Semiconductor device and method of fabricating the same

Abstract

A semiconductor device comprises a single crystal substrate, a nucleus formation buffer layer formed on the single crystal substrate, and a lamination layer including a plurality of Al 1-x-y Ga x In y N (0≦x≦1, 0≦y≦1, x+y≦1) layers laminated above the nucleus formation buffer layer. The nucleus formation buffer layer is formed of Al 1-s-t Ga s In t N (0≦s≦1, 0≦t≦1, s+t≦1) and is formed on a surface of the substrate such that the nucleus formation buffer layer has a number of pinholes for control of polarity and formation of nuclei. A method of fabricating a semiconductor device comprises the steps of: forming, above an Al 1-x-y Ga x In y N (0≦x≦1, 0≦y≦1, x+y≦1) semiconductor layer doped with a p-type dopant, a cap layer for preventing evaporation of a constituent element of the semiconductor layer, the cap layer being formed of one of AlN in which a p-type dopant is added and Al 2 O 3 , subjecting the semiconductor layer to heat treatment, and removing at least a part of the cap layer.

1. A semiconductor device comprising:
 a buffer semiconductor layer made of Al 1-s-t Ga s In t N (0≦s≦1, 0≦t≦1, s+t≦1) and having a number of pinholes formed therein;  
 a thermal distortion reducing layer made of Al 1-u-v Ga u In v N (0≦u≦1, 0≦v≦ 1 0<v≦1 , u+v≦1) formed on said buffer semiconductor layer and having a different chemical formula from that of said buffer semiconductor layer,  
 a first cladding layer formed on said thermal distortion reducing layer;  
 an active layer formed on said first cladding layer; and  
 a second cladding layer formed on said active layer.  
 
     
     
       2. The semiconductor device according to  claim 1 , wherein, in said Al 1-u-v Ga u In v N (0≦u≦1, 0≦v≦ 1 0<v≦1 , u+v≦1) for said thermal distortion reducing layer, v is set to be not less than 0.1 and not more than 0.9. 
     
     
       3. A semiconductor device according to  claim 1 , wherein a film thickness of said thermal distortion reducing layer is greater than that of said semiconductor layer. 
     
     
       4. The semiconductor device according to  claim 1 , further comprising a cap layer on said thermal distortion reducing layer to prevent evaporation of In included in said thermal distortion reducing layer. 
     
     
       5. The semiconductor device according to  claim 4 , wherein said cap layer is made of Al 1-x Ga x N (0≦x≦1) and is formed at 500° C. to 800° C. 
     
     
       6. The semiconductor device according to  claim 1 , wherein said first cladding layer is made of Al 1-x-y Ga x In y N (0≦x≦1, 0≦y≦1, x+y≦1). 
     
     
       7. The semiconductor device according to  claim 1 , wherein said thermal distortion reducing layer has a thickness of 50 nm to 1000 nm. 
     
     
       8. A semiconductor device according to  claim 1 , further comprising a single crystal substrate on which said semiconductor layer is formed. 
     
     
       9. A semiconductor laser comprising:
 a first layer;  
 a second layer made of Al 1-u-v Ga u In v N (0≦u≦1, 0≦v≦1, u+v≦1) formed on said first layer,  
 a third layer formed on said second layer;  
 an active layer formed on said third layer; and  
 a fourth layer formed on said active layer,  
 wherein said first layer is formed of Al 1-s-t Ga s In t N (0≦s≦1, 0≦t≦1, s+t≦1)with an average film thickness of 3 nm to 10 nm such that said first layer has a number of pinholes formed among said Al 1-s-t Ga s In t N (0≦s≦1, 0≦t≦1, s+t≦1).  
 
     
     
       10. A semiconductor laser according to  claim 9 , further comprising a single crystal substrate on which said first layer is formed. 
     
     
       11. The semiconductor device according to  claim 1 , comprising:
   a substrate;        said buffer semiconductor layer being formed on said substrate; and        said pinholes comprising exposed portions of said substrate through said buffer semiconductor layer.     
     
     
       12. The semiconductor device according to  claim 1 , wherein:
   said buffer semiconductor layer comprises crystals formed spaced apart; and        said pinholes comprise spaces between said crystals.     
     
     
       13. The semiconductor device according to  claim 1 , wherein:
   said buffer semiconductor layer comprises crystals loosely formed; and        said pinholes comprise spaces between said crystals.     
     
     
       14. The semiconductor device according to  claim 1 , wherein:
   said buffer semiconductor layer consists essentially of an AlGaN material.     
     
