Influence of MBE growth conditions on optical properties of CdTe/ZnTe quantum structures

Highly strained CdTe/ZnTe structures with extremely thin multiple quantum w ells (QWs) have been studied by photoluminescence (PL) in the temperature r ange 1.8-200 K. The structures with the wells nominally 1-5 monolayers (ML) wide were grown by molecular beam epitaxy with or without growth interrupt ion (CI) applied. Low temperature PL spectra consist of a single excitonic peak corresponding to the transition from the first electronic confined sub level to the first heavy-hole sublevel. With increasing width of the well t he PL peak shifts to lower energy, from 2.35 to 1.95 IV. The red-shift can be satisfactorily described within the envelope function approximation taki ng into account the band modifications induced by strain. In the case of QW s grown without GI the exciton dissociation is shown to be the dominant mec hanism responsible for the decrease of PL intensity with the increasing tem perature. In contrast, for structures grown with GI the quenching of the ex citonic emission is found to be caused by the thermal activation of the hea vy holes from the CdTe well into the ZnTe barrier region. This shows that t he non-radiative recombination on the interface imperfections is very effec tive in the case of QWs grown without GI. Additionally, the improvement of the interface quality by applying the interruption is also indicated by the strong reduction of the width of PL emission. The full width at half maxim um (FWHM) values obtained for samples grown with GI are of about two times smaller than those measured for QW's grown without applying GI technique. ( C) 2000 Published by Elsevier Science S.A. All rights reserved.