Modulated Reflectance Spectroscopy of CdTe-Cd 1-x Mn x Te Multiple Quantum Wells and Superlattices Grown By Pulsed Laser
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MODULATED REFLECTANCE SPECTROSCOPY OF CdTe-Cd1,.MnTe MULTIPLE QUANTUM WELLS AND SUPERLATTICES GROWN BY PULSED LASER EVAPORATION AND EPITAXY D. LABRIE* AND J.J. DUBOWSKI** *Department of Physics, Dalhousie University, Halifax, N.S., Canada B3H 3J5 "Institute for Microstructural Sciences, National Research Council of Canada, Ottawa, Ontario, Canada KlA 0R6 ABSTRACT Piezoreflectance and photoreflectance spectroscopies have been used to investigate the electronic properties of CdTe-Cd1 5xMnxTe (x - 0.10) multiple quantum well and superlattice structures grown by Pulsed Laser Evaporation and Epitaxy (PLEE). The structures with the CdTe well widths from 54A to 245A have been investigated. The spectra exhibit a series of signatures which are attributed to free exciton transitions occuring between the heavy-hole and light-hole bands and the upper electron subbands within the CdTe well layers. The spectra indicate that the PLEE grown structures are of an excellent quality typical of the best currently available material. INTRODUCTION The magneto-optical properties of Cdt.xMnxTe(CMT) have stimulated a sustained interest in the study of this material [1]. The large Zeeman splitting of the exciton and the giant Faraday rotation observed in this material make CMT an excellent candidate for optoelectronic applications such as optical modulators and magnetic field sensors. Recently, it has been suggested (2] and then observed [3] that multiple quantum well (MQW) and superlattice (SL) structures formed with CMT layers have drastically enhanced magneto-optical properties compared to bulk-like CMT layers. Cd 1 .xMnXTe-based MQW and SL structures have been successfully grown by Molecular Beam Epitaxy (MBE) [43 and more recently by Pulsed Laser Evaporation and Epitaxy (PLEE) (5]. The free exciton (FE) quantum confinement has been observed in both MBE- and PLEE-grown material [6-9]. In this study, we apply modulated reflectance spectroscopy to a wide variety of CMT based MQW and SL structures grown by PLEE. The FE signatures are identified using a simple Kronig-Penney type model. These results clearly demonstrate that PLEE is an alternative to MBE for the growth of high quality CMT based MQW and SL structures. EXPERIMENTAL PROCEDURE We have used photoreflectance (PR) and Piezoreflectance (PzR) spectroscopies toward the study of the PLEE-grown samples. The photomodulation was obtained by using a chopped 5 mW He-Ne laser beam. The piezomodulation was accomplished by mounting the samples onto a specially designed leadzirconate-titanate transducer [10]. Mat. Res. Soc. Symp. Proc. Vol. 285. 01993 Materials Research Society
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The induced sinusoidal strain in our sample was - 3 x 10.5 rms. The modulated reflectance was analysed using standard lock-in techniques. The modulated reflectance normalized to the direct reflectance was measured as a function of wavelength using a grating spectrometer. RESULTS AND DISCUSSION The parameters of the four MQW and SL structures used in this study are given in table I. The PzR spectrum of sample CCM-11
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