FORMATION OF SELF-ASSEMBLING II-VI SEMICONDUCTOR NANOSTRUCTURES DURING MIGRATION-ENHANCED EPITAXY

We have studied the transition from two- to three-dimensional (3D) gro wth during migration enhanced epitaxy (MEE) of CdSe on ZnSe by systema tically varying the CdSe thickness. Transmission electron microscopy ( TEM) images show structures that contain islands within the quantum we ll (QW) region when the CdSe exceeds a critical thickness. The transit ion td a 3D interface could be confirmed by high-resolution X-ray diff raction (HRXRD) measurements. (0 0 4) diffraction profiles could be si mulated assuming flat interfaces only for CdSe below the critical thic kness. Photoluminescence (PL) shows emission energies up to 2.7 eV for flat QWs while samples with CdSe layers above the critical thickness show a broad emission around 2.3 eV. Photoluminescence excitation (PLE ) measurements from the latter samples support the assumption that CdS e islands within the QW region act as a final centre of recombination. Heterostructures containing a CdTe or a ZnTe layer have been investig ated for comparison. (C) 1998 Elsevier Science B.V. All rights reserve d.