Giant superlinear power dependence of photocurrent based on layered Ta$_2$NiS$_5$ photodetector

TL;DR

This paper reports a layered Ta$_2$NiS$_5$ photodetector exhibiting a giant superlinear photocurrent response with a power exponent of 1.5, driven by an intrinsic photoconductive mechanism, enhancing optoelectronic efficiency under high illumination.

Contribution

It demonstrates an intrinsic superlinear photoresponse in layered Ta$_2$NiS$_5$, a phenomenon rarely observed in 2D materials without heterostructures or arrays.

Findings

Photocurrent transitions from sublinear to superlinear with increasing power.

Giant superlinearity with a power exponent of 1.5 observed.

Photodetector shows high sensitivity and fast response.

Abstract

Photodetector based on two-dimensional (2D) materials is an ongoing quest in optoelectronics. These 2D photodetectors are generally efficient at low illuminating power but suffer severe recombination processes at high power, which results in the sublinear power dependence of photoresponse and lower optoelectronic efficiency. The desirable superlinear photocurrent is mostly achieved by sophisticated 2D heterostructures or device arrays, while 2D materials rarely show intrinsic superlinear photoresponse. Here, we report the giant superlinear power dependence of photocurrent based on multi-layer Ta$_2$NiS$_5$. While the fabricated photodetector exhibits good sensitivity ($3.1 mS/W$ per square) and fast photoresponse ($31 \mu$$s$), the bias-, polarization-, and spatial-resolved measurements point to an intrinsic photoconductive mechanism. By increasing the incident power density from $1.5 \mu$W/$\mu$$m^{2}$ to $200 \mu$W/$\mu$$m^{2}$, the photocurrent power dependence varies from sublinear to superlinear. At higher illuminating conditions, a prominent superlinearity is observed with a giant power exponent of $\gamma=1.5$. The unusual photoresponse can be explained by a two-recombination-center model where the distinct density of states of the recombination centers effectively closes all recombination channels. The fabricated photodetector is integrated into camera for taking photos with enhanced contrast due to the superlinearity. Our work provides an effective route to enable higher optoelectronic efficiency at extreme conditions.