Gain characteristics of bipolar junction phototransistors with customized base width using ferroelectric polarization patterning

Abstract

Recently, ferroelectric polarization coupling has been exploited for non-volatile p- and n-type doping of two-dimensional (2D) materials, which enables the design of 2D functional devices via a local polarization pattern. Here, we took advantage of this tool and study the effect of base width to the gain and photodetection performance of bipolar transistors made of few layer MoS2. We found that the space charge region in the base have typical width ∼150–250 nm, and depends on the applied external bias. Such a characteristic causes the compromise between transistor gain and shunt resistance when changing the base width. For photodetection, this hinders the optimization of responsivity without increasing the dark current. As a result, an optimal device was made at the base width ∼1040 nm, from which a responsivity of 160 A W−1, specific detectivity of ∼1.3 × 1012 and the response time ∼9 μs to 680 nm incident light was obtained. The results from the present study shed light on the further design of 2D functional devices that use lateral pn junctions as the basic building blocks.