Experimental evidences of trions and Fermi edge singularity in single barrier GaAs/AlAs/GaAs heterostructure using photocapacitance spectroscopy

TL;DR

This study demonstrates that photocapacitance spectroscopy can detect excitonic complexes, trions, and Fermi edge singularity in GaAs/AlAs/GaAs heterostructures at around 100 K, revealing different many-body physics compared to photoluminescence.

Contribution

It shows the effectiveness of photocapacitance spectroscopy in identifying trions and Fermi edge singularity at elevated temperatures, a technique seldom used for this purpose before.

Findings

Detection of excitons and trions via photocapacitance at ~100 K

Observation of a spectral transition from trions to Fermi edge singularity with bias

Photocapacitance reveals many-body effects not seen in photoluminescence

Abstract

In this paper, we show how photocapacitance spectra can probe two dimensional excitonic complexes and Fermi edge singularity as a function of applied bias around 100 K. In lower density regimes (<1x1011cm^-2), the appearance of two distinct peaks in the spectra are identified as a signature of coexistence of both excitons and positively charged trions. We estimate the binding energy of these trions as ~2.0 meV. In the higher density regimes (>1x10^11 cm^-2), we observe a sharp spectral transition from trions to asymmetric shaped Fermi edge singularity in the photocapacitance spectra around a particular reverse bias. However, these signatures are absent from the photoluminescence spectra measured under identical circumstances. Such dissimilarities clearly point out that different many body physics govern these two spectral measurements. We also argue why such quantum confined dipoles of spatially indirect trions can have thermodynamically finite probability to survive even around 100 K. Finally, our observations demonstrate that photocapacitance technique, which was seldom used to detect trions in the past, can also be useful to detect the traces of these spatially indirect excitonic complexes as well as Fermi edge singularity even at 100 K. This is mainly due to enhanced sensitivity of such dielectric measurements to dipolar changes within such heterojunction.