Non-Layered Te/In2S3 Tunneling Heterojunctions with Ultrahigh Photoresponsivity and Fast Photoresponse

A photodetector based on 2D non-layered materials can easily utilize the photogating effect to achieve considerable photogain, but at the cost of response speed. Here, a rationally designed tunneling heterojunction fabricated by vertical stacking of non-layered In2S3 and Te flakes is studied systematically. The Te/In2S3 heterojunctions possess type-II band alignment and can transfer to type-I or type-III depending on the electric field applied, allowing for tunable tunneling of the photoinduced carriers. The Te/In2S3 tunneling heterojunction exhibits a reverse rectification ratio exceeding 10(4), an ultralow forward current of 10(-12) A, and a current on/off ratio over 10(5). A photodetector based on the heterojunctions shows an ultrahigh photoresponsivity of 146 A W-1 in the visible range. Furthermore, the devices exhibit a response time of 5 ms, which is two and four orders of magnitude faster than that of its constituent In2S3 and Te. The simultaneously improved photocurrent and response speed are attributed to the direct tunneling of the photoinduced carriers, as well as a combined mechanism of photoconductive and photogating effects. In addition, the photodetector exhibits a clear photovoltaic effect, which can work in a self-powered mode.