JPH11163401A - Gan-based semiconductor light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN-based light-emitting device having superior light- emitting characteristic by preventing reduction in the crystallinity of a Bragg reflection layer and thus preventing reduction in the reflectance. SOLUTION: A multilayered body S, including a light-emitting layer S4, is formed by sequentially growing layers made of GaN-based crystal on a base substrate 1 as a lowermost layer, and electrodes X and Y are formed thereon, thus producing a GaN-based light-emitting device. At this time, a mask layer M, a dislocation line control layer S1 covering the mask layer, and a Bragg reflection layer B1 are provided between the base substrate 1 and the light- emitting layer S4. The Bragg reflection layer B1 is provided on a layer side which is higher than the dislocation line control layer S1, thus improving reduction in crystallinity due to the dislocation line. The dislocation line control layer S1 is a GaN-based crystal layer, having a non-mask region as a growth start surface and is formed by having a crystal grown, until it covers the upper surface of the mask layer M.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN-based semiconductor light-emitting device, and more particularly to a GaN-based semiconductor light-emitting device, in which a low-dislocation region is formed in a laminate by providing a mask layer in the laminate. The present invention relates to a light emitting device having a structure in which a Bragg reflection layer is combined.

[0002]

2. Description of the Related Art A GaN-based semiconductor light emitting device (hereinafter referred to as "Ga
The N-type light-emitting element is also described as a semiconductor light-emitting element using a GaN-based crystal material, and has been actively researched in recent years when a high-brightness diode (LED) has been realized. In addition, reports of room temperature continuous oscillation of semiconductor lasers have been heard. A general method for fabricating these GaN-based light-emitting devices uses a procedure in which a single crystal of sapphire is used as a substrate, a buffer layer is grown thereon at a low temperature, and then a light-emitting portion made of a GaN-based crystal is formed. ing.

[0003]

When a GaN-based crystal layer is grown on a crystal substrate, as in other semiconductors, dislocation occurs when the lattice constant of the substrate and the GaN-based crystal is not matched (lattice mismatch). And other defects. Dislocations also occur due to factors such as contamination of impurities and distortion at the interface of the multilayer film. These dislocations are inherited to the upper layer side even if the thickness of the crystal layer increases as the crystal layer grows, and become continuous defect portions called dislocation lines (threading dislocations).

In a GaN-based light-emitting device, particularly a device using a sapphire crystal as a substrate, the dislocation density is 10% because of a large lattice mismatch between the substrate and the GaN-based layer.
It is known to be more than ¹⁰ cm ^-2 . These dislocations generated at high density also become dislocation lines and propagate to the upper layer even when forming a stacked structure of a GaN-based light emitting element. Since the dislocation is a crystal defect, the light emitting layer acts as a non-light emitting recombination center in the light emitting layer or acts as a current path to cause a leakage current, thereby causing a problem of a deterioration in light emitting characteristics and life characteristics.

On the other hand, as one of the methods for improving the external quantum efficiency of a GaN-based light emitting device, there is a method of providing a Bragg reflection layer. In this method, light is extracted from one of the lower layer side and the upper layer side of the stacked body constituting the light emitting element, and of the light emitted from the internal light emitting layer,
In this method, light traveling toward the side opposite to the side from which light is extracted is reflected by the Bragg reflection layer to the side from which light is extracted, thereby reducing loss.

[0006] When a Bragg reflection layer is provided in a laminate constituting a GaN-based light emitting device, the Bragg reflection layer is also Ga
Since the multilayer structure is made of an N-based crystal, there are many dislocation lines inside the Bragg reflection layer. For this reason, there has been a problem that crystallinity is reduced and a desired reflectance cannot be obtained.

In view of the above problems, an object of the present invention is to provide a GaN
G with excellent light emission characteristics by improving the crystallinity of the Bragg reflection layer provided in the light emitting device
An object of the present invention is to provide an aN-based light emitting device.

[0008]

The GaN-based light-emitting device of the present invention has the following features. (1) A base substrate on which a GaN-based crystal can grow with the C axis as a thickness direction is a lowermost layer, and a plurality of layers including a GaN-based crystal and including a light-emitting layer are sequentially grown and stacked to form a stacked body. A semiconductor light-emitting device having a configuration in which a p-type electrode and an n-type electrode are provided, wherein a mask layer, a layer covering the mask layer, and a Bragg reflection layer are provided between the base substrate and the light-emitting layer. Are provided so that the Bragg reflection layer is the uppermost layer among them, and the mask layer is partially formed on the upper surface of the layer on which the mask layer is provided so as to form a mask region and a non-mask region. And the material of the mask layer is substantially G from its own surface.
The layer that covers the mask layer is a GaN-based crystal layer formed by growing a crystal until it covers the upper surface of the mask layer, using the non-mask region as a starting surface for growth.
aN-based semiconductor light emitting device.

