Patent ID: 8921890

Claim:
A substrate structure comprising: a non-GaN-based substrate; a buffer layer on the non-GaN-based substrate; a GaN-based first material layer on the buffer layer, the GaN-based first material layer being doped with a first impurity that is a first conductive type; a GaN-based second material layer on the GaN-based first material layer, the GaN-based second material layer being doped with a second impurity that is a second conductive type, the GaN-based second material layer having a density of the second impurity that is less than a density of the first impurity in the first GaN-based material layer; and a GaN-based third material layer on the GaN-based second material layer, the GaN-based third material layer being doped with a third impurity that is the first conductive type, the GaN-based third material layer having a density of third impurity that is less than the density of the first impurity of the GaN-based first material layer.