Experimental Detection and Control of Trions and Fermi-Edge Singularity in Single-Barrier GaAs/AlAs/GaAs Heterostructures Using Photocapacitance Spectroscopy

Amit Bhunia,Shouvik Datta,Mohamed Henini,Y Galvão Gobato,Mohit Kumar Singh

doi:10.1103/physrevapplied.10.044043

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.

Highlights

Experimental study of neutral excitons and charged excitons like positively or negatively charged trions (X+ or X-) inside two dimensional (2D) semiconductor quantum structures are becoming important for understanding the many body physics of excitonic complexes [1,2] as well as for novel applications of excitonic devices [3]
We report that simple photocapacitance spectroscopy can be used to detect the specific signature of positively charged trions of indirect excitons (IX+) at moderate levels of carrier densities (1 1011 cm-2) in a single barrier GaAs/AlAs p-i-n heterostructure
As reported previously [18] for indirect excitons, the photocapacitance spectroscopy is shown to be sensitive to bias induced dipolar changes of indirect trions, FES formed across the AlAs barrier

Summary

INTRODUCTION

Experimental study of neutral excitons (say X0) and charged excitons like positively or negatively charged trions (X+ or X-) inside two dimensional (2D) semiconductor quantum structures are becoming important for understanding the many body physics of excitonic complexes [1,2] as well as for novel applications of excitonic devices [3]. According to theoretical predictions [10], binding energy of positively charged trions should be higher due to larger hole effective mass but experiments had reported nearly similar values of binding energies [11] for both X+ and X- At this point, we understand that identifying a trion as X+ or X- depends mostly upon how electrons and holes are being injected with applied bias based on the device configuration. We report that simple photocapacitance spectroscopy can be used to detect the specific signature of positively charged trions of indirect excitons (IX+) at moderate levels of carrier densities (1 1011 cm-2) in a single barrier GaAs/AlAs p-i-n heterostructure. These dipolar properties of excitonic complexes were mostly neglected in standard optical emission based spectroscopic techniques used in past studies to probe excitonic Bose-Einstein condensation (BEC) and excitonic lasing etc

SAMPLE AND EXPERIMENTAL METHODS

RESULTS AND DISCUSSIONS

Red shift and binding energy of indirect trions at 100 K

Differences in spectra at a fixed bias and with respect to temperature

CONCLUSIONS

References: