtained.

In the embodiment (II), when the first crystal is grown so as to form irregularities, the composition is changed to another GaN-based crystal to change the refractive index, that is, the first crystal is flattened only. It is important that they do not grow until they grow. The change in the refractive index (change in composition) may be a step-like change or a continuous change as seen in a distributed index waveguide.

The method of growing the first crystal with irregularities is not limited, but the object of the present invention can be suitably achieved by growing while forming a substantially facet structure or forming a pseudo facet structure. It can be grown as the resulting irregularities. The irregularities referred to here are not only wavy irregularities in which the convex portions are continuously adjacent to each other, but also FIGS.
As shown in (c), the convex first crystals 10 may be discretely arranged, and another substance may be present between them as concave portions.

The shape of the unevenness due to the facet growth of the first crystal is not limited. For example, a trapezoidal shape having a flat portion at the top of the convex portion may be used. In order to obtain a sufficient amount, as described in the above embodiment (I), the crystal units grown from each unit reference plane completely intersect at both apex surfaces without a flat portion at each apex. The shape of a mountain shape (a triangular pyramid or a roof shape long in a mountain range) is preferable.

In the embodiment (II), any method may be used as long as the first crystal can be made uneven.
When the first crystal has irregularities, the second crystal may be grown so as to cover the irregularities and form an irregular refractive index interface.

As a method for growing a GaN-based crystal in a concavo-convex manner, particularly, facet growth (or similar growth)
Is preferred. For this purpose, there is a method of dimensionally limiting a crystal growth region on a crystal layer surface serving as a basis for crystal growth. For example, as in the facet growth method described in detail above, a method of processing irregularities on the surface of a crystal layer serving as a basis for crystal growth (FIG. 1B, FIG.
5 (a), 6 and 7), a method of providing a mask pattern in which GaN-based crystal growth cannot grow on a specific region on the surface of a crystal layer serving as a basis for crystal growth (FIG. 5 (b)), crystal growth (FIG. 5 (c)), etc., in which a specific region on the surface of the crystal layer, which is the basis of the above, is subjected to a surface treatment capable of suppressing GaN-based crystal growth. By these methods, the first crystal grows to have irregularities.

As described above, as shown in FIG. 4, concave and convex concave portions are formed based on the facet growth method.
As shown in FIG. 5A, the first crystal 10 is facet-grown exclusively from only the upper surface of the convex portion, and then the second crystal 20 is not only substantially filled with the N-type crystals 10 and 20. By switching, the lateral growth may be performed on the concave portion, and the concave portion may be left as a cavity. Further, in the above embodiment (I), the unevenness having the slope described as an example in FIG. 3 may be used. This is a mode in which, as shown in FIG. 7, the first crystal 10 is grown on unevenness having a slope on the crystal substrate S, and pseudo facet growth is caused, and then the second crystal 20 is switched. .

As the above method, as shown in FIG. 5B, various lateral growth methods using a conventionally known mask are all applicable. The material of the mask m is S
i, nitrides and oxides of Ti, Ta, Zr, etc., ie, Si
Known mask materials such as O ₂ , SiN _x , TiO ₂ , and ZrO ₂ may be used. As the mask pattern, a known pattern may be referred to, but mainly a stripe pattern, a lattice pattern, and the like are important, and the direction of the boundary between the mask region and the non-mask region is particularly important. . When the boundary line between the mask region and the non-mask region is a straight line extending in the <1-100> direction of the growing GaN-based crystal, the lateral growth rate increases. Conversely, if the boundary between the mask region and the non-mask region is a straight line in the <11-20> direction,
Oblique facets such as the {1-101} plane are easily formed, and facet growth preferable for the present invention is obtained. When the lateral growth method using the mask is performed, the detailed dimensions of the mask and the atmosphere gas (H ₂ , N ₂ , Ar, He)
And the like, and the crystal growth method (HVPE, MOVPE) and the like may be referred to a known technique.
ai et al., Appl. Phys. Lett. 71 (1997) 225.
9. ) Is described in detail.

As the above-mentioned method, for example,
A method of using a residue of SiO ₂ described in JP-A-00-277435 as a mask may be used. As a result, the same operation and effect as those of the above-described mask are exhibited, and it is possible to grow the GaN-based crystal 10 in a facet shape from an untreated region.

