Gallium nitride epitaxial structures for power devices
A method for making a multilayered device on an engineered substrate having a substrate coefficient of thermal expansion includes growing a buffer layer on the engineered substrate, and growing a first epitaxial layer on the buffer layer. The first epitaxial layer is characterized by an epitaxial coefficient of thermal expansion substantially equal to the substrate coefficient of thermal expansion.
1. An epitaxial semiconductor structure comprising:
an engineered substrate having a substrate coefficient of thermal expansion, the engineered substrate comprising:
a polycrystalline ceramic core;
a barrier layer encapsulating the polycrystalline ceramic core;
a bonding layer coupled to the barrier layer; and
a single crystalline silicon layer coupled to the bonding layer;
a buffer layer coupled to the single crystalline silicon layer;
a silicon nitride partial layer coupled to the buffer layer; and
an epitaxial layer formed on the silicon nitride partial layer, wherein the epitaxial layer is characterized by an epitaxial coefficient of thermal expansion substantially equal to the substrate coefficient of thermal expansion.
2. The epitaxial semiconductor structure of claim 1 wherein the silicon nitride partial layer comprises a partial monolayer of silicon nitride.
3. The epitaxial semiconductor structure of claim 1 wherein the epitaxial layer comprises gallium nitride (GaN).
4. The epitaxial semiconductor structure of claim 3 further comprising one or more doped GaN layers coupled to the epitaxial layer.
5. The epitaxial semiconductor structure of claim 4 wherein a doping density for one or more of the one or more doped GaN layers ranges from 1×10 15 to 5×10 19 cm −3 .
6. The epitaxial semiconductor structure of claim 4 wherein a doping density for the one or more doped GaN layers is associated with intentional doping.
7. The epitaxial semiconductor structure of claim 4 wherein the one or more doped GaN layers comprise an n-type GaN layer.
8. The epitaxial semiconductor structure of claim 7 wherein the n-type GaN layer comprises silicon.
9. The epitaxial semiconductor structure of claim 4 wherein the one or more doped GaN layers comprise a p-type GaN layer.
10. The epitaxial semiconductor structure of claim 9 wherein the p-type GaN layer comprises magnesium.
11. The epitaxial semiconductor structure of claim 4 further comprising at least one undoped GaN layer coupled to the epitaxial layer.
12. The epitaxial semiconductor structure of claim 11 wherein a dopant density of the at least one undoped GaN layer is on the order of 1×10 16 cm −3 .
13. The epitaxial semiconductor structure of claim 11 wherein a dopant density of the at least one undoped GaN layer is less than 1×10 16 cm −3 .
14. The epitaxial semiconductor structure of claim 3 further comprising an additional silicon nitride partial layer coupled to the epitaxial layer.
15. The epitaxial semiconductor structure of claim 3 wherein the silicon nitride partial layer comprises multiple silicon nitride partial monolayers.
16. An epitaxial semiconductor structure comprising:
an engineered substrate characterized by a substrate coefficient of thermal expansion and comprising:
a polycrystalline ceramic core;
a barrier layer encapsulating the polycrystalline ceramic core;
a bonding layer coupled to the barrier layer; and
a single crystalline silicon layer coupled to the bonding layer;
a buffer layer coupled to the single crystalline silicon layer;
a silicon nitride partial layer coupled to the buffer layer; and
a gallium nitride (GaN) epitaxial layer formed on the silicon nitride partial layer, wherein the GaN epitaxial layer is characterized by an epitaxial coefficient of thermal expansion substantially equal to the substrate coefficient of thermal expansion.
17. The epitaxial semiconductor structure of claim 16 further comprising one or more doped GaN layers coupled to the GaN epitaxial layer, wherein the one or more doped GaN layers are characterized by a doping density greater than 1×10 16 cm −3 .
18. The epitaxial semiconductor structure of claim 17 wherein each of the one or more doped GaN layers forms one of a set of epitaxial layers comprising:
a doped GaN layer characterized by a doping density greater than 1×10 16 cm −3 ; and
an undoped GaN layer coupled to the doped GaN layer, wherein the undoped GaN layer is characterized by a dopant density less than 1×10 16 cm −3 .
19. The epitaxial semiconductor structure of claim 17 wherein the one or more doped GaN layers comprise an n-type GaN layer and a p-type GaN layer.
20. The epitaxial semiconductor structure of claim 19 further comprising an undoped GaN layer disposed between the n-type GaN layer and the p-type GaN layer, wherein the undoped GaN layer is characterized by a dopant density on the order of 1×10 16 cm −3 .
21. The epitaxial semiconductor structure of claim 16 wherein the silicon nitride partial layer comprises a partial monolayer of silicon nitride.
22. The epitaxial semiconductor structure of claim 16 further comprising an additional silicon nitride partial layer coupled to the GaN epitaxial layer.