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

Highly strained CdTe/ZnTe structures with extremely thin multiple quantum wells (QWs) have been studied by photoluminescence (PL) in the temperature range 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 interruption (CI) applied. Low temperature PL spectra consist of a single excitonic peak corresponding to the transition from the first electronic confined sublevel to the first heavy-hole sublevel. With increasing width of the well the 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 taking into account the band modifications induced by strain. In the case of QWs grown without GI the exciton dissociation is shown to be the dominant mechanism responsible for the decrease of PL intensity with the increasing temperature. In contrast, for structures grown with GI the quenching of the excitonic emission is found to be caused by the thermal activation of the heavy holes from the CdTe well into the ZnTe barrier region. This shows that the non-radiative recombination on the interface imperfections is very effective 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 maximum (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.