SPACE-CHARGE EFFECTS IN TYPE-II STRAINED-LAYER SUPERLATTICES

The low-temperature photoluminescence (PL) spectra of a range of CdS-C dSe and CdS-ZnSe type-II superlattices was measured under bath cw and quasi-cw excitation over the excitation range from mW cm(-2) to MW cm( -2). In all cases, a single PL band due to the recombination of separa ted electrons and holes in the type-II bandstructure was observed. As the excitation density increases from a low value, the PL peak shifts logarithmically towards the blue. Total shifts of up to 200 meV for a CdS-CdSe sample of 10 nm period are observed, with a corresponding shi ft-factor of 30 meV per decade of excitation density. The shift factor increases in a regular fashion with the superlattice period. A compar ison with the literature shows that a logarithmic dependance of the bl ue shift with increasing excitation density appears to be a universal feature of type-II SL, even in the absence of strain. (C) 1998 Publish ed by Elsevier Science B.V. All rights reserved.