Optical studies of carrier transport phenomena in CdSe/ZnSe fractional monolayer superlattices

Optical properties of short-period CdSe/ZnSe fractional monolayer (ML) supe rlattices (SLs) with nominal thickness of CdSe layers in the range of 0.1-2 ML have been studied, focusing on vertical carrier transport along the gro wth axis. Specially designed structures have been grown by molecular beam e pitaxy, containing either a single SL or a SL with an enlarged ZnCdSe quant um well located far away from the region where carriers are generated by ph oto-excitation. Extremely efficient vertical transport is observed for a Cd Se layer thickness less than 0.7 ML, confirming formation of a perfect mini band of extended states. Localized electronic levels appear in the SL with CdSe layers thicker than 0.7 ML. However, at layer thicknesses up to 1-1.5 ML the extended states dominate the light-absorption process and the transp ort properties of the SL. (C) 1998 Elsevier Science S.A. All rights reserve d.