     
       15. The semiconductor device according to  claim 1 , wherein:
   said buffer semiconductor layer consists essentially of an AlN material.     
     
     
       16. A semiconductor device comprising:
   a substrate;        crystals formed on said substrate and containing at least Al and N, said crystals being disposed so as to expose portions of said substrate;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said crystals and having a different chemical formula from that of said crystals;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer.     
     
     
       17. The semiconductor device according to  claim 16 , wherein:
   said crystals consist essentially of an AlGaN material.     
     
     
       18. The semiconductor device according to  claim 16 , wherein:
   said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       19. A semiconductor device comprising:
   a substrate;        a buffer layer formed on said substrate and comprising a first layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  and a second layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said first layer and having a different chemical formula from that of said first layer;        a first cladding layer formed over said second layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer,        wherein said buffer layer comprises means for controlling polarity of a growth surface, said growth surface comprising at least a portion of a surface of said substrate.     
     
     
       20. The semiconductor device according to  claim 19 , wherein:
   said means comprises pinholes.     
     
     
       21. The semiconductor device according to  claim 19 , wherein:
   said means comprises a shape of said buffer layer.     
     
     
       22. The semiconductor device according to  claim 19 , further comprising:
   a substrate wherein:        said buffer layer comprises crystals formed on said substrate; and        said means comprises intervals between said crystals exposing said substrate.     
     
     
       23. The semiconductor device according to  claim 19 , wherein:
   said buffer layer consists essentially of an AlGaN material.     
     
     
       24. The semiconductor device according to  claim 19 , wherein:
   said buffer layer consists essentially of an AlN material.     
     
     
       25. The semiconductor device according to  claim 19 , wherein:
   said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       26. A semiconductor device comprising:
   a substrate;        a buffer layer formed on said substrate and made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   );      a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said buffer layer and having a different chemical formula from that of said buffer layer;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer,        wherein said buffer layer comprises means for controlling polarity of a growth surface of said thermal distortion reducing layer, said growth surface comprising at least a portion of a surface of said substrate.     
     
     
       27. A semiconductor device according to  claim 26 , wherein:
   said means comprises pinholes.     
     
     
       28. The semiconductor device according to  claim 26 , wherein:
   said means comprises a shape of said buffer layer.     
     
     
       29. The semiconductor device according to  claim 26 , further comprising:
   a substrate, wherein:        said buffer layer comprises crystals formed on said substrate; and        said means comprises intervals between said crystals exposing said substrate.     
     
     
       30. The semiconductor device according to  claim 26 , wherein:
   said buffer layer consists essentially of an AlGaN material.     
     
     
       31. The semiconductor device according to  claim 26 , wherein:
   said buffer layer consists essentially of an AlN material.     
     
     
       32. The semiconductor device of  claim 26 , wherein:
   said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       33. A semiconductor device manufactured using a process comprising:
   growing a first buffer layer of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  on a surface of a substrate having portions exposing said surface of said substrate;        forming a second buffer layer of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  on said first buffer layer and having a different chemical formula from that of said first buffer layer; and        forming an active layer over said second buffer layer.     
     
     
       34. A device according to  claim 33 , wherein said process comprises:
   growing said first buffer layer at a temperature between  350 ° C. and  800 ° C.     
     
     
       35. A device according to  claim 33 , wherein said process comprises:
   forming said second buffer layer to absorb thermal distortion.     
     
     
       36. A device according to  claim 33 , wherein said process comprises:
   forming said first buffer layer consisting essentially of AlGaN.     
     
     
       37. A device according to  claim 33 , wherein said process comprises:
   forming said first buffer layer consisting essentially of AlN.     
     
     
       38. A device according to  claim 33 , wherein said process comprises:
   forming said second buffer layer consisting essentially of GaN.     
     
     
       39. A device according to  claim 33 , wherein said process comprises:
   forming said first buffer layer as spaced crystals.     
     
     
       40. A semiconductor device comprising:
   a substrate;        crystals formed on said substrate and containing at least Al and N, said crystals being loosely formed on said substrate;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said crystals and having a different chemical formula from that of said crystals;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer.     
     
     
       41. The semiconductor device according to  claim 40 , wherein said crystals consist essentially of an AlGaN material. 
     
     
       42. The semiconductor device according to  claim 40 , wherein said thermal distortion reducing layer consists essentially of a GaN material. 
     
     
       43. A semiconductor device comprising:
   a substrate;        crystals formed on said substrate and containing at least Al and N, said crystals being formed spaced apart;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said crystals and having a different chemical formula from that of said crystals;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer.     
     