In the above embodiment (II), the combination (first crystal / second crystal) of the first crystal grown in a convex shape and the second crystal covering the same is (AlGaN / Ga
N), (AlInGaN / GaN) and the like.
Since AlGaN exists below GaN as the first crystal, GaN of the second crystal corresponds to a core having a high refractive index in the optical waveguide, and AlGaN of the first crystal has a cladding having a lower refractive index. Correspondingly, the function and effect of the present invention are further enhanced, and also effectively function as a reflective layer. The GaN-based crystal (for example, GaN) for embedding the irregularities may be undoped or n-type.

The above are various methods for facet growth of a GaN-based crystal. In any of the methods, even if the third GaN-based crystal for flattening the irregularities is a second crystal. A crystal (including the first crystal) different from the second crystal may be used (the second crystal is continuously grown until it is flattened). Also, the third G
The aN-based crystal may be changed into a multilayer. By selecting the aspect of the third GaN-based crystal, there is a common variation that changes the composition of the GaN-based crystal into a multilayer during or after the growth of the facet structure. Hereinafter, this variation will be described by way of an example of the formation of unevenness by the facet growth method.

In the example of FIG. 4A, the second crystal 20 covering the first crystal 10 is grown as it is until the unevenness is flattened. In the variation, as shown in FIG. First, a second crystal (for example, AlGaN) 20 covering the first crystal (for example, GaN) 10 is formed into a film, and another GaN-based crystal (for example, GaN) 20 having a different refractive index is used.
a grows until it is flattened. FIG.
In the example of (c), the second crystal 20 is grown so as to cover the first crystal 10 in the form of a film, and the first crystal 20a and the second crystal 20b cover the first crystal 10 in order, so that the second crystal 20 has a different refractive index. Different GaN-based crystal films form a multilayer structure.

According to such a multi-layered structure composed of GaN-based crystal films having different refractive indices, the reflectivity can be further improved. For example, the Bragg reflection layer may be formed as a superlattice structure composed of a pair of AlGaN / GaN or the like by optimally designing the film thickness with respect to the emission wavelength.

In the case of a multilayer film structure, there is no limitation on the number of layers of the film, and the structure having a single-layer film as shown in FIG. (Pairs to 100 pairs).

It is not limited at which point the first crystal grown on the irregularities (particularly preferably facet growth) is switched to the second crystal. For example, FIG. As schematically shown, the composition may be changed from the initial growth stage when growing on the uneven surface formed on the substrate S. In the figure, G having different refractive indexes
Hatching is applied to distinguish that the aN-based crystal grows in a multilayer shape and has an irregular shape.

In the embodiment (II), in terms of preferably achieving the object of the present invention, the uneven refractive index interface has a convex portion having a height of 0.05 μm to 10 μm, particularly 0.1 μm to 5 μm.
Are preferred. In addition, the pitch of the uneven refractive index interface is approximately 1 in the conventionally known lateral growth method.
A preferable value is about 10 μm to about 10 μm, particularly about 1 μm to about 5 μm. The pitch of the concavities and convexities obtained by the facet growth method is the same as in the above embodiment (I).

As described above, in any of the above embodiments (I) and (II), the difference between the refractive index of the first layer (first crystal) and the refractive index of the second layer (second crystal) is as follows. The wavelength of the light emitted from the light emitting layer is preferably 0.01 or more, particularly preferably 0.05 or more. Further, the magnitude relationship between the refractive indices of the two is preferably such that the first layer (first crystal) <the second layer (second crystal), whereby the second layer (second crystal) is an optical waveguide. The first layer (first crystal) corresponds to a core having a higher refractive index, and the first layer (first crystal) corresponds to a clad having a lower refractive index.

[0072]

The following is an example of actually manufacturing a GaN-based LED having an uneven refractive index interface according to the above embodiments (I) and (II).

Example 1 In this example, as shown in FIG. 1A, according to the above mode (I), the sapphire substrate was buried by the facet growth method to form a rugged refractive index interface.
N-type LED was actually manufactured.

Stripe patterning (2 μm width, 4 μm period) by photoresist on a C-plane sapphire substrate
m, stripe orientation: longitudinal direction of stripe is <11-20> direction for GaN-based crystal grown on substrate)
Then, the substrate was etched by a RIE apparatus so as to have a rectangular cross section to a depth of 2 μm, thereby obtaining a substrate having a surface in a striped pattern as shown in FIG. At this time, the aspect ratio of the cross section of the stripe groove was 1.

After the photoresist is removed, the substrate is mounted on a MOVPE apparatus, and is heated at 1100 ° C. in a nitrogen gas main component atmosphere.
, And thermal cleaning was performed. Temperature 5
The temperature was lowered to 00 ° C., and trimethylgallium (hereinafter, TMG) was used as a group III material, and ammonia was used as an N material to grow a 30-nm-thick GaN low-temperature buffer layer.

