JP2010177552A - Nitride semiconductor growth substrate having polar plane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor growth substrate such that a (11-22) plane of sapphire is semipolar not to be influenced by a piezoelectric field as well as a nonpolar plane and thereby while a light emitting element is suitably formed, defects in crystal growth on A, M and R nonpolar planes can be solved. <P>SOLUTION: In the nitride semiconductor growth substrate with the semipolar plane, an AlN, GaN, or AlGaN buffer layer is formed on a principal plane of a sapphire substrate having a semipolar plane. The semipolar plane is the (11-22) plane. After the principal plane of the sapphire substrate having the (11-22) semipolar plane is subjected to unevenness processing, the AlN, GaN, or AlGaN buffer layer is formed. A semiconductor element structure is formed on the AlN, GaN, or AlGaN buffer layer formed on the principal plane of the sapphire substrate having the (11-22) semipolar plane. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nitride-based semiconductor epitaxial substrate that effectively uses a semipolar plane of a sapphire substrate, particularly a (11-22) plane, and a light-emitting device using the same.

  Aluminum nitride (hereinafter referred to as AlN), gallium nitride (hereinafter referred to as GaN), indium nitride (hereinafter referred to as InN), or a mixed crystal thereof, such as aluminum gallium nitride or aluminum gallium indium nitride (hereinafter referred to as AlxGa1). Since nitride semiconductors such as -x-yInyN (referred to as 0≤x≤1, 0≤y≤1, 0≤x + y≤1) can be used for light emitting / receiving elements and electron transit elements, A wide range of research has been conducted on crystal growth and application to semiconductor devices, and some light-emitting diodes and laser diodes have already been put into practical use.

  By the way, in the present situation where a large bulk single crystal of a nitride-based semiconductor cannot be provided, in general, (0001) sapphire (hereinafter referred to as C-plane sapphire) is adopted as an epitaxial substrate. There are a vapor phase growth (MOVPE) method, a molecular beam epitaxy (MBE) method, a halide vapor phase epitaxy (HVPE) method, and the MOVPE method is most commonly used in terms of practical use.

  However, in the case of a light-emitting device such as a light-emitting diode or a laser diode, when a C-axis oriented sapphire crystal is used, an active layer composed of a heterojunction, such as a multiple quantum well structure, generates the piezoelectric field and changes the band structure. Accordingly, the recombination probability of carriers is reduced, which prevents improvement in luminance, and it is said that it is difficult to manufacture a high-luminance light-emitting device because there is a limit even if growth conditions are optimized.

  As described above, the problem of the piezo electric field in the nitride-based semiconductor greatly affects the characteristics of the semiconductor device. However, as a crystal growth method in which the problem due to the piezo electric field does not exist, (11-20) orientation (hereinafter referred to as the A-axis) It is already reported in Non-Patent Document 1 that the alignment may be performed) or (10-10) alignment.

  While there is currently no effective method for orienting a nitride-based semiconductor in (10-10) orientation, a method for orienting a nitride-based semiconductor in (11-20) orientation includes a (1-102) sapphire substrate (hereinafter referred to as “1-102”). , R-plane sapphire substrate) is described in Non-Patent Document 2, and a method of growing AlN on a (11-20) 4H—SiC substrate is described in Non-Patent Document 3. However, among these methods, the latter method is not suitable because it is difficult to increase the size and the mass productivity is poor in the current manufacturing technique of the (11-20) 4H—SiC substrate itself.

  On the other hand, the non-polar sapphire substrate can already be manufactured as an 8-inch substrate, and there is no problem of the substrate diameter. Further, considering the fact that a semiconductor device manufacturing process similar to a semiconductor device using silicon can be used, and that it can be applied in conjunction with an SOS (silicon on sapphire) device, the industrial attractiveness is great. Therefore, it was thought that the method of growing a nitride-based semiconductor on a nonpolar sapphire substrate was most advantageous from the viewpoint of mass productivity and cost. When a semiconductor is grown, the large lattice constant difference, a large amount of threading dislocations due to the nonpolarity of sapphire, and stacking faults are introduced, and the steepness necessary for manufacturing a semiconductor device. It has become clear that there is a problem of poor crystal morphology that makes it difficult to form a smooth interface (Patent Document 1).

JP 2006-232640

Japanese Journal of Applied Physics, Vol.39 (2000) 413-416 Japanese Journal of Applied Physics, Vol. 42 (2003) L818-820 Applied Physics Letters Vol. 83, (2003) 5208-5210

  In view of the fact that sapphire has a wurtzite crystal structure similar to that of GaN, the present inventor has intensively studied and as a result, the (11-22) plane is semipolar, and the piezo electric field is similar to that of the nonpolar plane. Accordingly, the present invention has been completed by paying attention to not only being suitable for forming a light emitting element but also capable of solving the disadvantages of crystal growth on nonpolar surfaces of A, M and R.

