JP2012094896A - Nitride-based semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride-based semiconductor light-emitting element capable of preventing forming a Schottky barrier at the interface between a contact layer and an electrode.SOLUTION: A nitride-based semiconductor light-emitting element LD1 comprises: a GaN substrate 3; a hexagonal gallium nitride-based semiconductor region 5 that is provided on a primary surface S1 of the GaN substrate 3 and includes a light-emitting layer 11; and a p-electrode 21 that is provided on the gallium nitride-based semiconductor region 5 and is composed of a metal. The gallium nitride-based semiconductor region 5 includes a contact layer 17 including strain, and the contact layer 17 contacts the p-electrode. The primary surface S1 extends along a reference surface S5 inclined at a predetermined inclination angle θ from a surface perpendicular to the c-axis direction of the GaN substrate 3, and the inclination angle θ falls within the range from more than 40 degrees to less than 90 degrees or from 150 degrees or more to less than 180 degrees. The gallium nitride-based semiconductor region 5 is lattice-matched to the GaN substrate 3.

Description

  The present invention relates to a nitride semiconductor light emitting device.

  Patent Document 1 discloses the structure of a highly efficient GaN-based optical semiconductor element. A light-emitting element that is an optical semiconductor element of Patent Document 1 includes a plurality of GaN-based semiconductor layers including strained quantum well layers that contain strain. This light-emitting element is formed by sequentially depositing an n-type GaN contact layer, an n-type AlGaN cladding layer, a multiple strain quantum well layer, a p-type AlGaN cladding layer, and a p-type GaN contact layer on a substrate such as sapphire, SiC, or GaN. The Furthermore, an n electrode and a p electrode, which are the respective electrodes, are formed on each of the n-type GaN contact layer and the p-type GaN contact layer. As the multiple strain quantum well layer, a GaInN / GaN multiple strain quantum well layer or a GaInN / GaInN multiple strain quantum well layer is used. The plane orientation of the growth surface of this multi-strain quantum well layer is different from the orientation in which piezoelectrolysis is maximized.

JP-A-11-112029

  The conventional optical semiconductor device includes a p-type GaN contact layer and a p-electrode, and the p-electrode is in contact with the p-type GaN contact layer. In the case of such an optical semiconductor element, p-type GaN has a relatively large work function, so that a Schottky barrier may be formed at the interface between the p-type GaN contact layer and the p electrode. Accordingly, an object of the present invention is to provide a nitride-based semiconductor light-emitting device capable of suppressing the formation of a Schottky barrier at the interface between a contact layer and an electrode.

  The nitride semiconductor light emitting device of the present invention is provided on a GaN substrate, a hexagonal gallium nitride semiconductor region including a light emitting layer provided on the main surface of the GaN substrate, and the gallium nitride semiconductor region. The gallium nitride based semiconductor region includes a contact layer containing strain, the contact layer is in contact with the electrode, and the main surface is a c-axis of the GaN substrate. It extends along a reference plane inclined at a predetermined inclination angle from a plane orthogonal to the direction, and the inclination angle is any of a range greater than 40 degrees and less than 90 degrees, or a range between 150 degrees and less than 180 degrees. The gallium nitride based semiconductor region is lattice-matched to the GaN substrate, and the contact layer is made of p-type doped InGaN or p-type doped InAlGaN, When the contact layer is made of p-type doped InGaN, the In composition ratio of the contact layer is in the range of 1% to 20%, and when the contact layer is made of p-type doped InAlGaN, The Al composition ratio of the contact layer is smaller than a value obtained by multiplying the In composition ratio of the contact layer by 0.33.

  Therefore, according to the nitride-based semiconductor light-emitting device of the present invention, the angle formed by the main surface of the GaN substrate and the surface orthogonal to the c-axis direction of the GaN substrate is in a range greater than 40 degrees and less than 90 degrees, or 150 In the case of a value included in any of the range of not less than 180 degrees and less than 180 degrees, since the GaN substrate and the gallium nitride based semiconductor region are lattice-matched, p-type doped InGaN or p-type doped InAlGaN A compressive stress is generated in the contact layer made of in the direction along the reference plane, and thus a negative piezoelectric field is generated. By such a negative piezoelectric field, the energy band in the contact layer changes in the direction in which the Schottky barrier is reduced. In the case where the contact layer is made of p-type doped InGaN, if the In composition ratio of the contact layer is in the range of 1% or more and 20% or less, for example, in the contact layer having a thickness of 10-50 nm, compressive stress is caused by lattice relaxation. The Schottky barrier of the energy band in the contact layer is reduced without being released. When the contact layer is made of p-type doped InAlGaN, if the In composition ratio of the contact layer is larger than the value obtained by multiplying the Al composition ratio by 0.22, the contact layer is in contact with the GaN substrate. It has compressive stress.

