Strong enhancement of photoresponsivity with shrinking the electrodes spacing in few layer GaSe photodetectors

TL;DR

This study demonstrates that reducing electrode spacing in GaSe photodetectors significantly enhances photoresponsivity, achieving a 1700-fold improvement, and provides a theoretical model to explain this phenomenon, advancing high-density 2D optoelectronic integration.

Contribution

The paper reveals that shrinking electrode spacing in GaSe photodetectors boosts responsivity and introduces a theoretical model explaining this effect, enabling high-density 2D optoelectronic integration.

Findings

Photoresponsivity increases as electrode spacing decreases.

Responsivity reaches up to 5,000 AW-1 at optimal conditions.

A theoretical model explains the dependence of responsivity on spacing.

Abstract

A critical challenge for the integration of the optoelectronics is that photodetectors have relatively poor sensitivities at the nanometer scale. It is generally believed that a large electrodes spacing in photodetectors is required to absorb sufficient light to maintain high photoresponsivity and reduce the dark current. However, this will limit the optoelectronic integration density. Through spatially resolved photocurrent investigation, we find that the photocurrent in metal-semiconductor-metal (MSM) photodetectors based on layered GaSe is mainly generated from the photoexcited carriers close to the metal-GaSe interface and the photocurrent active region is always close to the Schottky barrier with higher electrical potential. The photoresponsivity monotonically increases with shrinking the spacing distance before the direct tunneling happen, which was significantly enhanced up to 5,000 AW-1 for the bottom contacted device at bias voltage 8 V and wavelength of 410 nm. It is more than 1,700-fold improvement over the previously reported results. Besides the systematically experimental investigation of the dependence of the photoresponsivity on the spacing distance for both the bottom and top contacted MSM photodetectors, a theoretical model has also been developed to well explain the photoresponsivity for these two types of device configurations. Our findings realize shrinking the spacing distance and improving the performance of 2D semiconductor based MSM photodetectors simultaneously, which could pave the way for future high density integration of 2D semiconductor optoelectronics with high performances.