Ultrahigh-performance heterojunction bipolar phototransistor enabled by bilateral piezoelectric charge modulation effect

Abstract

Heterojunction photodiodes based on p-n junction with enhanced piezo-phototronic effect have been extensively studied. However, the photoresponsivity of conventional photodiodes is small due to the natural zero current gain. Heterojunction phototransistor usually has greater photoresponsivity due to the non-zero current gain. More importantly, heterojunction phototransistor owns two interfaces, offering the opportunity to introduce the bilateral piezoelectric charge modulation effect for further performance enhancement compared to the conventional single-interface piezo-phototronic effect in photodiode. In this work, a base-floating heterojunction bipolar phototransistor (FHPT) based on n-ZnO/p-Si/n-ZnO structure with a spectral detection range from ultraviolet (UV)–visible is demonstrated. The positive piezoelectric charge generated at the two interfaces of the collector junction and the emitter junction, combined with the optimal base width and low resistance base doping concentration of the FHPT, leads to an excellent photoresponsivity (18046 A/W, 365 nm), high detectivity (5.7×1012 Jones), and a wider modulation (7120 %). The physical mechanism leading to the ultrahigh performance is attributed to the cooperative positive piezoelectric charge at the two interfaces, simultaneously reducing the effective base width and lowering the emitter junction barrier. This work illustrates the regulation of heterojunction phototransistor performance by the bilateral piezoelectric charge modulation effect, providing insightful guidance to high-performance phototransistor design.