III-Nitride Semiconductor Structure with Intermediate and Transition Layers
The invention provides semiconductor materials including a gallium nitride material layer formed on a silicon substrate and methods to form the semiconductor materials. The semiconductor materials include a transition layer formed between the silicon substrate and the gallium nitride material layer. The transition layer is compositionally-graded to lower stresses in the gallium nitride material layer which can result from differences in thermal expansion rates between the gallium nitride material and the substrate. The lowering of stresses in the gallium nitride material layer reduces the tendency of cracks to form. Thus, the invention enables the production of semiconductor materials including gallium nitride material layers having few or no cracks. The semiconductor materials may be used in a number of microelectronic and optical applications.
1 - 92 . (canceled)
93 . A semiconductor structure comprising:
a substrate;
an intermediate layer over the substrate, wherein the intermediate layer comprises aluminum nitride, an aluminum nitride alloy, or a gallium nitride alloy;
a transition layer over the intermediate layer, wherein the transition layer comprises two or more Al x In y Ga (1-x-y) N layers with different Al x In y Ga (1-x-y) N compositions, wherein 0≦x≦1 and 0≦y≦1;
a gallium nitride layer over the transition layer.
94 . The semiconductor structure of claim 93 , wherein the substrate comprises a silicon substrate, a silicon-on-insulator substrate, a silicon-on-sapphire substrate, or a SIMOX substrate.
95 . The semiconductor structure of claim 93 , wherein the two or more Al x In y Ga (1-x-y N layers comprise at least one aluminum nitride layer.
96 . The semiconductor structure of claim 93 , wherein the two or more Al x In y Ga (1-x-y) N layers comprise at least one layer that is substantially free of gallium.
97 . The semiconductor structure of claim 93 , wherein the transition layer comprises two or more layers of gallium nitride alloy and two or more aluminum nitride layers.
98 . The semiconductor structure of claim 93 , wherein the transition layer is discontinuously graded.
99 . The semiconductor structure of claim 93 , wherein y=0 and the x value of the two or more Al x In y Ga (1-x-y) N layers is varied across the transition layer.
100 . The semiconductor structure of claim 99 , wherein the x value of the two or more Al x In y Ga (1-x-y) N layers is varied discontinuously across the transition layer.
101 . The semiconductor structure of claim 93 , further comprising a superlattice layer over the substrate.
102 . The semiconductor structure of claim 98 , wherein the superlattice layer is formed between the substrate and the gallium nitride layer.