(2) The layer covering the mask layer is a layer formed while controlling the ratio between the growth rate in the C-axis direction and the growth rate in the direction perpendicular to the C-axis. The control of the speed ratio is based on the mask layer formation pattern, crystal growth method,
The GaN-based semiconductor light-emitting device according to the above (1), wherein the GaN-based semiconductor light-emitting device is made by selecting a combination of atmospheric gases during crystal growth.

(3) The pattern for forming the mask layer is a stripe-shaped mask pattern in which strip-shaped mask layers are arranged in stripes, and the longitudinal direction of the stripes corresponds to the GaN-based crystal formed on the base substrate. On the other hand, the dislocation line extending in the <11-20> direction and passing through the non-mask region is bent by a layer covering the mask layer, and the upper portion of the non-mask region is reduced in dislocation. GaN based semiconductor light emitting device.

(4) The pattern for forming the mask layer is a stripe-shaped mask pattern in which strip-shaped mask layers are arranged in stripes, and the longitudinal direction of the stripes corresponds to the GaN-based crystal formed on the base substrate. On the other hand, the dislocation line extending in the <1-100> direction and passing through the non-mask region is not bent by the layer covering the mask layer, and the upper portion of the mask region is reduced in dislocation. GaN-based semiconductor light emitting device.

(5) The GaN-based semiconductor light-emitting device according to (1), wherein the mask layer plays a role of current confinement.

(6) A second mask layer and a layer covering the second mask layer are further provided on the upper layer side of the light emitting layer.
The mask layer is partially provided on the upper surface of the layer on which the mask layer is provided so as to form a mask region and a non-mask region, and the material of the second mask layer is substantially GaN from its own surface. The layer that covers the second mask layer is a material that cannot grow a system crystal, and the layer that covers the second mask layer is a GaN-based crystal layer formed by growing a crystal from the non-mask region as a growth starting surface to cover the upper surface of the mask layer. The GaN-based semiconductor light-emitting device according to 1).

(7) The Ga according to the above (6), wherein one or both of the mask layer provided below the Bragg reflection layer and the second mask layer play a role of current confinement.
N-based semiconductor light emitting device.

(8) The GaN-based semiconductor light emitting device according to the above (5) or (7), wherein the portion of the light emitting layer and the portion of the Bragg reflection layer corresponding to the portion of the current confined by the mask layer are reduced in dislocation. element.

[0016]

In this specification, the lattice plane of a hexagonal lattice crystal such as a GaN-based crystal or a sapphire substrate has four Miller indices (hk
il), for convenience of description,
When an exponent is negative, the exponent is preceded by a minus sign, and the notation method for the negative exponent is the same as that of the general Miller index. Therefore, in the case of a GaN-based crystal, there are six prism surfaces (singular surfaces) parallel to the C-axis. For example, one of the surfaces is (1)
−100), and {1-100} when the six surfaces are grouped as equivalent surfaces. In addition, the above-mentioned Δ1-1
The planes perpendicular to the 00 plane and parallel to the C-axis are equivalently collectively denoted as {11-20}. The direction perpendicular to the (1-100) plane is [1-100], the set of equivalent directions is <1-100>, and the direction perpendicular to the (11-20) plane is [11-20]. The set of equivalent directions is <11
−20>. However, if there is a case where the Miller index is written in the drawing, if the index is negative, the index is indicated by adding a minus sign to the index, and all of the general Miller index notations are followed. The crystal orientations referred to in the present invention are all
The orientation is based on a GaN-based crystal grown on the base substrate with the C axis as the thickness direction.

The "mask region" and the "non-mask region" are both in-plane regions on which a mask layer is formed. The region on the upper surface of the mask layer is regarded as being equal to the mask region, and is used in the description as synonymous. The terms “above and below the mask area” mean above and below perpendicular to the plane of the mask area. The same applies to the upper and lower parts of the non-mask area.

Further, of the p-type electrode and the n-type electrode provided in the GaN-based semiconductor light-emitting element, the electrode provided on the upper layer side with respect to the light-emitting layer is called an upper electrode. On the other hand, the other electrode is called a lower electrode. The upper electrode is provided in an arbitrary shape on the upper surface of a specific layer, and the entire upper surface of the layer is referred to as an upper electrode forming surface.

