# Observation of ballistic avalanche phenomena in nanoscale vertical InSe/BP heterostructures

## TL;DR

This paper reports the discovery of ballistic avalanche phenomena in nanoscale InSe/BP heterostructures, enabling ultra-sensitive mid-IR detection and steep subthreshold swings with low noise, due to impact ionization without scattering.

## Contribution

It demonstrates the first observation of ballistic avalanche in sub-MFP scaled heterostructures, advancing nanoscale impact ionization device technology.

## Key findings

- Low avalanche threshold (<1V) achieved
- Ballistic impact ionization confirmed by transport measurements
- Devices exhibit ultra-steep subthreshold swing and low noise

## Abstract

Initiating impact ionization of avalanche breakdown essentially requires applying a high electric field in a long active region, hampering carrier-multiplication with high gain, low bias and superior noise performance. Here we report the observation of ballistic avalanche phenomena in sub-MFP scaled vertical indium selenide (InSe)/black phosphorus (BP) heterostructures. The heterojunction is engineered to avalanche photodetectors (APD) and impact ionization transistors, demonstrating ultra-sensitive mid-IR light detection (4 {\mu}m wavelength) and ultra-steep subthreshold swing, respectively. These devices show an extremely low avalanche threshold (<1 volt), excellent low noise figures and distinctive density spectral shape. Further transport measurement evidences the breakdown originals from a ballistic avalanche phenomenon, where the sub-MFP BP channel enables both electrons and holes to impact-ionize the lattice and abruptly amplify the current without scattering from the obstacles in a deterministic nature. Our results shed light on the development of advanced photodetectors and efficiently facilitating carriers on the nanoscale.

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Source: https://tomesphere.com/paper/1901.10392