Gate-tunable Photoresponse Time in BlackPhosphorus-MoS2Heterojunctions

TL;DR

This study investigates how gate voltage influences the photoresponse speed in BP-MoS2 heterojunctions, revealing that the Schottky barrier at the metal interface critically affects carrier transit times and device response times.

Contribution

It demonstrates gate-tunable photoresponse times in BP-MoS2 heterojunctions and elucidates the role of Schottky barriers in controlling photoresponse dynamics.

Findings

Response time of 13 μs in on-state is wavelength-independent.

Off-state Schottky barrier causes wavelength-dependent delay.

Gate control enables tuning of photoresponse speed.

Abstract

We study the rise and decay times in BP-MoS2 heterojunctions through gate- and wavelength-dependent scanning photocurrent measurements. Our results have shown that the Schottky barrier at the MoS2-metal interface plays an important role in the photoresponse dynamics of the heterojunction. When the MoS2 channel is in the on-state, photo-excited carriers can tunnel through the narrow depletion region at the MoS2-metal interface, leading to a short carrier transit time. A response time constant of 13 {\mu}s has been achieved in both the rising and decaying regions regardless of the incident laser wavelength, which is comparable or higher than those of other BP-MoS2 heterojunctions as well as BP and MoS2 based phototransistors. On the other hand, when the MoS2 channel is in the off-state the resulting sizeable Schottky barrier and depletion width make it difficult for photo-excited carriers to overcome the barrier. This significantly delays the carrier transit time and thus the photoresponse speed, leading to a wavelength-dependent response time since the photo-excited carriers induced by short wavelength photons have a higher probability to overcome the Schottky barrier at the MoS2-metal interface than long wavelength photons. These studies not only shed light on the fundamental understanding of photoresponse dynamics in BP-MoS2 heterojunctions, but also open new avenues for engineering the interfaces between two-dimensional (2D) materials and metal contacts to reduce the response time of 2D materials based optoelectronic devices.