     
       44. The semiconductor device according to  claim 43 , wherein said crystals consist essentially of an AlGaN material. 
     
     
       45. The semiconductor device according to  claim 43 , wherein said thermal distortion reducing layer consists essentially of a GaN material. 
     
     
       46. A semiconductor device comprising:
   a substrate;        crystals formed on said substrate and containing at least Al and N, said crystals having intervals therebetween so as to expose said substrate;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said crystals and having a different chemical formula from that of said crystals;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer.     
     
     
       47. The semiconductor device according to  claim 46 , wherein said crystals consist essentially of an AlGaN material. 
     
     
       48. The semiconductor device according to  claim 46 , wherein said thermal distortion reducing layer consists essentially of a GaN material. 
     
     
       49. A semiconductor device comprising:
   a substrate;        a buffer layer comprising a first layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate;        a second layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said first layer and having a different chemical formula from that of said first layer;        a first cladding layer formed over said second layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer,        wherein said first layer comprises pinholes.     
     
     
       50. The semiconductor device according to  claim 49 , wherein said first layer consists essentially of an AlGaN material, and said second layer consists essentially of a GaN material. 
     
     
       51. A semiconductor device comprising:
   a substrate;        a buffer layer comprising a first layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate, and a second layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said first layer and having a different chemical formula from that of said first layer;        a first cladding layer formed over said second layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer,        wherein said first layer comprises crystals formed on said substrate, said crystals comprising intervals therebetween exposing said substrate.     
     
     
       52. The semiconductor device according to  claim 51 , wherein said first layer consists essentially of an AlGaN material, and said second layer consists essentially of a GaN material. 
     
     
       53. A semiconductor device comprising:
   a substrate;        a buffer layer comprising a first layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate, and a second layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said first layer and having a different chemical formula from that of said first layer;        a first cladding layer formed over said second layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer,        wherein said first layer comprises crystals formed spaced apart.     
     
     
       54. The semiconductor device according to  claim 53 , wherein said first layer consists essentially of an AlGaN material, and said second layer consists essentially of a GaN material. 
     
     
       55. A semiconductor device comprising:
   a substrate;        a buffer layer comprising a first layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate, and a second layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said first layer and having a different chemical formula from that of said first layer;        a first cladding layer formed over said second layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer,        wherein said first layer comprises crystals disposed so as to expose portions of said substrate.     
     
     
       56. The semiconductor device according to  claim 55 , wherein said first layer consists essentially of an AlGaN material, and said second layer consists essentially of a GaN material. 
     
     
       57. A semiconductor device comprising:
   a substrate;        a buffer layer comprising a first layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate, and a second layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said first layer and having a different chemical formula from that of said first layer;        a first cladding layer formed over said second layer; and        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer,        wherein said first layer comprises crystals loosely formed on said substrate.     
     
     
       58. The semiconductor device according to  claim 57 , wherein said first layer consists essentially of an AlGaN material, and said second layer consists essentially of a GaN material. 
     
     
       59. A semiconductor device comprising:
   a substrate;        a buffer layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said buffer layer and having a different chemical formula from that of said buffer layer;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer,        wherein said buffer layer comprises crystals formed on said substrate, said crystals having intervals therebetween so as to expose said substrate.     
     
     
       60. The semiconductor device according to  claim 59 , wherein
   said buffer layer consists essentially of an AlGaN material, and        said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       61. A semiconductor device comprising:
   a substrate;        a buffer layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said buffer layer and having a different chemical formula from that of said buffer layer;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer,        wherein said buffer layer comprises crystals formed spaced apart on said substrate.     
     
     
       62. The semiconductor device according to  claim 61 , wherein
   said buffer layer consists essentially of an AlGaN material, and        said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       63. A semiconductor device comprising:
   a substrate;        a buffer layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said buffer layer and having a different chemical formula from that of said buffer layer;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer,        wherein said buffer layer comprises crystals disposed so as to expose portions of said substrate.     
     
     
       64. The semiconductor device according to  claim 63 , wherein
   said buffer layer consists essentially of an AlGaN material, and        said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       65. A semiconductor device comprising:
   a substrate;        a buffer layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said buffer layer and having a different chemical formula from that of said buffer layer;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer,        wherein said buffer layer comprises crystals loosely formed on said substrate.     
     
     
       66. The semiconductor device according to  claim 65 , wherein
   said buffer layer consists essentially of an AlGaN material, and        said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       67. A semiconductor device comprising:
   a substrate;        crystals formed on said substrate and containing at least Al and N;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed to contact said crystals and said substrate and having a different chemical formula from that of said crystals;        a first cladding layer formed over said thermal distortion reducing layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer.     
     
