# Wafer‐Scale Bandgap‐Tunable MoS2/PbS Phototransistors Enabled by Solution Processing

## TL;DR

This paper introduces a new method to create large-scale, tunable phototransistors using MoS2/PbS heterostructures with improved performance and high yield.

## Contribution

The paper introduces lateral heterojunctions and plasma-enhanced solution processing for wafer-scale, bandgap-tunable MoS2/PbS phototransistors.

## Key findings

- Lateral heterojunctions enable bandgap tunability from 1.24 to 0.61 eV via Type-II band alignment.
- Plasma treatment improves wafer-scale fabrication with 97% yield and high device performance.
- Devices show 88 A/W responsivity, 4.77 × 10^12 Jones detectivity, and 3.16 × 10^7 on/off ratio.

## Abstract

Molybdenum disulfide (MoS2)/lead sulfide (PbS) heterostructures exhibit exceptional potential because of their strong light‐matter interactions and high carrier mobility. Critically, bandgap engineering can further optimize the light‐absorption range for next‐generation phototransistors. However, the bandgap engineering capability for MoS2/PbS heterojunctions formed by conventional transfer‐after‐chemical vapor deposition (CVD) fabrication is typically inherently restricted due to solely vertical interlayer coupling. Here, to realize wafer‐scale bandgap‐tunable MoS2/PbS phototransistors, we investigate the band structure of vertical and lateral MoS2/PbS heterojunctions via ab initio calculations and find that lateral heterojunctions in heterostructures dominate the bandgap tunability via tuning of the Type‐II band alignment. To achieve wafer‐scale uniformity, we investigated how plasma treatment modulates the thin‐film surface energy, and the results substantially improved fabrication scaling of MoS2/PbS heterojunctions from traditional micro‐scale level to an incredible 4‐inch wafer‐scale with near‐ideal yields (97%) and enabled bandgap tunability (from 1.24 to 0.61 eV). The resulting phototransistors exhibit a maximum responsivity of 88 A/W, specific detectivity of 4.77  ×  1012 Jones, and a typical on/off ratio of 3.16  ×  107. This work establishes a pathway for developing wafer‐scale bandgap‐tunable optoelectronics.

This work advances bandgap‐tunable MoS2/PbS phototransistors by introducing lateral heterojunctions, which enable superior tunable bandgap (1.24–0.61 eV) via Type‐II alignment. Plasma‐enhanced solution processing ensures uniform 4‐inch wafer‐scale fabrication with 97% yield. The optimized devices achieve high responsivity (88 A/W), detectivity (4.77 × 101
2 Jones), and on/off ratio (3.16 × 107), providing a pathway for scalable, tunable optoelectronics.