GALLIUM NITRIDE MATERIALS AND METHODS
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 . A method of producing a semiconductor material comprising:
forming a compositionally-graded transition layer over a silicon substrate; and
forming a gallium nitride material layer over the transition layer.
2 . The method of claim 1 , wherein the composition of the transition layer is graded continuously across the thickness of the layer.
3 . The method of claim 1 , wherein the transition layer comprises an alloy of gallium nitride selected from the group consisting of Al x In y Ga (1-x-y) N, In y Ga (1-y) N, and Al x Ga (1-x) N.
4 . The method of claim 1 , wherein the concentration of gallium in the transition layer is graded.
5 . The method of claim 3 , wherein the value of x decreases in a direction away from the silicon substrate.
6 . The method of claim 3 , wherein the transition layer comprises Al x Ga (1-x) N.
7 . The method of claim 1 , wherein the transition layer comprises a superlattice including a series of alternating Al x In y Ga (1-x-y) N/Al a In b Ga (1-a-b) N layers.
8 . The method of claim 1 , wherein the gallium nitride material layer comprises GaN.
9 . The method of claim 1 , wherein the gallium nitride material layer comprises Al x In y Ga (1-x) N.
10 . The method of claim 1 , further comprising processing the semiconductor material to form at least one semiconductor device.
11 . The method of claim 1 , wherein the gallium nitride material layer has a crack level of less than 0.005 μm/μm 2 .
12 . The method of claim 1 , wherein the gallium nitride material layer has a crack level of less than 0.001 μm/μm 2 .
13 . The method of claim 1 , wherein the gallium nitride material layer is substantially free of cracks.
14 . The method of claim 1 , wherein the gallium nitride material layer is monocrystalline.
15 . The method of claim 1 , further comprising forming an intermediate layer over the silicon substrate and under the transition layer.