  The present invention relates to a nitridation having a semipolar plane, characterized in that an AlN, GaN or AlGaN buffer layer is formed on a main surface of a sapphire substrate having a semipolar plane, particularly a (11-22) semipolar plane. It is to provide a physical semiconductor growth substrate.

  The present invention also provides a nitride semiconductor light emitting device in which a semiconductor device structure is formed on an AlN or AlGaN buffer layer formed on a main surface of a sapphire substrate having a (11-22) semipolar plane. It is.

  In the present invention, it is possible to form a semiconductor element structure that is not easily affected by the piezoelectric field. In addition, if the buffer layer is grown in the A-axis direction, crystal defects that are easily affected by the C-axis direction growth can be reduced. Therefore, the lateral growth method is adopted to reduce the defect density to 10exp6 / cm2 or less. Good.

In order to manufacture the nitride semiconductor of the present invention, a sapphire substrate having a (11-22) semipolar plane shown in FIG. 1 is cut out from a sapphire single crystal bulk, or (11−) on a sapphire substrate C plane shown in FIG. 22) making a cut to form a semipolar surface;
Forming an AlN, GaN or AlGaN buffer layer on a main surface having a (11-22) semipolar surface of a sapphire substrate;
It may be performed by a step of forming the nitride semiconductor device structure on the buffer layer.

The AlN, GaN or AlGaN buffer layer is preferably formed by a step of selectively growing laterally on the (11-22) semipolar plane.

The present invention makes it possible to grow a nitride-based semiconductor that has a low threading dislocation density and excellent surface flatness and is not affected by a piezo electric field on a semipolar plane sapphire substrate. An epitaxial substrate capable of producing a diode can be provided.

It is a perspective view explaining a sapphire (11-22) surface. It is sectional drawing which forms a (11-22) surface on a C surface sapphire substrate. It is sectional drawing explaining the semiconductor device formed on the epitaxial substrate of this invention. It is sectional drawing explaining the method of providing an unevenness | corrugation on the semipolar sapphire substrate of this invention, and forming an epitaxial substrate.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
A GaN / GaInN multiple quantum well structure light emitting device in which a GaN layer is formed on a semipolar plane sapphire substrate was fabricated. As shown in FIG. 3, an n-type GaN buffer layer (30 μm) 2, an n-type GaN cladding layer (450 nm) 3, a GaN / InGaN multiple quantum are formed on a sapphire substrate 1 having a semipolar plane as a main surface by MOVPE. A well structure active layer 4, a p-type AlGaN cladding layer (50 nm) 5 and a p-type GaN layer (200 nm) 6 are sequentially stacked. Then, mesa processing by reactive ion etching and formation of the p-side electrode 7 and the n-side electrode 8 are performed to form a light emitting device.

  Selective lateral growth can be used as one method for reducing the threading dislocation density (Applied Physics Letters, Vol. 81 (2002) 1201-1203). As shown in FIG. 4, after the GaN layer 11 is grown by the MOVPE method on the sapphire substrate 1 having the (11-22) plane as a main surface, it is made of SiO 2 by an existing photolithography technique and a wet etching technique. A mask 12 is formed, and then the regrowth GaN layer 13 is regrown by the MOVPE method. By this method, the mask 12 can prevent the threading dislocations from propagating to the regrowth layer, and the threading dislocation density can be reduced.

  In other words, periodic uneven groove processing is performed on the surface of the (11-22) plane sapphire substrate 1 through the mask 12 to form the groove 11c and the terrace 11b. On top of this, a first underlayer 13 and a second underlayer 14 are successively grown, and then a nitride-based semiconductor layer 15 is finally grown. The nitride-based semiconductor layer 15 may be selectively grown in the lateral direction, and a periodic uneven groove structure formed in the semipolar sapphire substrate 1 may be embedded to form the epitaxial substrate 10.

  Next, as the mask 12, a line-and-space mask 12 is formed on the semipolar sapphire substrate 1 by using a photolithography technique and a vapor deposition technique (FIG. 4A).

  Next, a part of the mask opening 11a on the surface of the semipolar sapphire substrate 1 is removed by etching to form a groove 11c. Since the mask part 11b is not etched, it becomes the terrace part 11b, and a periodic uneven groove structure is formed (FIG. 4B).

