Patent ID: 7786511

Claim:
A semiconductor device comprising: a plurality of heterojunctions, said plurality of heterojunctions including a first nitride semiconductor layer, a second nitride semiconductor layer having a bandgap larger than a bandgap of said first nitride semiconductor layer, a third nitride semiconductor layer having a bandgap smaller than the bandgap of said second nitride semiconductor layer, and a fourth nitride semiconductor layer having a bandgap larger than the bandgap of said third nitride semiconductor layer, said first nitride semiconductor layer being at a lowermost position, said second nitride semiconductor layer being on top of said first nitride semiconductor, said third nitride semiconductor layer being on top of said second nitride semiconductor layer, and said fourth nitride semiconductor layer being on top of said third nitride semiconductor layer at a topmost position, a Schottky electrode that is located at a first portion of each of said plurality of heterojunctions to form a Schottky barrier contact with said plurality of heterojunctions; and an ohmic electrode that is located at a second portion of each of said plurality of heterojunctions to form an ohmic contact with said plurality of heterojunctions, wherein a first recess is located at the first portion, the first recess extending from a top surface of said plurality of heterojunctions to said first nitride semiconductor layer, a second recess is located at the second portion, the second recess extending from the top surface of said plurality of heterojunctions to said first nitride semiconductor layer, said Schottky electrode directly contacts a side wall of the first recess, and said ohmic electrode directly contacts a side wall of the second recess.