Systematic study on photoexcited carrier dynamics related to defects in GeSn films with low Sn content at room temperature

Abstract

Germanium-tin (GeSn) alloys have received much attention thanks to their optical/electrical properties and their operation in the mid-infrared range. However, dislocations/defects in GeSn films serve as trap states, limiting radiative recombination/generation via band-edges. In this work, the impact of the trap states in GeSn with varying Sn contents is investigated. The systematic study reveals that the defects/dislocations in GeSn contribute to the carrier dynamics, mainly originated from the trap states near GeSn/Ge interface. Through photoluminescence (PL) study, the broad PL peak of the trap state for GeSn exists at similar to 0.57 eV. The increase in Sn content mitigates the trap-related carrier dynamics. Besides, the increase in GeSn thickness effectively suppresses the interface-related carrier dynamic. By increasing thickness from 180 to similar to 900 nm, the external quantum efficiency is enhanced by similar to 10x. This study provides a comprehensive understanding of trap-related carrier dynamics in a GeSn material system at room temperature.