The inventor of the present invention has previously taken measures shown in FIG. 6 (a) as a countermeasure against cracks in the GaN-based crystal layer caused by differences in lattice constant and thermal expansion coefficient between the GaN-based crystal and the sapphire crystal substrate.
As shown in FIG. 1, a mask layer M patterned in a lattice pattern is provided on the base substrate 1, a GaN-based crystal layer 30 is grown only in the non-mask region 11 where the substrate surface is exposed, and Chip size GaN-based crystal layer 3
It has been proposed to prevent cracks by interspersing zeros (Japanese Patent Application Laid-Open No. 7-273667).

As a result of further studies by the present inventors, when the GaN-based crystal layer 30 grown in a dotted manner is further grown, as shown in FIG. Direction) as well as in the lateral direction (direction perpendicular to the C-axis) from each GaN-based crystal layer 30 toward the mask layer M. In addition, the growth rate in the lateral direction can be as high as that in the thickness direction depending on the crystal orientation in some cases.

When the growth above the mask layer is further advanced, the growth in the thickness direction and the lateral direction is further continued, and the GaN-based crystal completely covers the mask region 12 as shown in FIG. It has been found that a large and thick GaN-based crystal layer 30 having a flat, crack-free and very small number of defects such as dislocations can be obtained by covering and embedding a mask layer.

At this time, the dislocation lines existing in the GaN-based crystal layer 30 are inherited from the base including the base substrate or are generated at the growth interface, and are simply generated from the non-mask region as shown in FIG. It was thought to propagate to.

However, according to the subsequent studies by the present inventors, when a mask layer is formed and crystal growth is performed until the mask layer is buried as described above, the formation pattern of the mask layer, the crystal growth method, and the By selecting a combination of atmospheric gases, they have found that the direction of propagation above the dislocation lines can be controlled in that layer.
With this control method, the inheritance direction of the dislocation lines can be intentionally changed from the non-mask region to above the adjacent mask region or directly from the non-mask region to above any region. became.

As described above, the mask layer and the Ga covering the mask layer
By actively controlling the propagation direction above the dislocation lines using the N-based crystal layer, important dislocations above the mask layer, such as the light-emitting portion and the upper electrode formation surface, can be freely reduced. And the luminous intensity, output, and element life can be improved. In a preferred embodiment, when a mask layer is provided between the two electrodes, a current confinement structure can be formed by the mask layer, and the light-emitting layer can partially emit light. At this time, the luminous intensity can be further improved by controlling the dislocation lines and lowering the central portion of the light emission.

In the present invention, a Bragg reflection layer is provided in the light emitting element stack to emit more light to the outside. However, a mask layer and a GaN-based crystal covering the mask layer are provided below the Bragg reflection layer. The upper and lower relationship of providing a layer is limited. Thereby, it is possible to suppress the crystallinity of each GaN-based crystal layer constituting the Bragg reflection layer from being deteriorated by dislocation lines. Further, similarly to the case of the light emitting layer, the dislocation reduction can be partially performed on the Bragg reflection layer.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light emitting device according to the present invention will be described together with a manufacturing method. As shown in FIG. 1, the light-emitting device of the present invention has a base substrate 1 as a lowermost layer, and a layer composed of GaN-based crystals is sequentially grown and stacked on the base substrate to form a pn junction. A stacked body S including a light emitting layer S4 is formed, and an upper electrode X and a lower electrode Y are provided thereon. In the example of FIG. 1, the light emitting layer S4 is
Two cladding layers S3 with a double heterojunction structure,
The active layer is sandwiched by S5. In the example of FIG. 1, the base substrate 1 is a base sapphire crystal substrate 1.
a buffer layer 1 for improving lattice matching
b, and a GaN-based crystal thin film layer 1c is sequentially formed.

The vertical positional relationship of the p / n type in the example of FIG. 1 is such that the base substrate side is n-type and the upper layer side is p-type because of the processing for forming the p-type and n-type conductivity types. It has become a common thing. Further, an insulator (sapphire crystal substrate) is used for the base substrate, and the n-type GaN layer S
The upper electrode 2 is exposed, and the lower electrode Y is provided on that surface. The surface from which light exits to the outside is the upper surface of the uppermost layer of the laminate, and the Bragg reflection layer is located on the lower layer side. Hereinafter, the p / n type upper / lower relationship is also described when describing other aspects of the light emitting device of the present invention.
The position of the Bragg reflection layer and the electrode arrangement will be described with reference to the same example. However, the p / n type may be upside down, or in the case of a base substrate having conductivity, the lower electrode may be provided on the base substrate.