Subsequently, the temperature was raised to 1000 ° C., and TMG and ammonia were flowed as raw materials and silane was flowed as a dopant to grow an n-type GaN layer (contact layer). At this time, as shown in FIG. 2B, the GaN layer grows from a top surface of the convex portion and a bottom surface of the concave portion as a ridge-like crystal having a mountain-shaped cross section and a facet surface, and then a cavity is formed in the concave portion. It was a growth that buried the whole without forming.

In the facet structure growth, when the C-plane of the GaN crystal completely disappears and the top becomes a convex shape, the growth condition is changed to a condition in which lateral growth becomes dominant (such as increasing the growth temperature). Switching was performed, and a GaN crystal was grown from the upper surface of the sapphire substrate to a thickness of 5 μm. In order to obtain a buried layer having a flat upper surface, a 5 μm thick film was required to be grown.

Subsequently, an n-type AlGaN cladding layer, In
A GaN light-emitting layer (MQW structure), a p-type AlGaN cladding layer, and a p-type GaN contact layer are formed in this order.
A 70 nm ultraviolet LED epi-substrate was used, and etching, electrode formation, and element isolation for exposing the n-type contact layer were performed to obtain LED elements.

The output of each LED chip (bare chip state, wavelength of 370 nm, energization of 20 mA) collected on the entire wafer was measured. Further, as Comparative Example 1, an ultraviolet LED chip was formed under the same conditions as above except that no stripe-shaped irregularities were formed on the sapphire substrate (that is, a low-temperature buffer layer was formed on a flat sapphire substrate). An element structure was formed through the device), and the output was measured.
These measurement results are as described below.

Comparative Example 2 In this comparative example, a lateral growth method using a conventionally known mask was applied to reduce the dislocation of the GaN-based crystal layer in Comparative Example 1 described above. Comparative Example 2 is a known structure in which a mask is buried at a stretch with the same composition without changing the composition during growth of the facet structure, and has no uneven refractive index interface due to growth of the facet structure. (II) (particularly, FIG. 5 (b)).

A C-plane sapphire substrate having the same specifications as in Example 1 was loaded into a MOVPE apparatus, and the temperature was raised to 1100 ° C. in a nitrogen gas main component atmosphere to perform thermal cleaning. Reduce the temperature to 500 ° C and use TMG
And flowing ammonia as an N raw material to form a 30-nm thick G
An aN low temperature buffer layer was grown. Then set the temperature to 100
The temperature was raised to 0 ° C., and TMG and ammonia were flowed as raw materials and silane was flowed as a dopant to grow an n-type GaN layer to about 2 μm.

The substrate was taken out of the MOVPE apparatus and striped by photoresist (2 μm width).
m, period 4 μm, stripe orientation: the longitudinal direction of the stripe is <11-20> direction for the GaN crystal), and a 100 nm thick SiO
₂ was deposited. The photoresist was removed by a technique called lift-off to obtain a stripe-shaped SiO ₂ mask.

Again, the MOVPE device is loaded and the n-type Ga
An N-crystal contact layer was grown. The growth conditions were almost the same as in Example 1. After the growth of the GaN crystal from the exposed portion (non-mask region) occurred as a ridge-like crystal having a mountain-shaped cross section and a facet surface, the whole was buried as it was until it became flat. Grow. Approximately 5 μm in the C-axis direction for embedding
It was necessary to grow a GaN crystal having a thickness of.

Subsequently, an n-type AlGaN cladding layer, In
A GaN light-emitting layer (MQW structure), a p-type AlGaN cladding layer, and a p-type GaN contact layer are formed in this order.
A 70 nm ultraviolet LED epi-substrate was used, and etching, electrode formation, and element isolation for exposing an n-type contact layer were performed to obtain LED elements.

The output of each LED chip (bare chip state, wavelength of 370 nm, energization of 20 mA) collected on the entire wafer was measured. The measurement results are as described below.

Embodiment 2 In this embodiment, as shown in FIG. 1B, according to the above mode (II), the facet growth method is used to form AlGaN.
A GaN-based LED was actually manufactured by forming a concave-convex facet structure made of a crystal and embedding it in GaN to form a concave-convex refractive index interface.

In the same manner as in Example 1, irregularities having a stripe pattern were formed on a C-plane sapphire substrate.
Attach to OVPE equipment, 11
The temperature was raised to 00 ° C., and thermal cleaning was performed. The temperature was lowered to 500 ° C., and TMG was
Ammonia was flowed as a raw material to grow a 30-nm-thick GaN low-temperature buffer layer.

