Control of the Urbach band tail and interband dephasing time with post-growth annealing in low-temperature-grown GaAs

D Webber,K C Hall,M Dobrowolska,J K Furdyna,X Liu

doi:10.1063/1.5020559

Abstract

Femtosecond four-wave mixing experiments on low-temperature-grown (LT-) GaAs for a range of post-growth annealing temperatures indicate that the Urbach band tail abruptly diminishes above 550°C due to the conversion of As-related point defects to As clusters and that the interband dephasing time is limited by scattering with As point defects for annealing temperatures below 550°C. In addition, we observe a complex interplay of polarization source terms associated with the exciton and Urbach band tail for annealing temperatures below 550°C. These experiments shed light on the carrier dynamics and ultrafast nonlinear optical properties of LT-GaAs.

Highlights

Control of the Urbach band tail and interband dephasing time with postgrowth annealing in low-temperaturegrown GaAs
The unique characteristics of this material that make it attractive for such applications stem from the incorporation of up to 0.6% excess arsenic during growth.[16]. This excess arsenic leads to a high density of Asi and AsGa point defects and associated midgap states[11,16] as well as local potential fluctuations that lead to spatially localized states below the band gap.[17]
Our experiments show that four-wave mixing (FWM) spectroscopy provides a sensitive probe of the defect distribution in low-temperature-grown semiconductors, providing an avenue for tailoring these defects for applications such as saturable absorbers and THz switching devices

Summary

Introduction

Control of the Urbach band tail and interband dephasing time with postgrowth annealing in low-temperaturegrown GaAs. This feature is highlighted, which shows the FWM spectrum from the as-grown LT-GaAs sample, alongside the response from HT-GaAs. An abrupt change in the signal characteristics occurs at an annealing temperature of 550◦C: The interband continuum response grows substantially relative to the exciton signal, and the band tail contribution is strongly reduced.

Results

Conclusion