# Revealing the Active Role of the Gate Electrode in Weak-Light Detection

## TL;DR

This paper shows that the gate electrode in photodetectors plays a key role in detecting weak light, challenging previous assumptions about where photocarriers come from.

## Contribution

The study reveals that the gate, not the channel, is the main source of photocarriers under weak light in thin-film photodetectors.

## Key findings

- Photocarriers under weak illumination mainly originate from the silicon gate, not the MoS2 channel.
- Negative photocurrent is driven by absorption in the gate and is influenced by illumination intensity and V_DS.
- Replacing MoS2 with Au/Ti confirms the gate-driven mechanism, showing the NPC persists.

## Abstract

The contribution of gate materials to the photoresponse
of thin-film
field-effect photodetectors has long been overlooked, with prior studies
focusing primarily on photoconductive and photogating effects within
the sensing layer. Here, we show that under weak illumination, photocarriers
primarily originate from the silicon gate rather than the MoS2 channel. Absorption spectra confirm that light is mainly
absorbed by the gate, driving a negative photocurrent (NPC). The NPC
magnitude and slope vary with illumination intensity and V
DS, suggesting transport dominated by Si/SiO2 interface traps. NPC persists when MoS2 is replaced with
Au/Ti, reinforcing the gate-driven mechanism. At higher powers, band
bending reverses due to competing photovoltaic and trap-induced potentials.
These results highlight the active role of the gate and offer strategies
for device optimization.