  Next, the mask 12 is removed from the surface of the semipolar sapphire substrate 1. In this way, the semipolar sapphire substrate 1 having a periodic uneven groove structure is obtained (FIG. 4C).

  Next, a nitride-based semiconductor layer 15 is grown on the semipolar sapphire substrate 1 by the MOVPE method. By controlling the film thickness and composition and sequentially laminating the first underlayer 13 and the second underlayer 14, an A-axis oriented nitride system having a flat surface and relatively good crystallinity is formed thereon. The semiconductor layer 15 can be grown (FIG. 4D).

  The V / III ratio is the ratio of the supply amount of ammonia (hereinafter referred to as NH3), which is a Group V material, to the supply amount of organic metal, which is a Group III material during growth, and the growth rate depends on the V / III ratio. Anisotropy changes. In addition, since it is different from the V / III ratio of the C-axis-oriented nitride-based semiconductor, it is necessary to pay attention so that the crystal of the nitride-based semiconductor layer 15 ensures lateral growth.

As for the size of the periodic concavo-convex groove processing formed on the sapphire substrate, since a large number of threading dislocations are generated in the nitride-based semiconductor layer 15 in the mask portion, the width should be as small as possible. .

  In the mask opening 11a, a groove 11c is formed by etching. The selective lateral growth starts from the side wall, and the threading dislocations propagate in the lateral direction, so that the dislocations extending in the film thickness direction can be reduced, which contributes to the reduction of the threading dislocation density of the nitride-based semiconductor layer 15.

  If the width of the mask opening 11a is too wide, the initial growth domain of the nitride-based semiconductor layer 15 grows also from the bottom of the trench and grows in the film thickness direction, which makes it difficult to reduce the threading dislocation density. In the case of the A-axis-oriented nitride-based semiconductor layer 15 grown on the polar sapphire substrate 1, the groove 11c can be used. This is because, due to the growth orientation dependence, it is more advantageous to promote the growth of the domain that is growing in the selected lateral direction than the growth from the bottom of the groove 11c.

  In addition, the depth of the periodic concavo-convex groove structure on the surface of the semipolar sapphire substrate 4 formed by the etching method should ensure selective lateral growth in order to sufficiently obtain the effect of reducing the dislocation density.

  The A-axis-oriented nitride-based semiconductor 15 grown as described above is excellent in surface flatness, and an improvement in light emission characteristics due to improvement in crystallinity is observed by a photoluminescence method or the like. In this way, the epitaxial substrate 10 is manufactured.

  In the above embodiment, the concavo-convex grooves were formed on the sapphire substrate, but the nitride-based semiconductor layer was formed, and the concavo-convex grooves were periodically formed on the sapphire substrate. Dislocations may be propagated in the lateral direction and dislocations extending in the film thickness direction may be reduced. By doing in this way, it is possible to grow so as to bury the periodic uneven groove structure formed in the nitride-based semiconductor layer.

DESCRIPTION OF SYMBOLS 1 Epitaxial substrate 11a Mask opening part 11b Terrace part 11c Groove part 12 Mask 13 1st foundation layer 14 2nd foundation layer 15 Nitride type semiconductor layer

Claims (7)

  A nitride semiconductor growth substrate having a semipolar surface, wherein an AlN, GaN or AlGaN buffer layer is formed on a main surface of a sapphire substrate having a semipolar surface.   The nitride semiconductor growth substrate according to claim 1, wherein the semipolar plane is a (11-22) plane.   (11-22) The nitride semiconductor growth substrate according to claim 1, wherein an AlN, GaN, or AlGaN buffer layer is formed on the main surface of the sapphire substrate having a semipolar surface, after being subjected to unevenness processing.   (11-22) A nitride semiconductor light emitting device formed by forming a semiconductor device structure on an AlN or AlGaN buffer layer formed on a main surface of a sapphire substrate having a semipolar plane.   3. The nitride semiconductor light emitting device according to claim 2, wherein the n-type nitride semiconductor layer of the semiconductor device structure is formed of a single layer having a threading transition density of 10exp6 / cm <2> or less. Cutting a sapphire substrate having a (11-22) semipolar plane from a sapphire single crystal or forming a (11-22) semipolar plane on a sapphire substrate;
Forming an AlN, GaN or AlGaN buffer layer on a main surface having a (11-22) semipolar surface of a sapphire substrate;
A method of manufacturing a nitride semiconductor light emitting device comprising the step of forming the nitride semiconductor device structure on the buffer layer. (11-22) The epitaxial substrate according to claim 5, further comprising a step of selectively growing an AlN, GaN or AlGaN buffer layer in a lateral direction after performing uneven processing on a semipolar surface. Production method.

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