Atomistic transport modeling, design principles and empirical rules for Low Noise III-V Digital Alloy Avalanche Photodiodes

TL;DR

This paper models atomistic transport in digital alloy avalanche photodiodes to identify design principles and empirical rules that lead to low noise performance by controlling carrier ionization and transport mechanisms.

Contribution

It introduces an atomistic band inversion model and empirical inequalities to evaluate digital alloys for low noise APDs, advancing design strategies.

Findings

Unipolar avalanche multiplication reduces noise

Carrier transport is suppressed by band structure effects

Proposed inequalities effectively predict low noise suitability

Abstract

A series of III-V ternary and quarternary digital alloy avalanche photodiodes (APDs) have recently been seen to exhibit very low excess noise. Using band inversion of an environment-dependent atomistic tight binding description of short period superlattices, we argue that a combination of increased effective mass, minigaps and band split-off are primarily responsible for the observed superior performance. These properties significantly limit the ionization rate of one carrier type, either holes or electrons, making the avalanche multiplication process unipolar in nature. The unipolar behavior in turn reduces the stochasticity of the multiplication gain. The effects of band folding on carrier transport are studied using the Non-Equilibrium Green's Function Method that accounts for quantum tunneling, and Boltzmann Transport Equation model for scattering. It is shown here that carrier transport by intraband tunneling and optical phonon scattering are reduced in materials with low excess noise. Based on our calculations, we propose five simple inequalities that can be used to approximately evaluate the suitability of digital alloys for designing low noise photodetectors. We evaluate the performance of multiple digital alloys using these criteria and demonstrate their validity.