Abstract
A High Electron Mobility Transistor (HEMT) includes a first III-V compound layer having a first band gap, and a second III-V compound layer having a second band gap over the first III-V compound layer. The second band gap is greater than the first band gap. A crystalline interfacial layer is overlying and in contact with the second III-V compound layer. A gate dielectric is over the crystalline interfacial layer. A gate electrode is over the gate dielectric. A source region and a drain region are over the second III-V compound layer, and are on opposite sides of the gate electrode.