  In the nitride-based semiconductor light-emitting device of the present invention, it is preferable that the tilt angle is in a range of 63 degrees to less than 83 degrees. When the tilt angle is in the range of not less than 63 degrees and less than 83 degrees, the negative piezo becomes maximum, so that the drive voltage is sufficiently reduced.

  In the nitride semiconductor light emitting device of the present invention, the light emitting layer preferably emits light having a peak wavelength within a predetermined range of 500 nm or more. Even in the case of emitting light having a peak wavelength of 500 nm or more, in which the voltage drop in the light emitting layer becomes significant and the driving voltage of the entire device increases, the driving voltage can be reduced according to the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the nitride type semiconductor light-emitting device which can suppress that a Schottky barrier is formed in the interface of a contact layer and an electrode can be provided.

It is a figure for demonstrating the structure of LD which concerns on embodiment. It is a figure for demonstrating the effect of LD which concerns on embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, if possible, the same elements are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 is a diagram for explaining the configuration of the LD 1 according to the embodiment. The LD 1 is a nitride semiconductor light emitting device including a GaN substrate 3, a gallium nitride semiconductor region 5, an insulating film 19, a p electrode 21 and an n electrode 23. The n electrode 23, the GaN substrate 3, the gallium nitride based semiconductor region 5, and the p electrode 21 are sequentially provided along a predetermined z-axis direction.

  The GaN substrate 3 is provided between the n-electrode 23 and the gallium nitride based semiconductor region 5 (particularly the optical confinement layer 7), and is in contact with the n-electrode 23. The GaN substrate 3 has a main surface S1. The main surface S <b> 1 is a surface on the opposite side of the n electrode 23 among the surfaces of the GaN substrate 3. The main surface S1 extends from a surface orthogonal to the c-axis direction of the GaN substrate 3 along a reference plane S5 that is inclined at a predetermined inclination angle θ. The inclination angle θ is included in any of a range greater than 40 degrees and less than 90 degrees, or a range between 150 degrees and less than 180 degrees (40 degrees <θ <90 or 150 degrees ≦ θ ≦ 180). More preferably, it is within the range of 63 degrees or more and less than 83 degrees (63 degrees ≦ θ <83 degrees).

  The gallium nitride based semiconductor region 5 is provided between the GaN substrate 3 and the p-electrode 21 and is in contact with the GaN substrate 3 through the main surface S 1 of the GaN substrate 3. The gallium nitride based semiconductor region 5 is made of a hexagonal gallium nitride based semiconductor and is provided on the main surface S1. The gallium nitride based semiconductor region 5 is lattice-matched to the GaN substrate 3. The gallium nitride based semiconductor region 5 includes a light confinement layer 7, a light guide layer 9, a light emitting layer 11, a light guide layer 13, a light confinement layer 15, and a contact layer 17. The light confinement layer 7, the light guide layer 9, the light emitting layer 11, the light guide layer 13, the light confinement layer 15, and the contact layer 17 are sequentially provided along the z-axis direction on the main surface S1.

  The light confinement layer 7 is provided between the GaN substrate 3 and the light guide layer 9, and is in contact with the GaN substrate 3 through the main surface S1. The light guide layer 9 is provided between the light confinement layer 7 and the light emitting layer 11 and is in contact with the light confinement layer 7. The light emitting layer 11 is provided between the light guide layer 9 and the light guide layer 13 and is in contact with the light guide layer 9. The light emitting layer 11 has a multiple quantum well structure including a plurality of well layers and a plurality of barrier layers, and the light guide layer 9 is in contact with the barrier layer of the light emitting layer 11. The light emitting layer 11 emits light having a peak wavelength within a predetermined range of 500 nm or more (preferably within a range of 500 nm or more and 550 nm or less). The light guide layer 13 is provided between the light emitting layer 11 and the light confinement layer 15 and is in contact with the light emitting layer 11 (particularly the barrier layer).

