# A Study of the Avalanche Multiplication and Excess Noise in Al x In1–x AsγSb1‑ γ Avalanche Photodiodes Lattice-Matched to GaSb

## TL;DR

This paper studies a new type of photodiode that can detect light at long wavelengths with high sensitivity while managing noise.

## Contribution

The paper presents a systematic study of AlInAsSb avalanche photodiodes with SACM structure for improved performance at long wavelengths.

## Key findings

- The SACM APD achieved 64% and 10% quantum efficiency at 1.55 μm and 2 μm wavelengths.
- The device demonstrated a maximum avalanche gain of 197 with an excess noise of 3.1 at a gain of 10.
- The APD is suitable for photon-starved applications like gas sensing and LiDAR.

## Abstract

High-sensitivity linear-mode avalanche photodiodes (APDs)
that
operate beyond 1.65 μm and up to 2 μm require a narrow
bandgap that also gives rise to high dark currents, especially when
subject to the large electric fields necessary for avalanche multiplication.
This has led to increasing interest in separate absorption, charge,
and multiplication (SACM) detectors where the narrow bandgap absorber
has a low electric field and the wider bandgap multiplication region
provides the gain. A systematic study of Al0.7In0.3As0.31Sb0.69 grown lattice-matched on GaSb
as the multiplication layer has been undertaken on p–i–n
structures varying in width from 0.1 to 1.5 μm and the ionization
coefficients and excess noise extracted over a wide electric field
range (195 kV/cm–830 kV/cm). When integrated with a lattice-matched
Al0.3In0.7As0.64Sb0.36 absorption layer, such an SACM APD is found to demonstrate a quantum
efficiency of 64% and 10% for the wavelengths of 1.55 and 2 μm,
respectively, at punch-through, without any antireflection coating.
The device shows a maximum avalanche gain of 197 with an excess noise
of 3.1 at a gain of 10. Such APDs can be potentially used in a receiver
for many photon-starved applications, including gas sensing and LiDAR.