Polarimetry of photon echo on charged and neutral excitons in semiconductor quantum wells

S V Poltavtsev,Yu V Kapitonov,D R Yakovlev,I A Yugova,M Bayer,M Wiater,G Karczewski,T Wojtowicz,I A Akimov

doi:10.1038/s41598-019-42208-8

Abstract

Coherent optical spectroscopy such as four-wave mixing and photon echo generation deliver rich information on the energy levels involved in optical transitions through the analysis of polarization of the coherent response. In semiconductors, it can be applied to distinguish between different exciton complexes, which is a highly non-trivial problem in optical spectroscopy. We develop a simple approach based on photon echo polarimetry, in which polar plots of the photon echo amplitude are measured as function of the angle φ between the linear polarizations of the two exciting pulses. The rosette-like polar plots reveal a distinct difference between the neutral and charged exciton (trion) optical transitions in semiconductor nanostructures. We demonstrate this experimentally by photon echo polarimetry of a CdTe/(Cd, Mg)Te quantum well. The echoes of the trion and donor-bound exciton are linearly polarized at the angle 2φ with respect to the first pulse polarization and their amplitudes are weakly dependent on φ. While on the exciton the photon echo is co-polarized with the second exciting pulse and its amplitude scales as cosφ.

Highlights

Four-wave mixing (FWM) spectroscopy provides precise and distinct responses for the different energy level schemes of electronic systems
Polarization-dependent FWM on excitons in semiconductor nanostructures has been subject of extensive research for more than twenty years, the majority of studies has been performed in GaAs-based systems, such as quantum wells (QWs)[15,16,17,18]
In order to reveal differences in the polarization properties of the photon echoes on the different exciton complexes we study a 20-nm-thick CdTe/Cd0.76Mg0.24Te single QW

Summary

Introduction

Four-wave mixing (FWM) spectroscopy provides precise and distinct responses for the different energy level schemes of electronic systems. FWM and PE techniques involving laser pulse sequences with precisely controlled polarizations can be efficiently used as tool to study different exciton complexes such as neutral excitons[8], charged excitons (trions)[9,10,11,12], and biexcitons[13,14]. These techniques have been applied to investigate exciton localization[15], many-body interactions[16,17,18], and excitation-induced dephasing of excitons[19]. This unavoidably causes complex many-body interactions affecting the optical selection rules and causing excitation-induced dephasing that shortens the coherent dynamics of the studied optical states

Methods

Results

Conclusion