Raman scattering and photoluminescence in the tetrahedrally coordinated semiconductors and their heterostructures: II-VI semiconductors and chalcopyrites
Abstract
A Raman study of vibrational excitations was carried out in epilayers of cubic Cd$\sb{1-x}$Mn$\sb x$Se and Cd$\sb{1-x}$Zn$\sb x$Se. In the bulk CdSe exhibits the wurtzite (hexagonal) structure but when grown by molecular beam epitaxy (MBE) it exhibits a novel zinc-blende (cubic) phase. The modified random isodisplacement model was used to account for the experimental results; this model has been generalized to mixed crystals containing more than three different atomic species. A reflectivity and photoluminescence study of Cd$\sb{1-x}$Mn$\sb x$Se and Cd$\sb{1-x}$Zn$\sb x$Se epilayers was carried out to determine the x-dependence of the energy gap in the zinc-blende modification of these alloys. Spin-flip Raman scattering in epilayers of cubic Cd$\sb{1-x}$Mn$\sb x$Se, including the range of high-x values not available in bulk, has shown evidence of antiferromagnetic interaction between Mn$\sp{2+}$ ions. The photoluminescence spectra of Zn$\sb{1-x}$Cd$\sb x$Se/Zn$\sb{1-y}$Mn$\sb y$Se superlattices show confinement effects and Zeeman shifts which are compatible with theoretical calculations. The k $\cdot$ p based transfer matrix method, which includes the effect of strain, yields information about band offsets. Raman signatures of folded acoustic phonons are observed indicating a high structural quality of the superlattices studied. A spin-flip Raman scattering study of Cd$\sb{1-x}$Mn$\sb x$Te epilayers grown by Liquid Phase Epitaxy (LPE) indicated that high quality epilayers of doped diluted magnetic semiconductors (DMS's) can be grown using LPE. Vibrational Raman scattering in AgGaS$\sb2$ and AgGaSe$\sb2$, I-III-VI$\sb2$ chalcopyrites with $D\sbsp{2d}{12}$ symmetry, is studied. Preliminary experimental results on $\rm CdGa\sb2Se\sb4$, a II-III$\sb2$-VI$\sb4$ ordered vacancy compound (OVC), are also presented. These studies are motivated by the interest in tetrahedrally coordinated DMS's based on chalcopyrites, OVC's and related structures.
Degree
Ph.D.
Advisors
Ramdas, Purdue University.
Subject Area
Condensation|Optics
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