Vertical-type Schottky-barrier photodiode using p-diamond epilayer grown on heavily boron-doped p+-diamond substrate

We investigate electrical and optical properties of a vertical-type Schottky-barrier photodiode (SPD) using a boron (B)-doped p-diamond epilayer grown on a heavily B-doped p+-diamond (100) substrate with B concentration ([B]) of 1 × 1020 cm− 3 by microwave plasma chemical-vapor deposition. Surface morphology and [B] in the epilayer are strongly affected by the growth temperature (Tg). Smooth surface and low [B] of (3 ± 2) × 1015 cm− 3 with an abrupt [B] profile at epilayer interface are reproducibly obtained for Tg lower than 900 °C. The vertical-type SPD with a semitransparent WC Schottky contact is fabricated on an oxidized surface of the p-diamond epilayer. The SPDs with an ideality factor lower than 1.1 and a reverse leakage current less than 10− 14 A are reproducibly obtained. The SPD is operable at zero or reverse bias mode with a fast response speed less than 1 s. The external quantum efficiency for 220-nm light illumination is measured to be almost constant value of 3.5 ± 0.5% with increasing the reverse bias voltage from 0 to 5 V before and after annealing at 400 °C for 10 min. It is found that the vertical-type SPD using p+-diamond substrate does not provide the photoconductivity gain property.