Promoted Potential of Heterojunction Phototransistor for Low-Power Photodetection by Surface Sulfur Treatment

Temperature-dependent dark and optical characteristics of the heterojunction phototransistors (HPTs) with and without sulfur treatment are studied. As compared to the HPT without treatment (HPT A), treatment at for leads to a reduced p-i-n dark current and a reduced collector dark current for the HPT (HPT D) in the emitter-floated and base-floated configurations, respectively. Moreover, the effective reduction of the surface defects also induces an enhanced p-i-n photocurrent . The enhanced combined with the promoted dc current gain results in an enhanced optical gain and signal-to-noise ratio (SNR). For HPT A (D) under at , the is 1.42 (20.3) while the SNR is 42 (94) dB. Experimental results indicate that the treated HPTs, compared to the untreated one, are more sensitive to low-power illumination.