Anisotropy of Optical and Electron Transport Properties of Atomic Ordering in CdGeAs 2
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** Air Force Research Laboratory, AFRLJMLPO, Wright-Patterson AFB 45433, OH, USA ***Institute of Theoretical Physics, Freiberg University of Mining and Technology, Cottastr. 4, D-09596 Freiberg, Germany ****Department of Physics, Michigan Technological University *****Departn•ent of Physics, St. Petersburg State Technical University, 29 Polytekhnicheskaya uL, St. Petersburg 19525 1, Russia ******Lockheed Sanders Inc., Nashua, 03061, NH, USA ABSTRACT
Inelastic light scattering by optical phonons and the temperature dependent electrical conductivity, Hall constant and photosensitivity were studied in oriented CdGeAs 2 crystals grown by ultra-low gradient freeze technique from near-stoichiometric melts. Observation of the clear polarization dependence of the inelastic light scattering spectra by optical phonons combined with the absence of any dependence of the intensity and frequency shift of the observed lines with mapping measurements in 300 ptm steps indicated the high optical quality and homogeneity of these single crystals. It is shown that surface-barrier structures using these single crystals may be used as wide-band detectors for natural light, as well as selective photoanalyzers for linearly polarized radiation.
INTRODUCTION The results of early systematic studies of the diamond-like ternary I-IH-VI 2 and H-TV-V 2 (ABC2 ) compound chalcopyrite semiconductors at the loffe Physico-Technical Institute have been summarized by Gorunova'. Since these early studies, the topic of chalcopyrite semiconductors has been a subject of intense research activity 2, 3'4 -5.6 7. 8.9. This activity was motivated by their extraordinary combination of attractive physical properties, particularly their large second order nonlinear susceptibilities and large birefringence which makes them the optimum choice for many nonlinear optical applications where Si or GaAs based devices are not suitable. They are isoelectronic analogs of the il-VI and III-V zinc-blende binary semiconductors. Both the electronic and lattice properties of chalcopyrite compounds show remarkable similarities with their cubic homologues and technologically important differences. There is a high current interest in chalcopyrite compounds for practical nonlinear optical applications in the areas of high-efficiency optical parametric oscillators and frequency up-' converters for the infrared range as well as for a wide spectral range optoelectronic devices 10,11.1213,14,15.16. We have recently succeeded in growing high crystalline quality ordered II-IV-V 2 chalcopyrite CdGeAs 2 by the improved horizontal ultra-low gradient freeze technique from near-stoichiometric melts. The CdGeAs 2 chalcopyrite structure (space group 142d) is the simplest non-cubic ternary analog of the cubic zinc-blende structure GaAs. The energy band structure of chalcopyrites 397 Mat. Res. Soc. Symp. Proc. Vol. 607 © 2000 Materials Research Society
differs from that of their binary analog in several nontrivial ways by virtue of their non-cubic structure. The Cd d-levels hybridize with the
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