Realizing high zero-bias gain in a GaN-based bipolar phototransistor through thin-base configuration for ultraviolet imaging

Abstract

Ultraviolet (UV) detectors with high gain at low bias are urgently demanded. In this study, a GaN-based UV bipolar phototransistor (BPT) with high zero-bias gain was obtained based on a n–p–i–n homo-structure. A thin-base structure is proposed to suppress excess hole recombination and, thus, to increase optical gain. The BPT with a 50 nm base showed zero-bias near-saturation photocurrent under UV illumination. The zero-bias photocurrent and detectivity increased with an increasing light power density of 52.6 A W⁻¹ and 5.7 × 10¹² Jones at 360 nm under an incident light power density (P_in) of 121 μW cm⁻², corresponding to a gain of ∼180. Numerical simulations and BPTs with thick bases were employed to investigate the gain mechanism and response characteristics of the as-prepared BPT. A UV image was obtained using the thin-base GaN-based BPT and a scanning imaging method at zero bias, and the zero-bias sampling frequency was found to be ≥100 kHz. The GaN-based thin-base BPT design offers an effective and convenient strategy to achieve zero-bias high-gain UV detection for applications such as UV imaging.