  The light confinement layer 15 is provided between the light guide layer 13 and the contact layer 17 and is in contact with the light guide layer 13. The contact layer 17 is provided between the light confinement layer 15 and the p-electrode 21, and is in contact with the light confinement layer 15 through the interface S 3 of the contact layer 17. Further, the contact layer 17 is in contact with the p electrode 21. The n electrode 23 is in contact with the GaN substrate 3.

  The optical confinement layer 15 and the contact layer 17 form a stripe-shaped portion 25. The stripe-shaped portion 25 has a convex shape extending in the y-axis direction provided on a part of the surface S7 of the light guide layer 13 (this surface is on the opposite side of the interface with the light emitting layer 11). On the surface S7 of the light guide layer 13, an insulating film 18, a stripe-shaped portion 25, and an insulating film 19 are sequentially arranged along the x-axis direction. The stripe-shaped portion 25 is provided between the insulating film 18 and the insulating film 19 and is in contact with the insulating film 18 and the insulating film 19. The insulating film 18 and the insulating film 19 are in contact with the light guide layer 13 through the surface S7.

  Next, an example of the LD 1 will be described. The main surface S1 of the GaN substrate 3 is a 75-degree off-surface ((20-21) surface) in the m-axis direction. The optical confinement layer 7 is made of InAlGaN (In composition ratio is 3%, Al composition ratio is 14%) or AlGaN (Al composition ratio is 7%) and has a thickness of about 1200 nm. . Both the light guide layer 9 and the light guide layer 13 are made of InGaN (In composition ratio is 3%) and have a thickness of about 100 nm. Each of the plurality of well layers of the light emitting layer 11 is made of InGaN (the composition ratio of In is 30%) and has a thickness of about 3 nm. Each of the plurality of barrier layers of the light emitting layer 11 is made of InGaN (the composition ratio of In is 0 to 3%) and has a thickness of about 10 nm. The light emitting layer 11 emits light in the 520 nm band.

  The optical confinement layer 15 is made of p-type doped AlGaN (Al composition ratio is 7%) or p-type doped InAlGaN (In composition ratio is 3% and Al composition ratio is 14%). And has a thickness of about 400 nm. The contact layer 17 is made of p-type doped InGaN or p-type doped InAlGaN, and has a thickness of about 10 to 50 nm. When the contact layer 17 is made of p-type doped InGaN, the In composition ratio of the contact layer 17 is in the range of 1% to 20%. When the contact layer 17 is made of p-type doped InAlGaN, the In composition ratio of the contact layer 17 is larger than the value obtained by multiplying the Al composition ratio of the contact layer 17 by 0.22. The band gap energy of the optical confinement layer 15 is larger than the band gap energy of the contact layer 17.

Insulating film 19 is made of SiO _2. The p electrode 21 is made of any one of Ni / Au, Pt / Pd, Pd / Au, Al / Ti / Al, Ni / Pt / Au, and Pd / Pt / Au. The n electrode 23 is made of Ti / Al.

  The width of the gallium nitride based semiconductor region 5 in the direction along the reference plane S5 is about 400 μm, and the height in the direction perpendicular to the reference plane S5 is about 100 μm. The stripe-shaped portion 25 has a width in the direction along the reference plane S5 of the gallium nitride based semiconductor region 5 of about 2 μm and a height in the direction perpendicular to the reference plane S5 of about 1 μm.

Next, the outline of the manufacturing method of LD1 which concerns on an Example is demonstrated. First, a gallium nitride based semiconductor region corresponding to the gallium nitride based semiconductor region 5 was formed on the surface of the GaN substrate corresponding to the GaN substrate 3. Next, a portion corresponding to the stripe-shaped portion 25 was formed by dry etching. Next, a SiO ₂ insulating film corresponding to the insulating film 18 and the insulating film 19 was formed by sputtering on the portion removed by the dry etching, and then a p-electrode 21 was formed and divided into a plurality of LDs 1.

