A normally-off hydrogen-terminated diamond phototransistor with high responsivity and rejection ratio

Abstract

Phototransistors possess superior detection capabilities, including high responsivity, large light-to-dark current ratio, and flexible gate controllability, making them attractive for diamond-based solar-blind photodetection. This work presents a hydrogen-terminated diamond (H-diamond) phototransistor with a metal-semiconductor field-effect transistor (MESFET) structure. The dark current of the H-diamond phototransistor was suppressed down to an extremely low magnitude of 10⁻¹⁴ A under positive gate voltage (V_GS). Under 222 nm UV illumination, it achieves a remarkable responsivity (R_λ) of 1.42 × 10⁷ A W⁻¹ at negative V_GS. The spectral rejection ratios at positive V_GS reach 5.13 × 10⁸ and 2.11 × 10⁷ for R_222nm/R_365nm and R_222nm/R_275nm, respectively, demonstrating good wavelength selectivity. The persistent photoconductivity (PPC) effect also reveals good charge retention of the phototransistor. These findings establish a novel pathway for diamond device engineering in solar-blind ultraviolet detection through optimized MESFET configuration design.