Semiconductor structure having sets of iii-v compound layers and method of forming the same

A semiconductor structure, comprising:

• a substrate;
• a graded aluminum gallium nitride (AlGaN) layer over the substrate;
• a first gallium nitride (GaN) layer over the AlGaN substrate, the first GaN layer having P-type doping;
• one or more sets of GaN layers over the first GaN layer, each of the one or more sets of GaN layers comprising a lower GaN layer and an upper GaN layer on the lower GaN layer, the upper GaN layer having the P-type doping, and the lower GaN layer being at least one of undoped, unintentionally doped having N-type doping, or doped having the N-type doping;
• a second GaN layer over the one or more sets of GaN layers, the second GaN layer being either undoped or unintentionally doped having the N-type doping
• an active layer over the second GaN layer;
• a source electrode over the second GaN layer;
• a drain electrode over the second GaN layer;
• and
• a gate electrode between the source electrode and the drain electrode and over the active layer.

A method of forming a semiconductor structure, the method comprising:

• forming a first III-V compound layer having a first-type doping over a substrate;
• forming one or more sets of III-V compound layers over the first III-V compound layer, each of the one or more sets of III-V compound layers comprising a lower III-V compound layer and an upper III-V compound layer over the lower III-V compound layer, the upper III-V compound layer having the first type doping, and the lower III-V compound layer being at least one of undoped, unintentionally doped having a second type doping, or doped having the second type doping;
• forming a second III-V compound layer over the one or more sets of III-V compound layers, the second III-V compound layer being either undoped or unintentionally doped having the second type doping;
• and
• forming an active layer over the second III-V compound layer.