Buffer layer for Gallium Nitride-on-Silicon epitaxy

1 . A method for forming a multi-layer AlN buffer structure on silicon, the method comprising:

providing a (111) oriented silicon substrate having a top surface;

using atomic layer deposition to deposit, at a predetermined temperature range, a first layer of AlN on the top surface;

using first and second precursor materials, characterized by a first V-III ratio, to deposit, at the predetermined temperature range, a plurality of AlN islands forming a second layer overlying and in contact with the first layer;

using the first and second precursor materials, characterized by a second V-III ratio, to deposit, at the predetermined temperature range, a third layer of AlN, the third layer overlying and in contact with the islands and the first layer between the islands, forming domains; and

using the first and second precursor materials, characterized by a third V-III ratio, to deposit, at the predetermined temperature range, a fourth layer of AlN, the fourth layer overlying and in contact with the third layer, wherein the fourth layer is characterized by a fourth layer top surface that is anatomically smooth.

2 . The method of claim 1 , wherein the substrate has an offcut angle between −1 degree and +1 degree.

3 . The method of claim 1 , wherein the predetermined temperature range is between 1000° C. and 1200° C.

4 . The method of claim 1 , wherein the first layer has a thickness between 0.3 nm and 10 nm.

5 . The method of claim 1 , wherein the first V-III ratio is between 700 and 1000.

6 . The method of claim 1 , wherein the second V-III ratio is between 300 and 700.

7 . The method of claim 1 , wherein the third V-III ratio is between 10 and 200.

8 . The method of claim 1 , wherein the third layer contains multiple crystalline domains.

9 . The method of claim 1 , wherein the fourth layer has a surface morphology showing layer growth.

10 . A method of forming a multi-layer buffer structure on silicon, the method comprising:

providing a (111) oriented silicon substrate having a top surface;

forming on the top surface, at a first temperature range, a first multilayer buffer structure comprising AlN films;

forming on top of the first multilayer buffer structure, at a second temperature range, a second multilayer buffer structure comprising AlGaN films; and

growing, at a third temperature range, a first epitaxial GaN layer directly overlying and in contact with the second multilayer buffer structure;

wherein forming the first multilayer buffer structure comprises:

using atomic layer deposition to deposit a first layer of AlN overlying and in direct contact with the top surface;

using first and second precursor materials, characterized by a first V-III ratio, to deposit a plurality of AlN islands forming a second layer overlying and in contact with the first layer;

using the first and second precursor materials, characterized by a second V-III ratio, to deposit a third layer of AlN, the third layer overlying and in contact with the islands and the first layer between the islands, forming domains; and

using the first and second precursor materials, characterized by a third V-III ratio, to deposit a fourth layer of AlN, the fourth layer overlying and in contact with the third layer, wherein the fourth layer is characterized by a fourth layer top surface that is anatomically smooth;

wherein forming the second multilayer buffer structure comprises:

forming an Al x Ga 1-x N layer directly overlying and in direct contact with the fourth layer of AlN, where 0<x=<0.9; and

forming an Al y Ga 1-y N layer directly overlying and in contact with the Al x Ga 1-x N layer, where y<=x.

11 . The method of claim 10 , wherein the substrate has an off-cut angle between −1 degree and +1 degree.

12 . The method of claim 10 , wherein the first temperature range is between 1000° C. and 1200° C.

13 . The method of claim 10 , wherein the first layer has a thickness between 0.3 nm and 10 nm.

14 . The method of claim 10 , wherein the first V-III ratio is between 700 and 1000, the second V-III ratio is between 300 and 700, and the third V-III ratio is between 10 and 200.

15 . The method of claim 10 , wherein the third layer contains multiple crystalline domains.

16 . The method of claim 10 , wherein the third layer of AlN has a surface morphology showing layer growth.

17 . The method of claim 10 , wherein the second temperature range is between 800° C. and 1100° C.

18 . The method of claim 10 , wherein the second temperature range is between 900° C. and 1200° C.

19 . A multi-layer buffer structure for high quality GaN on a (111) silicon substrate, the structure comprising:

a first AlN layer overlying and in direct contact with the silicon substrate;

a second AlN layer overlying and in direct contact with the first AlN layer;

a third AlN layer overlying and in direct contact with the second AlN layer;

a fourth AlN layer overlying and in direct contact with the third AlN layer; and

a first AlGaN layer overlying and in direct contact with the fourth AlN layer, the first AlGaN layer having a top surface suited for the growth thereupon of high quality GaN;

wherein the second AlN layer comprises multiple crystal domains formed by island growth over the first AlN layer.

20 . The multi-layer buffer structure of claim 19 , further comprising:

a second AlGaN layer overlying and in direct contact with the first AlGaN layer; the second AlGaN layer having a top surface suited for the growth thereupon of high quality GaN.