Between the base substrate 1 and the light emitting layer S4, a mask layer M, a layer S1 covering the mask layer M, and a Bragg reflection layer B1 are provided with the Bragg reflection layer B1 as an upper layer side. The mask layer M is partially provided on the upper surface of the layer on which the mask layer is provided (the base substrate 1 in the example of FIG. 1) so that the mask region 12 and the non-mask region 11 are formed. Also,
The layer S1 that covers the mask layer is a GaN-based crystal layer that is formed by growing a crystal from the non-mask region 11 as a growth starting surface to cover the upper surface of the mask layer M. Hereinafter, the GaN-based crystal layer that covers the mask layer M is referred to as a dislocation line control layer.

The laminated structure forming the GaN-based light emitting device in the example of FIG. 1 has a mask layer M, a dislocation line control layer (n-type GaN layer) S1, a Bragg reflection layer B1, n It has a stacked structure of a p-type GaN layer S2, an n-type AlGaN cladding layer S3, an InGaN light emitting layer S4, a p-type AlGaN cladding layer S5, and a p-type GaN contact layer S6.

The base substrate may be any substrate as long as the GaN-based crystal can be grown with the C-axis in the thickness direction. For example, sapphire, quartz, SiC, etc., which have been widely used for growing GaN-based crystals in the past. May be used. Above all,
A sapphire C-plane, A-plane, or 6H-SiC substrate, particularly a C-plane sapphire substrate is preferred. Also on the surface of these materials,
A buffer layer such as ZnO, MgO, or AlN may be provided to alleviate the difference between the lattice constant and the coefficient of thermal expansion from the GaN-based crystal. Good.

It is important to select a base substrate having a lattice constant as close as possible and a thermal expansion coefficient as close as possible to a GaN-based crystal to be grown. Is desirable. Further, it is preferable that the mask layer has excellent resistance to high heat and etching when forming a thin film of a mask layer described later. From such a point, the base substrate has at least the surface layer of In _x Ga _y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦
1, 0 ≦ Z ≦ 1, X + Y + Z = 1) are preferable. Specifically, on a sapphire substrate, a buffer layer of ZnO or AlN, etc.
Alternatively, a thin film of AlGaN formed sequentially is preferably used. With such a base substrate, the density of dislocations newly generated in the GaN-based crystal grown on the base substrate can be suppressed low, and good crystallinity can be obtained.

[0032] GaN based crystal is used for the material of each layer of the laminate, wherein _{In X Ga Y Al Z N (} 0 ≦ X ≦ 1,0 ≦ Y
≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1). In particular, GaN, InGaN, and the like are useful as GaN-based light-emitting elements.

The number of layers of the laminate is not limited. Known layers such as two layers with a simple pn junction structure and three layers with a double hetero junction structure can be mentioned as examples of only layers directly related to the light emission mechanism in the laminate.
As a form of the light emitting layer, a SQW (Sing
le Quantum well), MQW (Multi Quantum well), quantum dots, and the like. In addition to the light emission-related layer, the Bragg reflection layer, and the dislocation line control layer, as shown in FIG.
6 and a layer including a mask layer for performing current confinement on the upper layer side of the light emitting layer as shown in FIG. 2 and a Bragg reflection on the upper side as shown in FIG. Various functional layers may be added, such as forming a resonator by adding layers.

The Bragg reflection layer is located below the light emitting layer and reflects light emitted from the light emitting layer to the lower layer side.
The light is emitted to the outside world without any loss. The Bragg reflection layer is a known reflection layer, and has a structure in which layers made of materials having different refractive indices are stacked in multiple layers so as to form multiple interfaces.
Among them, a multilayer structure composed of a GaN-based crystal is preferred. In particular, two layers of G forming the superlattice
It is preferable that a pair of aN-based crystal layers is stacked as many as a desired number of layers because of high reflectance.

The mask layer is substantially free of its own surface.
A material that cannot grow a GaN-based crystal is used. like this
Examples of such a material include an amorphous body.
Nitrides such as Si, Ti, Ta, Zr, etc.
Oxide, ie, SiO_Two, SiN_X, SiO_1-XN_X,
TiO_Two, ZrO_TwoEtc. are exemplified. Particularly excellent in heat resistance
Si that is relatively easy to form and etch
N_XOr SiO_1-XN _XA membrane can be suitably used. Also,
As shown in FIG. 2, a second mask is further formed on the mask layer M.
Current layer by providing a mask layer and stopping the propagation of dislocation lines
In this case, the material of the mask layer can stop the propagation of dislocation lines.
Anything can be used.

The mask layer is formed, for example, by vacuum evaporation, sputtering,
After the substrate is formed so as to cover the entire surface of the substrate by a method such as CVD, the photosensitive resist is patterned by a usual photolithography technique, and a part of the substrate is exposed by etching. Although the thickness is not limited, it is usually about 50 nm to 500 nm.

