Direct and indirect excitons in semiconductor coupled quantum wells in an applied electric field

TL;DR

This paper presents a precise computational method for analyzing exciton states in coupled quantum wells under electric fields, revealing how exciton properties change with applied voltage and providing a publicly available simulation tool.

Contribution

It introduces an efficient algorithm for solving the Schrödinger equation in real space and offers new insights into exciton behavior in CQWs under electric fields.

Findings

Ground state switches from direct to indirect exciton at ~5 kV/cm

Exciton lifetime varies with electric field due to recombination and tunneling

Calculated lifetimes agree with experimental photoluminescence data

Abstract

An accurate calculation of the exciton ground and excited states in AlGaAs and InGaAs coupled quantum wells (CQWs) in an external electric field is presented. An efficient and straightforward algorithm of solving the Schrodinger equation in real space has been developed and exciton binding energies, oscillator strengths, lifetimes, and absorption spectra are calculated for applied electric fields up to 100 kV/cm. It is found that in symmetric 8-4-8 nm GaAs/Al(0.33)Ga(0.67)As CQW structure, the ground state of the system switches from direct to indirect exciton at approximately 5 kV/cm with dramatic changes of its binding energy and oscillator strength while the bright excited direct-exciton state remains almost unaffected. It is shown that the excitonic lifetime is dominated either by the radiative recombination or by tunneling processes at small/large values of the electric field, respectively. The calculated lifetime of the exciton ground state as a function of the bias voltage is in a quantitative agreement with low-temperature photoluminescence measurements. We have also made freely available a numerical code for calculation of the optical properties of direct and indirect excitons in CQWs in an electric field.