# Step-like spectral distribution of photoelectrons at the percolation threshold in heavily $p$-doped GaAs

## TL;DR

This study investigates the origin of a step-like feature in the photoluminescence spectrum of heavily p-doped GaAs, linking it to the percolation threshold in the conduction band and analyzing electron spin dynamics.

## Contribution

It provides experimental evidence connecting the spectral step to the percolation threshold and distinguishes two electron ensembles with different spin relaxation times.

## Key findings

- The spectral step is controlled by the Fermi-Dirac distribution and energy distribution of photoexcited electrons.
- Two electron ensembles with spin lifetimes of 20 ps and 280 ps are identified.
- Electron states above the percolation threshold are rapidly relaxed, affecting the emission spectrum.

## Abstract

We study the origin of the step-like shoulder on the high energy side of the low temperature photoluminescence spectrum of heavily $p$-doped GaAs. We show experimentally that it is controlled by the Fermi-Dirac distribution of the holes and by the energy distribution of the photoexcited electrons showing a sharp step-like dependence. This step is attributed to the percolation threshold in the conduction band separating localized from delocalized electron states. A comprehensive set of optical techniques based on spin orientation of electrons, namely the Hanle effect, time- and polarization-resolved photoluminescence, as well as transient pump-probe Faraday rotation are used for these studies. We identify two different electron ensembles with substantially different spin lifetimes of 20 and 280~ps, limited by the lifetime of the electrons. Their spin relaxation times are longer than 2~ns. The relative contribution of short- and long-lived photoexcited electrons to the emission spectrum changes abruptly at the high-energy photoluminescence step-like tail. For energies above the percolation threshold the electron states are empty due to fast energy relaxation, while for lower energies the relaxation is suppressed and the majority of photoelectrons populate these states.