Application of Sputtering-Deposited AlN Films to Gate Dielectric for AlGaN/GaN Metal--Insulator--Semiconductor Heterojunction Field-Effect Transistor

AlN films deposited by RF magnetron sputtering are applied to AlGaN/GaN metal--insulator--semiconductor heterostructure field-effect transistors (MIS-HFETs) as a gate dielectric. X-ray photoelectron spectroscopy (XPS) was used to characterize the AlN films, showing their chemical bonds and the bandgap by N 1s electron energy loss spectroscopy. The AlGaN/GaN MIS-HFET with a gate length of 150 nm was successfully fabricated, exhibiting low gate leakage currents for both reverse and forward biases, which are at least four orders of magnitude lower than those of reference Schottky-HFETs. Although these results support the possibility of sputtering-deposited AlN as a gate insulator, there are AlN/AlGaN interface states unfavorable for device performance, which were investigated by the frequency dispersion in the capacitance--voltage ($C$--$V$) characteristics.