Role of Layer Thickness and Field-Effect Mobility on Photoresponsivity of Indium Selenide (InSe) Based Phototransistors

TL;DR

This study investigates how layer thickness and field-effect mobility influence the photoresponsivity of InSe-based phototransistors, revealing that thinner layers with higher mobility yield greater responsivity, which can be further enhanced with gate voltage.

Contribution

It provides a detailed correlation between layer thickness, mobility, and photoresponsivity in InSe FETs, highlighting the potential for tuning optoelectronic properties for applications.

Findings

Responsivity increases with higher mobility and thinner layers.

Maximum responsivity of 7.84 A/W at 20 nm thickness.

Responsivity can be enhanced with gate voltage.

Abstract

Understanding and optimizing the properties of photoactive two-dimensional (2D) Van der Waals solids are crucial for developing optoelectronics applications. Here we present a detailed investigation of layer dependent photoconductive behavior of InSe based field-effect transistors (FETs). InSe based FETs with five different channel thickness (t, 20 nm < t < 100 nm) were investigated with a continuous laser source of {\lambda} = 658 nm (1.88 eV) over a wide range of illumination power of 22.8 nW < P < 1.29 {\mu}W. All the devices studied, showed signatures of photogating, however, our investigations suggest that the photoresponsivities are strongly dependent on the thickness of the conductive channel. A correlation between the field-effect mobility ({\mu}FE) values (as a function of channel thickness, t) and photoresponsivity (R) indicates that in general R increases with increasing {\mu}FE (decreasing t) and vice versa. The maximum responsivity of ~ 7.84 A/W and ~ 0.59 A/W was obtained for the device with t = 20 nm and t = 100 nm respectively. These values could substantially increase under the application of a gate voltage. The structure-property correlation-based studies presented here indicate the possibility of tuning the optical properties of InSe based photo-FETs for a variety of applications related to photodetector and/or active layers in solar cells.