  According to LD1 which concerns on the present Example demonstrated above, the angle (inclination angle (theta)) which main surface S1 and the surface orthogonal to the c-axis direction of GaN board | substrate 3 make is the range larger than 40 degree | times and smaller than 90 degree | times, or In the case of a value included in the range of 150 degrees or more and less than 180 degrees, since the GaN substrate 3 and the gallium nitride based semiconductor region 5 are lattice-matched, p-type doped InGaN or p-type doped In the contact layer 17 made of InAlGaN, compressive stress is generated in the direction along the reference plane S5, and thus a negative piezoelectric field is generated. By such a negative piezoelectric field, the energy band in the contact layer 17 changes in the direction in which the Schottky barrier is reduced. Therefore, the operating voltage of LD1 is reduced. Actually, the measured value of the operating voltage of another LD using the contact layer 17a made of p-type doped GaN instead of the contact layer 17 of the LD 1 according to the present embodiment was 10 (volts). The measured value of the operating voltage of the LD 1 according to the example was 6 (volts).

  FIG. 2A shows the band gaps of the optical confinement layer 15 and the contact layer 17. FIG. 2B shows the band of the optical confinement layer 15 and the contact layer 17a of the other LD using the contact layer 17a made of p-type doped GaN instead of the contact layer 17 of the LD 1 according to this embodiment. Indicates a gap. The symbol F in the figure indicates the Fermi level, and the symbol H in the figure indicates the direction of the hole current. As shown in FIGS. 2A and 2B, the band gap of the contact layer 17 of the LD1 according to this embodiment is different from that of the Schottky barrier SB1 of the contact layer 17 of the LD1 according to this embodiment. The contact layer 17a of the LD changes in a direction to be lower than the Schottky barrier SB2.

  Further, when the contact layer 17 is made of p-type doped InGaN, the Schottky barrier of the energy band in the contact layer 17 is reduced when the In composition ratio of the contact layer 17 is 1% or more. When the In composition ratio exceeds 20%, the compressive stress is released by lattice relaxation in the contact layer 17 having a thickness of 10-50 nm, so that the In composition ratio of the contact layer 17 is within the range of 1% to 20%. It was. Further, when the contact layer 17 is made of p-type doped InAlGaN, the Al composition ratio of the contact layer 17 is set so that the contact layer 17 has a compressive stress with respect to the GaN substrate 3. The value was smaller than the value obtained by multiplying the In composition ratio by 0.33. Further, if the tilt angle θ is in the range of 63 degrees or more and less than 83 degrees, the negative piezo is maximized, so that the driving voltage of the LD 1 according to the present embodiment can be sufficiently reduced. Further, if the other LD emits light having a peak wavelength of 500 nm or more, the voltage drop in the light emitting layer 11 becomes remarkable and the driving voltage of the entire LD 1 becomes high. However, the LD 1 according to the present embodiment has a wavelength of 520 nm. Although it emits band light, the driving voltage can be reduced as compared with the other LDs.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  DESCRIPTION OF SYMBOLS 1 ... LD, 3 ... GaN substrate, 5 ... Gallium nitride system semiconductor region, 7 ... Light confinement layer, 9 ... Light guide layer, 11 ... Light emitting layer, 13 ... Light guide layer, 15 ... Light confinement layer, 17 ... Contact layer , S1 ... main surface, S3 ... interface, S5 ... reference plane, 21 ... p electrode, 23 ... n electrode, 25 ... stripe-shaped portion, S7 ... surface, 18, 19 ... insulating film

Claims (2)

A nitride semiconductor light emitting device,
A GaN substrate;
A hexagonal gallium nitride semiconductor region including a light emitting layer provided on the main surface of the GaN substrate;
An electrode made of a metal provided on the gallium nitride based semiconductor region,
The gallium nitride based semiconductor region includes a contact layer containing strain,
The contact layer is in contact with the electrode;
The main surface extends along a reference plane inclined at a predetermined inclination angle from a surface orthogonal to the c-axis direction of the GaN substrate toward the m-axis of the GaN substrate,
The inclination angle is included in a range of 63 degrees or more and less than 83 degrees,
The gallium nitride based semiconductor region is lattice-matched to the GaN substrate,
The contact layer is made of p-type doped InGaN or p-type doped InAlGaN,
When the contact layer is made of p-type doped InGaN, the In composition ratio of the contact layer is in the range of 1% to 20%, and when the contact layer is made of p-type doped InAlGaN, The nitride-based semiconductor light-emitting device, wherein the In composition ratio of the contact layer is larger than a value obtained by multiplying the Al composition ratio of the contact layer by 0.22.   2. The nitride-based semiconductor light-emitting element according to claim 1, wherein the light-emitting layer emits light having a peak wavelength within a predetermined range of 500 nm or more.

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