Observation of charged excitons in V‐groove quantum wires

Abstract

We report on the observation of negatively and positively charged excitons in the photoluminescence spectra of V-groove quantum wires. The charged exciton binding energy increases with the strength of the quantum confinement. We demonstrate that the charged excitons are localized by the fluctuations of the confinement potential and estimate a minimal value of the localization length.Introduction Observation of charged excitons in the photoluminescence (PL) spectra of semiconductor quantum wires has until recently been hindered by inhomogeneous line broadening due to structural imperfections in high quality samples. A negatively charged exciton (X -) with a binding energy of 2.3 meV relative to the exciton line was identified, however, in a micro-photoluminescence study of a T-shaped QWR of improved quality [1]. This observation was made possible by the reduction of the PL linewidth to about 1 meV.In this paper we study the PL spectra of n-type modulation-doped and undoped GaAs/AlGaAs V-groove quantum wires (QWRs), in which the carrier density was tuned by applying a potential on a Schottky gate. In order to free oneself from the inhomogeneities of the wires, which are present on a length scale of 1 to 10 µm, we prepared samples with submicron apertures made through an opaque Aluminium film. Previous optical studies that were performed with this technique on similar and undoped QWR samples have evidenced sharp PL lines with about 140 µeV linewidth [2]. These spectral lines were ascribed to excitons recombining in the local potential minima created by structural disorder at the interface.