Subsequently, the temperature was raised to 1000 ° C., TMG and ammonia were flowed as raw materials to grow a GaN layer of about 100 nm, and then trimethyl aluminum (T
MA) was added to continue the growth, and AlGaN was grown. As shown in FIG. 2B, the growth of the AlGaN / GaN layer occurs from the upper surface of the convex portion and the bottom surface of the concave portion as a ridge-like crystal having a mountain-shaped cross section and a facet surface, and then a cavity is formed in the concave portion. Grow without doing.

In the facet structure growth, AlGaN
When the C-plane of the crystal completely disappeared and became a convex shape with a sharp top, the growth conditions were changed to n-type GaN growth and conditions in which lateral growth was predominant, and the thickness was 5 μm from the top surface of the sapphire substrate. An n-GaN crystal (contact layer) was grown until this.

On the n-type GaN contact layer, an n-type AlGaN cladding layer, In
A GaN light-emitting layer (MQW structure), a p-type AlGaN cladding layer, and a p-type GaN contact layer are formed in this order.
A 70 nm ultraviolet LED epi-substrate was used, and etching, electrode formation, and element isolation for exposing an n-type contact layer were performed to obtain LED elements.

The results of measuring the output of each of the LED chips (bare chip state, wavelength 370 nm, energizing 20 mA) collected on the entire wafer are as described below.

Embodiment 3 In this embodiment, as shown in FIG. 4 (c), according to the above mode (II), an uneven facet structure made of GaN crystal is formed by the facet growth method,
It is covered with 50 pairs of Bragg reflection layers having a superlattice structure of GaN / GaN to form an uneven multilayered refractive index interface.
N-type LED was actually manufactured.

In the same manner as in Example 1, irregularities in a stripe pattern were formed on a C-plane sapphire substrate.
Attach to OVPE equipment, 11
The temperature was raised to 00 ° C., and thermal cleaning was performed. The temperature was lowered to 500 ° C., and TMG was
Ammonia was flowed as a raw material to grow a 30-nm-thick GaN low-temperature buffer layer.

Subsequently, the temperature was raised to 1000 ° C., and TMG and ammonia were flowed as raw materials. As shown in FIG. 4C, the facet surface was formed in a mountain-shaped cross section from the upper surface of the convex portion and the lower surface of the concave portion. Grown as ridge-like crystals.

In the growth of the facet structure, when the C-plane of the GaN crystal completely disappeared and the top became a convex shape, Al _0.2 Ga _0.8 N (37 nm in the C-axis direction) / GaN
(34 nm in the C-axis direction) were grown in 50 pairs, and then the growth conditions were changed to n-type GaN growth and conditions in which lateral growth was predominant, and the thickness was 5 μm from the upper surface of the sapphire substrate.
An n-GaN crystal (contact layer) was grown until this.

On the n-type GaN contact layer, an n-type AlGaN cladding layer, In
A GaN light-emitting layer (MQW structure), a p-type AlGaN cladding layer, and a p-type GaN contact layer are formed in this order.
A 70 nm ultraviolet LED epi-substrate was used. Further, etching, electrode formation and element isolation for exposing the n-type contact layer were performed to obtain LED elements.

The output of each of the LED chips (bare chip state, wavelength 370 nm, energization 20 mA) collected on the entire wafer was measured.

The measurement results (average values) of Examples 1 to 3 and Comparative Examples 1 and 2 are as follows. Example 1: 14 mW. Example 2: 14.5 mW. Example 3: 15 mW. Comparative Example 1: 6 mW. Comparative Example 2: 7 mW. As is clear from the above comparison, by providing the uneven refractive index interface below the light emitting layer, a part of the lateral light that has disappeared inside the element can be extracted to the outside world, and as a light emitting element Was found to improve the output.

[0099]

As described above, by providing an uneven refractive index interface below the light emitting layer, the traveling direction of at least a part of the lateral light generated in the light emitting layer is changed. As a result, the amount of light extracted to the outside world could be increased.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a structural example of a light emitting device according to the present invention. The hatching is partially applied for the purpose of indicating the boundary of the area (the same applies to the following figures).

FIG. 2 is a schematic view showing an example of a crystal growth method for forming a concave-convex refractive index interface in the embodiment (I) of the present invention.

FIG. 3 is a schematic view showing a method for processing the surface of a crystal substrate into unevenness having a slope in the embodiment (I) of the present invention.