By providing the mask layer, of the dislocation lines propagated from the lower layer side, at least those having reached the mask region can be stopped by the mask layer itself. On the other hand, among the dislocation lines that have propagated from the lower layer side, those that have reached the non-mask region further propagate to the upper layer side. A method of positively controlling the propagation direction of the dislocation line propagating to the upper layer side by the dislocation line control layer will be described below.

The GaN-based crystal layer serving as a dislocation line control layer starts crystal growth from a non-mask region on the surface on which the mask layer is provided. At this time, when growing the GaN-based crystal,
By controlling the ratio of the growth rate in the C-axis direction to the growth rate in the direction perpendicular to the C-axis of the GaN-based crystal, the morphology of the crystal surface when the crystal grows higher than the mask layer can be changed. Broadly speaking, it can be changed as in the following (1) and (2).

(1) If the ratio of the growth rate in the C-axis direction is increased, the morphology of the crystal surface first becomes a pyramid as shown in FIG. By growing in this manner, the propagation of the dislocation lines L can be bent from above the non-mask region to above the adjacent mask region. When the crystal growth is further continued, as shown in FIG. 4B, the crystals from the adjacent mask regions merge and head toward a flat upper surface state. At this time, the dislocation lines are directed upward along the confluence of the crystals, and the dislocations can be reduced above the non-mask region.

(2) If the ratio of the growth rate in the direction perpendicular to the C-axis is made larger, the surface morphology during crystal growth will be as shown in FIG.
As shown in (a), the top surface grows like a trapezoid with a flat top. By growing in this manner, the dislocation lines L can be propagated upward as shown in FIG. In this case, if the crystal growth is further continued, FIG.
As shown in (b), the crystals from the adjacent mask regions merge, the state of the flat upper surface is maintained, and the thickness of the crystal layer increases. At this time, the dislocation line continues upward as it is, and the dislocation above the mask region can be reduced.

Factors for controlling the ratio of the growth rate in the C-axis direction (thickness direction) to the growth rate in the direction perpendicular to the C-axis (lateral direction) are the formation pattern of the mask layer and the crystal growth. Method and atmosphere gas during crystal growth, and how to combine them is important. By the selection, the dislocation line control layer grows as shown in (1) and (2) above, and as a result, the propagation direction of the dislocation line can be selected.

In a mask forming pattern for controlling the direction of propagation of dislocation lines, the direction of the outline of the mask region, that is, the direction of the boundary between the mask region and the non-mask region is important. The boundary line between the mask region and the non-mask region is set to <11-2.
0> direction, a facet plane of {1-
The 100 ° plane is secured as a plane that grows in the lateral direction beyond this boundary line, and the growth rate in the lateral direction is reduced. Since the growth rate in the C-axis direction is faster than the lateral growth rate,
Oblique facets such as the 101 ° plane are easily formed. Therefore, a pyramid-like shape is first formed and then flattened as in (1) above. For this reason, a certain thickness is required for flat embedding.

Conversely, when the boundary between the mask region and the non-mask region is a straight line extending in the <1-100> direction, Ga
The {11-20} plane of the N-based crystal is secured as a plane that crosses this boundary line and grows laterally along the upper surface of the mask layer. The {11-20} plane is an off-facet plane, and therefore has a higher G than the {1-100} plane which is a facet plane.
The aN-based crystal grows at high speed in the lateral direction as described in (2) above. When the lateral growth rate is increased, it is difficult to form oblique facets such as the {1-101} plane. As a result, flat embedding can be thinner than <11-20>.

An example of a pattern that most clearly shows the effect of the mask pattern is a stripe-shaped mask pattern. The stripe-shaped mask pattern is a pattern in which strip-shaped mask layers are arranged in stripes. Therefore, the band-shaped mask regions and the band-shaped non-mask regions are alternately arranged. The longitudinal direction of the stripe (that is, each band) is the direction of the boundary between the mask region and the non-mask region. In the example of FIG. 2, the mask layer is formed as a stripe-shaped mask pattern, and the longitudinal direction of the stripe is set to <1-10
0> direction. The mask pattern is not limited to a stripe pattern, and may be an arbitrary pattern in consideration of a boundary line.

As the crystal growth method, HVPE, MOCV
D. In particular, when a thick film is formed, HVPE having a high growth rate is preferable.
VD is preferred.

The atmosphere gas includes H ₂ , N ₂ , Ar, He and the like, but H ₂ and N ₂ are preferably used to control the growth rate. When growth is performed in an H ₂ -rich atmosphere gas, the growth rate in the C-axis direction increases. In particular, the direction of the boundary line between the mask region and the non-mask region is set to <11-2.
In a combination of straight lines in the 0> direction (slow in the horizontal direction), as shown in (1), a remarkable pyramid shape is first formed and then flattened. For this reason, a certain thickness is required for flat embedding.

