The invention discloses a
heterojunction HEMT (
High Electron Mobility
Transistor) device based on an AlN buffer layer on an AlN substrate and a preparation method, and mainly solves the problems of high
dislocation density, large electric leakage, poor heat
conductivity, serious current collapse and low channel two-dimensional
electron gas concentration of the buffer layer of the existing similar device. The device comprises a substrate, a buffer layer, a channel layer, a
barrier layer and a cap layer from bottom to top, a drain
electrode and a source
electrode are arranged on the two sides of the cap layer, a gate
electrode is arranged in the middle of the cap layer, a
passivation layer covers the top of the device, and the substrate is an AlN
single crystal substrate; the buffer layer adopts an AlN thin film with the thickness of 60 nm to 400 nm; the
barrier layer is one or a combination of more of AlGaN, InAlN, AlN, AlScN and
Si doped AlGaN; and the
passivation layer is one or a combination of more of air, SiO2, Al2O3 and SiNx. The high-power
microwave radio frequency device has the advantages of low
on resistance, high reverse
voltage resistance, high output power, small grid electric leakage and higher grid control capability, and can be used as a high-power
microwave radio frequency device.