# Wide‐/Narrow‐Bandgap Heterojunction for High Performance Differential Photodetector with Tunable Response

## TL;DR

A new tunable photodetector is developed using a semiconductor heterojunction, offering high performance and potential for advanced photonic applications.

## Contribution

A novel differential photodetector with tunable modes and high detectivity is introduced using a wide/narrow-bandgap heterojunction.

## Key findings

- The device operates in two tunable modes by adjusting bias voltages.
- It achieves high detectivity (4.5×10¹¹ Jones) and a bandwidth of ≈1 MHz under 1550 nm laser.
- Applications in event-based imaging and encrypted communication are successfully demonstrated.

## Abstract

Amid the rapid advancement in modern photonics and artificial intelligence, optoelectronic devices with enhanced functionalities and high performance hold great promise for complex photonic integrated circuits. Herein, a novel tunable differential photodetector (DPD) is developed based on a wide‐/narrow‐bandgap semiconductor heterojunction, featuring a large conduction band offset at the heterojunction interface. Benefiting from the unique band alignment at the heterojunction interface, this device exhibits interesting characteristics:1) It offers two tunable operational modes, freely switchable between “differential mode” and “normal mode” only by adjusting the bias voltages; 2) While operating in “differential mode” under zero bias, the DPD exhibits high detectivity (4.5×1011 Jones) and broad bandwidth of ≈1 MHz under 1550 nm laser at room temperature; 3) Due to the narrow bandgap of PbSe, the device operates at longer wavelengths than reported to date. An equivalent circuit model is proposed to elucidate the working mechanism that is experimentally observed. The practical applications of the DPD in the event‐based imaging of a moving flame and encrypted communication are further demonstrated. The work establishes a novel approach for optoelectronic devices toward multifunctional integrated photonics applications.

A differential photodetector is developed by applying the unique characteristics of a wide‐/narrow‐bandgap semiconductor heterojunction. The mechanism based on band alignment enables high detectivity and high bandwidth with tunable photoresponse. Applications of the DPD are demonstrated in the event‐based imaging of a moving flame and encrypted communication, showing great potential for multifunctional integrated photonics development.