Normally-off operation in vertical diamond MOSFETs using an oxidized Si-terminated diamond channel

Abstract

We fabricated (001) vertical diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with oxidized Si-terminated (C–Si–O) diamond channels on the surfaces and trench sidewalls. The C–Si–O diamond surface is approximately 1.0 eV weaker in negative electron affinity than the hydrogen-terminated (C–H) diamond surface, resulting in a smaller valence band bending between the interface of C–Si–O diamond surface and Al2O3, and larger the difference between the energy values of the fermi level and the valence band on the top (EF−EV), and the threshold voltage (Vth) shifts in the negative direction. As a result, the maximum drain current density was 108 mA/mm, the Vth was −9.0 V. Compared with conventional vertical diamond FETs using a C–H channel, the Vth was shifted more than 20 V in the negative direction to reach normally-off mode. The normally-off operation was achieved while maintaining high current density, which is the first case of normally-off operation that has been observed in vertical diamond FETs. In, addition, it was confirmed that the diode functions as a freewheeling diode by adding a reverse drain voltage and allowing current to flow, and the change of current-voltage characteristics was also investigated by swapping the source and drain positions and performing measurements.