Tungsten carbide Schottky contact to diamond toward thermally stable photodiode

We use tungsten carbide-based Schottky and ohmic contacts for the fabrication of deep ultraviolet (DUV) photodiodes on boron-doped homoepitaxial diamond layers. The photodiode is isothermally annealed at 500 °C in argon ambient in order to investigate the thermal stability of the electrical and optical properties. The ideality factor is improved to be an ideal value of unity after annealing for 1 h and becomes around 1.5 after subsequent annealing for longer time durations. The leakage current for at least 30 V reverse bias is lower than 10− 14 A before and after annealing for 4 h. The photoresponsivity at 220 nm is enhanced dramatically by a factor of 103 after annealing, resulting in a DUV/visible blind ratio as large as 106 at the reverse bias of 2 V. The work is expected to open a way for developing thermally-stable Schottky contacts to diamond.