Patent ID: 11869942
Assignee: SILTRONIC AG
Field: Semiconductors (Electrical engineering)
Classification: CPC H | IPC H

Claim 9:
10. A method for producing a heteroepitaxial wafer of claim 1, the method comprising the following steps in the order given:
a) providing a silicon substrate having a diameter and a thickness, and depositing a multiplicity of layers on the silicon substrate, thereby forming a layered substrate, wherein depositing comprises:
b) depositing an AlN nucleation layer on the silicon substrate;
c) depositing on the AlN nucleation layer a first strain building layer which is an AlzGa1-zN layer having a first average Al content z, wherein 0<z;
d) depositing on the first strain building layer a first strain preserving block comprising not less than 5 and not more than 50 units of a first sequence of layers wherein the layers of the first sequence of layers have an Al content which decreases within the units with increasing distance from the silicon substrate, the first sequence layers of each unit comprising d1) an AlN layer and d2) at least two AlGaN layers differing with respect to their Al content, one AlGaN layer of the first sequence of layers being a continuously graded composition AlGaN layer, the first strain preserving block having a second average Al content y, wherein y>z;
e) depositing on the first strain preserving block a second strain building layer which is an AlxGa1-xN layer having a third average Al content x, wherein 0<x<y;
f) depositing on the second strain building layer a second strain preserving block comprising not less than 5 and not more than 50 units of a second sequence of layers, the second sequence of layers of each unit comprising an AlN layer and at least one AlGaN layer, the second strain preserving block having a fourth average Al content w, wherein x<w<y; and
g) optionally depositing a third strain building layer which is an AlvGa1-vN layer having a fifth average Al content v, wherein 0<v<w, and
h) optionally depositing a superlattice block containing AlN and AlGaN layers, the superlattice block having a sixth average Al content u, where u>v and u<w;
depositing a GaN layer on the second strain preserving block, or on the third strain building layer when present, or on the superlattice block when present.