Non-Layered Te/In 2 S 3 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 In 2 S 3 and Te flakes is studied systematically. The Te/In 2 S 3 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/In 2 S 3 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 In 2 S 3 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.