Gallium nitride-based semiconductor stacked structure, method for fabrication thereof, gallium nitride-based semiconductor device and lamp using the device
A gallium nitride-based semiconductor stacked structure includes a single crystal substrate, a low-temperature buffer layer grown at a low temperature in a region contiguous to the single crystal substrate and a gallium nitride-based semiconductor layer overlying the low-temperature buffer layer. The low-temperature buffer layer possesses therein a single crystal layer formed of a hexagonal Al X Ga γ N-based Group III nitride material containing gallium predominantly over aluminum, wherein 0.5<γ≦1 and X+γ=1. The single crystal layer has crystal defects at a smaller density on a (10-10) crystal face than on a (11-20) crystal face. A method for production of the gallium nitride-based semiconductor stacked structure is also disclosed.
1. A gallium nitride-based semiconductor stacked structure comprising:
a single crystal substrate;
a low-temperature buffer layer grown at a low temperature in a region contiguous to the single crystal substrate; and
a gallium nitride-based semiconductor layer overlying the low-temperature buffer layer;
wherein the low-temperature buffer layer possesses therein a single crystal layer formed of a hexagonal Al X Ga γ N-based Group III nitride material containing gallium predominantly over aluminum, in which 0.5<γ≦1, X+γ=1, and the single crystal layer has crystal defects at a smaller density on a (10-10) crystal face than on a (11-20) crystal face.
2. A gallium nitride-based semiconductor stacked structure according to claim 1 , wherein the single crystal substrate is a sapphire (α-alumina single crystal) substrate having a {0001} face (C plane) surface thereof.
3. A gallium nitride-based semiconductor stacked structure according to claim 1 , wherein the single crystal substrate is a silicon carbide substrate having a {0001} face (C plane) surface thereof.
4. A gallium nitride-based semiconductor stacked structure according to claim 1 , wherein the gallium nitride-based semiconductor layer has a [10-10] direction thereof laid in parallel to a [10-10] direction of the single crystal layer of the low-temperature buffer layer.
5. A gallium nitride-based semiconductor stacked structure according to claim 1 , wherein the single crystal layer of the low-temperature buffer layer has crystal defects on a (10-10) crystal face at a density of ⅕ or less of a density of crystal defects on a (11-20) crystal face.
6. A method for the production of a gallium nitride-based semiconductor stacked structure, comprising the steps of:
forming on a single crystal substrate a low-temperature buffer layer grown at a low temperature falling in a range of 250° C. to 500° C.;
forming a gallium nitride-based semiconductor layer on the low-temperature buffer layer; and
forming in the low-temperature buffer layer a single crystal layer made of a hexagonal Al X Ga γ N-based Group III nitride material containing gallium predominantly over aluminum, in which 0.5<γ≦1, X+γ=1, by causing gallium raw material to reach a surface of the substrate before aluminum raw material;
wherein the single crystal layer has crystal defects on a (10-10) crystal face at a lower density than on a (11-20) crystal face.
7. A method according to claim 6 , wherein the single crystal substrate is a sapphire (α-alumina single crystal) substrate having a {0001} face (C plane) surface thereof.
8. A method according to claim 6 , wherein the single crystal substrate is a silicon carbide substrate having a {0001} face (C plane) surface thereof.
9. A method according to claim 6 , wherein the growth rate of the low-temperature buffer layer is grown at a growth rate in a range of 1 to 3 nm/min.
10. A gallium nitride-based semiconductor device using the gallium nitride-based semiconductor stacked structure according to claim 1 .
11. A lamp using the gallium nitride-based semiconductor device according to claim 10 .