On the other hand, when the growth is performed in an N ₂ -rich atmosphere gas, the growth rate in the C-axis direction is lower than in the H ₂ -rich atmosphere, so that the lateral growth rate is relatively higher. . When the growth in the lateral direction is made faster by the combination with the mask pattern, the above-mentioned mode (2) is obtained, and the dislocation line can be propagated upward as it is.

Crystal growth by MOCVD is often performed mainly in an H ₂ -rich atmosphere. For example, as group III gas, carrier gas hydrogen 10 (L) + organic metal bubbling hydrogen 100 (cc). Carrier gas hydrogen 5 (L) + ammonia 5 (L) as group V gas. in this case,
The hydrogen concentration is 75%, which is an example of H ₂ rich. In this case, the nitrogen concentration is 0%.

In terms of crystal growth by MOCVD, the nitrogen concentration when the group III carrier gas is changed to nitrogen is about 50%. The nitrogen concentration when only the group V carrier gas is changed to nitrogen is about 25%. Therefore, in the present invention, the crystal growth by MOCVD, the nitrogen concentration and N ₂ rich over about 25%.

FIGS. 2 and 3 show other structural examples of the GaN-based light emitting device according to the present invention. The example of FIG. 2 is the same as that of FIG. 1 from the base substrate 1 to the double hetero junction structure (S3 to S5), but the structure of the upper layer is different. That is, p-type Al
On the upper surface of the GaN cladding layer S5, a second mask layer M2
Is formed, and the p-type GaN contact layer S6 is a layer covering the mask layer M2. The second mask layer M2 is
It constitutes a current confinement structure. The upper electrode X is provided at a position that avoids a portion above the portion where the current is confined and does not hinder the light emitted from the portion S41, which is the center of light emission, due to the current constriction from going to the outside.

In the light emitting layer, the portion S41 corresponding to the current confinement is reduced in dislocation by the lower mask layer M, and the light emitting efficiency is improved. Further, the second mask layer M2 also functions as a layer for stopping the dislocation lines L,
As a result, the region where the upper electrode X is formed is reduced in dislocation, and a reduction in the element life due to the electrode material entering the dislocation line is suppressed.

In the example of FIG. 3, the second Bragg reflection layer B2 is provided on the upper layer side of the light emitting layer S4, and the lower Bragg reflection layer B2 is provided on the lower layer side.
This is an example in which a resonator is formed together with the semiconductor laser 1 to form a surface-emitting type semiconductor laser. Bragg reflection layer B to form resonator
Although it is necessary to consider the thickness of the layer between B1 and B2, the laminated structure from the base substrate 1 to the layer S6 covering the mask layer M2 is basically the same as that of the LED in FIG. In the example of FIG.
6, a second Bragg reflection layer B2 is further provided,
An upper electrode X is provided thereon. The upper electrode X is
The laser light is provided at a position that does not prevent the laser light from going to the outside world. Bragg reflection layers B1, B2 constituting a resonator
For example, for example, two layers of GaN layer / AlN layer are
Pairs, each of which is laminated by the number of pairs necessary for resonance and emission, are exemplified.

With such a structure, the dislocation of the Bragg reflection layer can be partially reduced to improve the deterioration of crystallinity, and that portion can be used for resonance, and the loss of reflection can be reduced. Further, similarly to the effect in the example of FIG. 2, the central portion S41 of light emission is reduced by the mask layer M to improve the light emission efficiency, and the region where the upper electrode X is formed is reduced by the second mask layer M2. And the reduction in element life is suppressed.

[0054]

Example 1 In this example, a GaN-based LED having the configuration shown in FIG. 1 was actually manufactured. [Formation of Base Substrate] As shown in FIG. 1, a sapphire C-plane substrate was used as the most basic crystal substrate 1a. First, this sapphire C-plane substrate is placed in a MOCVD apparatus,
The temperature was raised to 1100 ° C. in a hydrogen atmosphere, and thermal etching was performed. Thereafter, the temperature was lowered to 500 ° C., and trimethylaluminum (hereinafter referred to as “TMA”) as an Al raw material and ammonia as a N raw material were flown.
Is grown to a thickness of 30 nm, and the temperature is further increased to 1000 ° C., and trimethylgallium (TMG) is
Ammonia was flowed as a raw material to grow the GaN layer 1c to 3 μm, thereby obtaining the base substrate 1.

