Tetsu Kachi

An AlSiO/AlN‐interlayer gate stack formed on c ‐plane GaN metal‐oxide‐semiconductor (MOS) devices was previously developed to enhance the interface of the gate insulator. By utilizing this gate stack structure, a channel mobility of over 200 cm 2 Vs −1 on c ‐plane was obtained. However, the threshold voltage was negative because of the polarization charge at the AlN/GaN interface. This study extends the application of this gate stack structure to the nonpolar m ‐plane, which is obtained from a trench sidewall. Both a high channel mobility of 150 cm 2 Vs −1 and a threshold voltage of 1.3 V is successfully achieved, normally‐off operation. This achievement holds significant promise for the gate structure of a GaN trench‐gate MOS field‐effect transistor (MOSFET). The limiting factor of the channel mobility is Coulomb scattering in a low electric field, whereas surface roughness scattering is dominant in a higher field.