Tem Study of Defects In CdTe/CdMnTe Superlattices on (100) InSb
- PDF / 944,941 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 83 Downloads / 156 Views
TEM STUDY OF DEFECTS IN CdTe/CdMnTe SUPERLATTICES ON (100) InSb SJ.DIAMOND AND J.W.STEEDS Bristol University, Department of Physics, Tyndall Ave., Bristol BS8 ITL, UK D.ASHENFORD AND B.LUNN Hull University Department of Engineering and Computing, Cottingham Rd., Hull, UK ABSTRACT CdTe/Cd 1- Mn Te superlattices with well/barrier thicknesses ranging from 20A to 300A were examined via plan and cross section TEM in analytical instruments capable of EDX and CL. Misfit dislocations, inclined dislocations and stacking faults were observed with a net density of around 109cm-2. It was observed that the dislocations originated near the substrate/epilayer interface and that stacking faults appeared preferrentially on the pair of (Ill)B (tellurium terminated) planes in the growth direction rather than on the (I I I)A planes. It is suggested that this is due to a difference in mobility between a and P dislocations originating at or near the substrate. INTRODUCTION II-VI semiconductors are becoming important as their large band-gaps are suited to optoelectronic devices such as solid state lasers and optical detectors. Furthermore, dilute magnetic semiconductors (DMS) such as CdMnTe offer additional applications as the interaction between their electronic and magnetic properties produces large magnetooptical effects such as magnetically tunable band gaps [1]. Molecular beam epitaxy (MBE) growth techniques allow high quality epilayers to be grown, including quantum well and superlattice structures which exploit two dimensional confinement effects for band gap tailoring purposes, and have been found to be strong photo-emitters. This study involves CdTe/Cdl xMnxTe superlattice structures grown on (100) InSb at Hull University. Values of x were near to 0.2 and quantum well thicknesses varied between 20 and 300A . InSb was chosen as the substrate material for its good lattice matching with both CdTe (approximately 0.02% mismatch at 25°C) and Cd.1 Mn Te (approximately 0.45% at 25"C for x=0.2). Furthermore high quality InSb is available which is suited to low temperature MBE growth [2], reducing the interdiffussion of layers. Samples of the CdTe/CdMnTe system have been examined in both cross section and plan view transmission electron microscopy (TEM), with both orientations revealing extensive detail. A typical sample consists of a (100) InSb substrate on which a 1000A CdTe buffer layer is grown, followed by a 2000A CdMnTe isolating layer. This CdTe buffer layer has been found to be critical to layer quality [2]. Superlattices comprising of wells and barriers of equal thickness, between 20 and 300A for different samples, with an overall thickness of about 1500A are then grown on this base. A second 2000A CdMnTe capping layer is finally grown to allow manganese composition determination by photoluminescence (PL). The (100) p-type InSb substrates were chemically cleaned and surface oxide was removed in vacuo using argon ion milling and growth temperature thermal anneal cycles until C(8x2) surface reconstruction was observed using is situ
Data Loading...
