Thermally stable solar-blind diamond UV photodetector

Thermally stable, deep-ultraviolet (DUV) photodetectors are developed by fabricating a semi-transparent tungsten carbide (WC) or hafnium nitride (HfN) Schottky contact and an annealed Ti/WC Ohmic contact on a boron-doped homoepitaxial p-type diamond layer. Thermal annealing at 500 °C improves the rectifying current–voltage characteristics of the photodiode, resulting in a dramatic enhancement (by a factor of 10³) of DUV responsivity at 220 nm. The discrimination ratio between DUV and visible light is measured to be as large as 10⁶ at a reverse bias voltage as small as 2 V, and it remains almost constant after annealing at 500 °C for 5 h. The short-circuit photocurrent of the HfN Schottky photodiode gradually decreases as the annealing temperature increases, which is well explained by the dependence of the depletion layer width beneath the contact interface on the annealing temperature. In contrast, the short-circuit photocurrent of the WC photodiode is rapidly reduced as the temperature increases. The B doping is found to affect the time response property and reducing the B concentration significantly reduces the response time. Metal carbide and nitride contacts for diamond are thus useful for developing a thermally stable diamond UV photodetector.