     
       68. The semiconductor device according to  claim 67 , comprising:
   said thermal distortion reducing layer contacting said substrate through intervals between crystals.     
     
     
       69. A semiconductor device comprising:
   a substrate;        a buffer layer comprising a first layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  formed on said substrate and a second layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed to contact said first layer and said substrate and having a different chemical formula from that of said first layer;        a first cladding layer formed over said second layer;        an active layer formed over said first cladding layer; and        a second cladding layer formed over said active layer.     
     
     
       70. The semiconductor device according to  claim 69 , comprising:
   said second layer contacting said substrate through intervals in said first layer.     
     
     
       71. A semiconductor device comprising:
   a buffer semiconductor layer made of Al   1-s-t   Ga   s   In   t   N  (   0 ≦s≦ 1 ,  0 ≦t≦ 1 , s+t≦ 1   )  and having a number of pinholes formed therein;        a thermal distortion reducing layer made of Al   1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  formed on said buffer semiconductor layer and having a different chemical formula from that of said buffer semiconductor layer;        a first cladding layer formed on said thermal distortion reducing layer;        an active layer formed on said first cladding layer; and        a second cladding layer formed on said active layer.     
     
     
       72. The semiconductor device according to  claim 71 , wherein, in said Al 1-u-v   Ga   u   In   v   N  (   0 ≦u≦ 1 ,  0 ≦v≦ 1 , u+v≦ 1   )  for said thermal distortion reducing layer, v is set to be not less than  0 . 1  and not more than  0 . 9 .   
     
     
       73. A semiconductor device according to  claim 71 , wherein a film thickness of said thermal distortion reducing layer is greater than that of said buffer semiconductor layer. 
     
     
       74. The semiconductor device according to  claim 71 , further comprising a cap layer on said thermal distortion reducing layer to prevent evaporation of In included in said thermal distortion reducing layer. 
     
     
       75. The semiconductor device according to  claim 74 , wherein said cap layer is made of Al 1-x   Ga   x   N  (   0 ≦x≦ 1   )  and is formed at  500 ° C. to  800 ° C.   
     
     
       76. The semiconductor device according to  claim 71 , wherein said first cladding layer is made of Al 1-x-y   Ga   x   In   y   N  (   0 ≦x≦ 1 ,  0 ≦y≦ 1 , x+y≦ 1   ). 
     
     
       77. The semiconductor device according to  claim 71 , wherein said thermal distortion reducing layer has a thickness of  50  nm to  1000  nm. 
     
     
       78. A semiconductor device according to  claim 71 , further comprising a single crystal substrate on which said buffer semiconductor layer is formed. 
     
     
       79. The semiconductor device according to  claim 71 , comprising:
   a substrate;        said buffer semiconductor layer being formed on said substrate; and        said pinholes comprising exposed portions of said substrate through said buffer semiconductor layer.     
     
     
       80. The semiconductor device according to  claim 71 , wherein:
   said buffer semiconductor layer comprises crystals formed spaced apart; and        said pinholes comprise spaces between said crystals.     
     
     
       81. The semiconductor device according to  claim 71 , wherein:
   said buffer semiconductor layer comprises crystals loosely formed; and        said pinholes comprise spaces between said crystals.     
     
     
       82. The semiconductor device according to  claim 71 , wherein:
   said buffer semiconductor layer consists essentially of an AlGaN material.     
     
     
       83. The semiconductor device according to  claim 71 , wherein:
   said buffer semiconductor layer consists essentially of an AlN material.     
     
     
       84. The semiconductor device according to  claim 71 , wherein:
   said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       85. The semiconductor device of  claim 71 , comprising:
   a substrate, said buffer semiconductor layer being formed on said substrate.     
     
     
       86. The semiconductor device according to  claim 11 , wherein:
   said buffer semiconductor layer consists essentially of an AlGaN material.     
     
     
       87. The semiconductor device according to  claim 11 , wherein:
   said buffer semiconductor layer consists essentially of an AlN material.     
     
     
       88. The semiconductor device according to  claim 11 , wherein:
   said thermal distortion reducing layer consists essentially of a GaN material.     
     
     
       89. The semiconductor device of  claim 12 , comprising:
   a substrate, said buffer semiconductor layer being formed on said substrate.     
     
     
       90. The semiconductor device of  claim 13 , comprising:
   a substrate, said buffer semiconductor layer being formed on said substrate.