[Formation of Mask Layer] This sample was subjected to MOCVD.
Take out from the equipment, 100n thickness by sputtering equipment
A m-shaped striped SiO ₂ mask layer M was formed. The longitudinal direction of the mask layer M was formed to be <1-100> with respect to the crystal orientation of the Bragg reflection layer.

[Formation of dislocation line control layer]
Placed in a VD apparatus, heated to 1000 ° C. in a nitrogen atmosphere, flowd TMG, ammonia and silane as a dopant material, and grown an n-type GaN crystal to 5 μm so as to cover the upper surface of the mask layer. (N-type GaN layer) S
1 was obtained.

[Formation of Bragg reflection layer] GaN layer / Al
The Bragg reflection layer B1 was formed by laminating 20 pairs of the two N layers as one pair, each layer having a thickness of 1/4 of the emission wavelength. MOCVD was used to form each layer.

[Formation of n-type GaN layer] TMG, ammonia and silane were flowed as a dopant raw material, and an n-type GaN layer S2 was grown to 2 μm.

[Formation of Double Heterojunction Structure] TMA,
TMG, ammonia, and silane as a dopant material were flowed to grow the n-type AlGaN cladding layer S3 to 0.8 μm. Next, the growth temperature was lowered to 700 ° C. under the condition that the growth atmosphere gas was changed from hydrogen to nitrogen and ammonia was flowed. After the temperature was stabilized at 700 ° C., trimethyl indium (TMI), TMG, and ammonia were flowed as an In material, and an InGaN active layer S4 was grown to 3 nm. At this time, bubbling of TMG and TMI was performed with nitrogen. Thereafter, the temperature was raised to 1000 ° C., the growth atmosphere gas was changed from nitrogen to hydrogen, TMG, TMA, ammonia, and biscyclopentadienyl magnesium (Cp2Mg) were flowed as a dopant material, and a p-type AlGaN cladding layer S5 was formed.
Was grown 0.1 μm to obtain a double hetero junction structure.

[Formation of Contact Layer] Next, TMG, ammonia, and Cp2Mg were flowed as dopant materials to grow the p-type GaN contact layer S6 to 0.5 μm. After the growth, the atmosphere gas was changed to nitrogen and slowly cooled to room temperature.

[Formation of Electrodes] The p-type layer and a part of the double hetero junction structure are removed from the upper surface of the laminate by dry etching of the sample obtained as described above, and the upper surface of the n-type GaN layer S2 is removed. Are exposed, an n-type electrode (lower electrode) Y is formed, and a p-type electrode (upper electrode) X is formed on the uppermost surface of the laminated body to obtain an LED.

As a comparative example with respect to the embodiment 1, a structure having no mask layer M and having a structure in which the dislocation of the Bragg reflection layer B1 is not reduced was manufactured. That is, an LED was formed in exactly the same manner as in Example 1 except that the dislocation line control layer S1 was not provided in Example 1 (the embodiment of FIG. 1). Both L
The ED was mounted on a To-18 stem base, and the output at 20 mA was measured.
W, life 5000 hours, the sample of the comparative example has 2 mW, life 500 hours.
It turned out that it has the characteristic which was excellent in both life.

Example 2 In this example, a GaN-based light emitting device having the configuration shown in FIG. 2 was manufactured. The structure of the laminate is exactly the same as that of Example 1 except for the following points. A mask layer M2 was formed on the upper surface of the p-type AlGaN cladding layer S5, and current confinement was performed on the light emitting layer. Further, the portion that becomes the center of light emission due to the current constriction corresponds to the upper part of the mask region of the lower mask layer M,
That portion was made low dislocation. p-type GaN contact layer S6
Is a layer covering the mask layer M2, similarly to the formation of the dislocation line control layer. In order not to block emission of light to the outside, the upper electrode was formed so as to avoid a portion above the light emission center of the light emitting layer.

When the output of the LED obtained in this example was measured in exactly the same manner as in Example 1, the output was 15 mW and the life was 5000 hr. It turned out to be.

[0065]

According to the GaN-based light emitting device of the present invention, a dislocation line control layer and a Bragg reflection layer are provided. The dislocation line control layer suppresses the decrease in crystallinity of the Bragg reflection layer, and further reduces the dislocations in the light emitting layer, such as the center of light emission and the region where the upper electrode is formed, to improve the deterioration of the characteristics of the light emitting element. doing. Therefore, a GaN-based light-emitting device with improved luminous efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 shows an example of a GaN-based light emitting device according to the present invention, LE.
It is sectional drawing which shows the structure of D. In FIG. 1 and FIG. 2, the ratio of the thickness and width of each layer is exaggerated for the sake of explanation.
It differs from the actual ratio. The electrodes, the light emitting layer, and the mask layer are hatched to distinguish them from other layers. The Bragg reflection layer expresses a multilayer structure.