FIG. 4 is a schematic view showing an example of a crystal growth method for forming a concave-convex refractive index interface in the embodiment (II) of the present invention.

FIG. 5 is a schematic view showing another example of a crystal growth method for forming an uneven refractive index interface in the embodiment (II) of the present invention.

FIG. 6 is a schematic view showing a variation of the crystal growth method shown in FIGS.

FIG. 7 is a schematic view showing another example of a crystal growth method for forming an uneven refractive index interface in the embodiment (II) of the present invention.

FIG. 8 is a schematic view showing the structure of a conventional GaN-based light emitting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First layer 1a Irregular refractive index interface 2 Second layer 10 First crystal 10a Irregular refractive index interface 20 Second crystal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoichiro Ouchi 4-3 Ikejiri, Itami-shi, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Takashi Tsunekawa 4-3-1 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Wire F term (reference) 5F041 AA03 AA04 CA04 CA05 CA12 CA34 CA40 CA65 CA66 CA74 CA77 5F045 AA04 AB14 AB17 AB18 AC01 AC08 AC12 AC15 AD09 AD14 AF02 AF04 AF09 AF13 BB12 BB16 CA09 DA51 DA53 DA55 DA64 DB06 DB05

Claims (10)

[Claims] An unevenness is formed on a surface of a first crystal layer, and a second crystal layer made of a semiconductor material having a different refractive index from the crystal layer is formed thereon via a buffer layer or directly. A semiconductor light emitting element having a structure in which a semiconductor crystal layer including a light emitting layer is stacked thereon, wherein the semiconductor light emitting element is grown by embedding the irregularities. 2. The semiconductor light emitting device according to claim 1, wherein the second crystal layer and the semiconductor crystal layer thereover are layers composed of a GaN-based semiconductor crystal. 3. The method according to claim 1, wherein the first crystal layer is a crystal substrate, and the second crystal layer is grown while forming a substantially facet structure from an uneven surface processed on the surface of the crystal substrate. 3. The semiconductor light emitting device according to 2. 4. The irregularities processed on the surface of the crystal substrate are irregularities exhibiting a stripe pattern, and the longitudinal direction of the stripe is the <11-20> direction of a GaN-based semiconductor grown by embedding the stripe, or 4. The semiconductor light emitting device according to claim 2, wherein the direction is a <1-100> direction. 5. The semiconductor light emitting device according to claim 1, wherein the cross-sectional shape of the unevenness is a rectangular wave shape, a triangular wave shape, or a sine curve shape. 6. The difference between the refractive index of the first crystal layer and the refractive index of the second crystal layer at the wavelength of light emitted from the light emitting layer is:
The semiconductor light emitting device according to claim 1, wherein the value is 0.05 or more. 7. A first GaN-based semiconductor crystal is grown on a crystal layer surface serving as a basis for crystal growth so as to form irregularities, and covers at least a part of the irregularities to form a first GaN-based semiconductor. A second GaN-based semiconductor crystal having a refractive index different from that of the crystal is grown, and a third GaN-based semiconductor crystal is further grown until the irregularities are flattened. A semiconductor light-emitting device having an element structure in which semiconductor crystal layers including the same are stacked. 8. A structure or a surface treatment for dimensionally limiting a crystal growth region is applied to a surface of a crystal layer serving as a basis for crystal growth, whereby the first GaN-based semiconductor crystal is substantially faceted. The semiconductor light emitting device according to claim 7, wherein the semiconductor light emitting device is grown so as to form irregularities while forming a structure or a pseudo facet structure. 9. A structure or a surface treatment for dimensionally limiting a crystal growth region is provided on a surface of a crystal layer serving as a basis for crystal growth, or provided on a surface of a crystal layer serving as a basis for crystal growth. 9. The semiconductor light emitting device according to claim 8, wherein the semiconductor light emitting device is a mask pattern capable of lateral growth, or a surface treatment applied to a specific region of a crystal layer surface serving as a basis for crystal growth to suppress GaN-based crystal growth. 10. A second GaN-based semiconductor crystal is grown so as to cover at least the projections among the irregularities of the first GaN-based semiconductor crystal, and further covers the third GaN-based semiconductor crystal. In a semiconductor light emitting device having a device structure in which a semiconductor crystal is grown until the unevenness is flattened and a semiconductor crystal layer including a light emitting layer is stacked thereon, the second GaN-based semiconductor crystal has a multilayer film structure. The semiconductor light-emitting device according to any one of claims 7 to 9, comprising: