Systematic study of high performance GeSn photodiodes with thick absorber for SWIR and extended SWIR detection

TL;DR

This paper systematically investigates high-performance GeSn photodiodes with thick absorbers for SWIR detection, revealing their physical properties, performance limits, and optimization strategies for improved device design.

Contribution

It provides the first comprehensive empirical analysis of thick GeSn photodiodes, detailing their performance, physics, and optimization pathways for SWIR applications.

Findings

High responsivity up to 0.59 A/W at 1.55 μm

Low dark current density down to 2 x 10^-2 A/cm^2

Detection cutoff wavelengths up to 2.5 μm at 8% Sn

Abstract

Germanium-tin (GeSn) photodiodes potentiate a viable solution to integrate SWIR and extended SWIR detection technology into CMOS processing line. However, challenges in the growth of thick, high quality GeSn limit the device absorber thickness, making it impossible to ascertain the performance limit of GeSn photodiodes. An in-depth understanding of their device physics and a clear optimization pathway towards commercial-grade devices remain elusive. This work presents a systematic empirical study of GeSn photodiodes with thick absorber (2 to 8% Sn content, up to 2630 nm thick), showing high responsivity up to 0.59 A.W-1 at 1.55 {\mu}m and 0.43 A.W-1 at 2 {\mu}m wavelengths, low dark current density down to 2 x 10-2 A.cm-2, and high detection cutoff wavelengths up to 2.1 and 2.5 {\mu}m at 5% and 8% Sn, respectively. Using specific doping design (P-i-N and N-i-P), an in-depth analysis is presented on the impact of junction position, p-type background carrier concentration, bulk/ surface defects and photocarrier diffusion length - on photodetection performance. Different optimization strategies for GeSn photodiodes, in particular at high Sn content, are proposed.