# Triggering avalanche-like ultraviolet photomultiplication phenomena in ultrathin amorphous/crystalline gallium nitride heterostructures

## TL;DR

Researchers created a new type of photodetector that achieves high light sensitivity with very low background noise using a unique amorphous/crystalline material interface.

## Contribution

A novel amorphous/crystalline interface design enables trap-assisted carrier multiplication without impact ionization, reducing dark current.

## Key findings

- The a-GaON/GaN heterostructure achieved a gain of 3.9 × 10⁶ and responsivity of 4.3 × 10⁷ A/W at 35 V.
- Dark current was as low as ~0.7 pA, outperforming state-of-the-art UV avalanche photodiodes.
- The device was integrated into proof-of-concept UV hardware systems for optoelectronic applications.

## Abstract

Avalanche phenomena, triggered by carrier multiplication through impact ionization under high electric fields, form the operating principle of avalanche photodiodes. However, this process inevitably leads to amplified dark current, thereby limiting the photo-to-dark-current ratio despite large gain. Here, we demonstrate avalanche-like nonlinear photocurrent amplification while we maintain ultralow dark current in an amorphous-gallium oxynitride (a-GaON)/gallium nitride (GaN) heterostructure formed via a two-step “amorphization-recrystallization” process. Instead of relying on the impact ionization process, the engineered amorphous/crystalline interface enables trap-assisted photo-induced carrier multiplication behavior at low voltages, yielding a large gain (3.9 × 106) and ultrahigh responsivity (4.3 × 107 amperes per watt) at 35 volts, with an ultralow dark current (~0.7 picoamperes), which are strongly competitive relative to state-of-the-art ultraviolet avalanche photodiodes. We further present proof-of-concept ultraviolet hardware systems incorporated with the newly constructed device. This amorphous/crystalline interfacial engineering strategy presents an unexploited, simple, and scalable device paradigm for fabricating advanced photodetectors in next-generation compact and integrated optoelectronic systems.

Giant photomultiplication with ultralow dark current achieved in amorphous-GaON/GaN heterostructures.