In-plane optical anisotropy due to conduction band electron wavefunctions

TL;DR

This study investigates how conduction band electron wavefunctions' symmetry causes in-plane optical anisotropy in photoluminescence from a 2DEG in Be-doped GaAs/AlGaAs heterostructures at low temperatures and magnetic fields.

Contribution

It introduces the idea that conduction band electron wavefunction symmetry leads to in-plane optical anisotropy, supported by quantitative analysis and qualitative arguments.

Findings

The degree of circular polarization decreases with increasing 2DEG concentration.

Stark effect on photoexcited holes is negligible in this context.

The in-plane anisotropy is attributed to the $C_{2v}$ symmetry of conduction band electron wavefunctions.

Abstract

Photoluminescence measurements were carried out on Be $\delta$-doped GaAs/Al$_{0.33}$Ga$_{0.67}$As heterostructure at 1.6 K in magnetic fields ($B$) up to 5 T. Luminescence originating from recombination of a two-dimensional electron gas (2DEG) and photo excited holes localized on Be acceptors was analyzed. The degree of circular polarization ($\gamma_C$) of the luminescence from fully occupied Landau levels was determined as a function of $B$ and the 2DEG concentration, $n_s$. At $B$ constant, $\gamma_C$ decreased with the increase of $n_s$. Two mechanisms of the $\gamma_C(n_s)$ dependence are discussed: a) the Stark effect on a photo excited hole bound to Be acceptor and b) the in-plane anisotropy of the intensity of optical transitions. A quantitative analysis shows that the influence of the Stark effect on $\gamma_C$ is negligible in the present experiment. We propose that the $\gamma_C(n_s)$ dependence results from the $C_{2v}$ symmetry of conduction band electron wavefunctions and we give qualitative arguments supporting this interpretation.