Mobility-enhanced normally off hydrogen-terminated diamond FET with low interface state density using Al₂O₃/Nd gate stack

A mobility-enhanced normally off hydrogen-terminated diamond (H-diamond) field-effect transistor (FET) with low interface state density has been realized using Al₂O₃/Nd gate stack deposited by electron beam evaporator. The threshold voltage is extracted to be −1.48 V, indicating an obvious normally off characteristic. The enhancement mode could be ascribed to the large work function difference between Nd and H-diamond. The subthreshold swing is deduced as low as 86.3 mV/dec, revealing a high working speed in the subthreshold region. More importantly, the mobility (518.5 cm²/V·s) has been enhanced due to the fairly low interface state density (3.19 × 10¹¹ cm⁻²·eV⁻¹). In addition, the device exhibits a relatively low trapped charge density and fixed charge density from the C-V characteristic. This work provides a simple method to realize the normally off device and suggests the great potential of adopting the Al₂O₃/Nd gate stack for achieving high-performance H-diamond FET.