Raman scattering and photoluminescence in the tetrahedrally coordinated semiconductors and their heterostructures: II-VI semiconductors and chalcopyrites

Rodrigo Gregorio Alonso, Purdue University


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.




Ramdas, Purdue University.

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