FIG. 2 is a sectional view showing another example of an LED according to the present invention.

FIG. 3 is a cross-sectional view showing a structure of a semiconductor laser as an example of a GaN-based light emitting device of the present invention.

FIG. 4 is a diagram schematically showing the growth state of a GaN-based crystal and the direction of propagation of dislocation lines when the ratio of the growth rate in the C-axis direction is increased when growing the dislocation line control layer. .

FIG. 5 is a graph showing G when the ratio of the growth rate in the direction perpendicular to the C-axis is increased when growing the dislocation line control layer.
It is a figure which shows the growth state of aN type crystal | crystallization, and the propagation direction of a dislocation line typically.

FIG. 6 is a schematic view showing the growth of a GaN-based crystal on a mask layer.

[Explanation of symbols]

 Reference Signs List 1 base substrate 11 non-mask region 12 mask region B1 Bragg reflection layer M mask layer S laminated body S1 n-type GaN layer (= dislocation line control layer) S2 n-type GaN layer S3 n-type AlGaN cladding layer S4 InGaN active layer S5 p-type AlGaN cladding layer S6 p-type GaN contact layer X upper electrode Y lower electrode

Continued on the front page (72) Inventor Koichi Taniguchi 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Kazuyuki Tadomo 4-chome 3, Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Inside the Itami Works

Claims (8)

[Claims] 1. A base substrate on which a GaN-based crystal can grow with the C axis as a thickness direction is a lowermost layer, and a plurality of layers including a GaN-based crystal and including a light-emitting layer are sequentially grown and stacked to form a stacked body. A semiconductor light-emitting device having a configuration in which a p-type electrode and an n-type electrode are provided, wherein a mask layer, a layer covering the mask layer, A reflective layer provided so that the Bragg reflective layer is the uppermost layer side thereof; and the mask layer is provided such that a mask region and a non-mask region are formed on the upper surface of the layer on which the mask layer is provided. The mask layer is partially provided, and the material of the mask layer is a material from which the GaN-based crystal cannot be grown substantially from its own surface. Until the mask layer top surface is covered. A GaN-based semiconductor light emitting device, which is a GaN-based crystal layer formed by crystal growth. 2. The method according to claim 1, wherein the layer covering the mask layer is a layer formed while controlling a ratio between a growth rate in a C-axis direction and a growth rate in a direction perpendicular to the C-axis. 2. The GaN-based semiconductor light emitting device according to claim 1, wherein the ratio is controlled by selecting a combination of a mask layer formation pattern, a crystal growth method, and an atmosphere gas during crystal growth. 3. A pattern for forming a mask layer is a stripe-shaped mask pattern in which strip-shaped mask layers are arranged in stripes, and the longitudinal direction of the stripes is relative to a GaN-based crystal formed on a base substrate. 2. The GaN-based system according to claim 1, wherein the dislocation lines extending in the <11-20> direction and passing through the non-mask region are bent by a layer covering the mask layer, and the upper portion of the non-mask region is reduced in dislocation. Semiconductor light emitting device. 4. A pattern for forming a mask layer is a stripe-shaped mask pattern in which strip-shaped mask layers are arranged in stripes, and the longitudinal direction of the stripes is in relation to a GaN-based crystal formed on a base substrate. 2. The GaN according to claim 1, wherein the dislocation lines extending in the <1-100> direction and passing through the non-mask region are not bent by the layer covering the mask layer, and the dislocation lines above the mask region are reduced in dislocation. Series semiconductor light emitting device. 5. The GaN-based semiconductor light emitting device according to claim 1, wherein the mask layer plays a role of current confinement. 6. A second mask layer and a layer covering the second mask layer are further provided on an upper layer side of the light emitting layer, and the second mask layer has a mask region and a non-mask layer on an upper surface of the layer on which the mask layer is provided. The second mask layer is a material which is partially provided so as to form a region, and the material of the second mask layer is a material on which GaN-based crystals cannot substantially grow from its own surface. The unmasked area is the starting surface for growth,
The GaN-based semiconductor light-emitting device according to claim 1, wherein the GaN-based semiconductor light-emitting device is a GaN-based crystal layer formed by crystal growth until the mask layer covers the upper surface. 7. A mask layer provided below a Bragg reflection layer and one or both of a second mask layer and
7. The GaN-based semiconductor light-emitting device according to claim 6, which plays a role of current confinement. 8. The light-emitting layer and the Bragg reflection layer corresponding to the current confined by the mask layer,
The GaN-based semiconductor light emitting device according to claim 5, wherein the dislocation is reduced.