Boron-containing buffer layer for growing gallium nitride on silicon
View Patent ↗A silicon wafer used in manufacturing GaN for LEDs includes a silicon substrate, a buffer layer of boron aluminum nitride (B x Al 1-x N) and an upper layer of GaN, for which 0.35≦x≦0.45. The BAlN forms a wurtzite-type crystal with a cell unit length about two-thirds of a silicon cell unit length on a Si(111) surface. The C-plane of the BAlN crystal has approximately one atom of boron for each two atoms of aluminum. Across the entire wafer substantially only nitrogen atoms of BAlN form bonds to the Si(111) surface, and substantially no aluminum or boron atoms of the BAlN are present in a bottom-most plane of atoms of the BAlN. A method of making the BAlN buffer layer includes preflowing a first amount of ammonia equaling less than 0.01% by volume of hydrogen flowing through a chamber before flowing trimethylaluminum and triethylboron and then a subsequent amount of ammonia through the chamber.
1. A device comprising:
a substrate of silicon, wherein the substrate has a Si(111)1×1 surface;
a buffer layer of boron-aluminum nitride overlying the Si(111)1×1 surface of the substrate, wherein the boron-aluminum nitride has a composition of B x Al 1-x N wherein 0.35≦x≦0.45, and wherein the boron-aluminum nitride has a wurtzite-type crystal structure with a cell unit length in a C-plane that is between 64% and 68% of a cell unit length of the silicon on the Si(111)1×1 surface; and
an upper layer of gallium nitride above the buffer layer.
2. The device of claim 1 , wherein the boron-aluminum nitride has the wurtzite-type crystal structure with at least one layer in the C-plane having one atom of boron for each two atoms of aluminum.
3. The device of claim 1 , wherein the silicon and boron-aluminum nitride are oriented as boron-aluminum nitride<0001>∥Si<111>.
4. The device of claim 1 , wherein no amount of metallic aluminum is disposed between the substrate and the buffer layer.
5. The device of claim 1 , further comprising: a second buffer layer comprising aluminum gallium nitride (Al y Ga 1-y N), wherein the second buffer layer of aluminum gallium nitride is disposed between the buffer layer of boron-aluminum nitride and the upper layer of gallium nitride.
6. The device of claim 1 , wherein the buffer layer of boron-aluminum nitride is between 100 and 150 nanometers thick.
7. The device of claim 1 , wherein the substrate is an 8 inch diameter silicon wafer cut along a Si(111) plane, and wherein the entire wafer is formed so that nitrogen atoms of the boron-aluminum nitride form bonds to the Si(111)1×1 surface.