BYCdGeAs belongs to the group of ternary diamond-like semiconducting compounds 2 2 4 5 of the A B C type. A large nonlinear optical coefficient and wide phase-matching 2 range of CdGeAs (1, 2) promise this crystal to be very useful for infrared parametric interactions and efficient second harmonic generation. The energy band structure of CdGeAs2 has been calculated by the pseudopotential method at the highsymmetry points of the chalcopyrite Brillouin zone (3) and studied experimentally in the higher energy region from reflectance (4, 5) and electroreflectance (6, 7) spectra. At room temperature the values of the forbidden energy gap determined from absorption edge (8) and photoconductivity (9) measurements a r e 0.53 and 0.50 eV , respectively. 2In the present note the valence band structure of CdGeAs2 has been determined from electroreflectance spectra investigated with polarized light in the spectral region 0 . 5 to 1.2 eV. The electroreflectance measurements were carried out at room temperature by the electrolyte technique on p-type CdGeAs2 single crystals (p = 1~1 0 '~ ~m -~) orientated by X-ray diffraction. It should be noted that some deterioration of the reflecting surface of the samples occurred during the electroreflectance measurements,In the vicinity of the fundamental absorption edge the electroreflectance spectrum of CdGeAs (Fig. 1) shows three peaks labelled A, B, and C at 0.58, 0.74, and 1.02 eV , respectively (at 77 OK in spectra measured with unpolarized light these peaks were located at 0.65, 0.82, and 1.05 eV (10)). The peak A i s mainly pronounced for parallel polarization of light (i? II 3) with respect to the Z-axis of the chalcopyrite crystal. The next peak B appears only for light with 3 1 F. The peak C is seen for both polarizations of light but it is stronger for E 1 E. The peak A i s 2

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Microstructure, x-ray diffraction, and thermographic analyses were made of the physicochemical properties of alloys lying on the CulnTe2-CdTe line . The dependences of the electrical conductivity, the carrier density. the carrier mobility, the thermoelectric power, and the thermal conductivity on the composition were determined. The alloys with the compositions 0.8 > x > 0 were homogeneous and had the zinc-blende structure. Near the terminal compound CuInTe2' which had the chalcogenide structure, the alloys consisted of two phases: they contained fine second -phase inclusions. The predominant phase in the alloys with the compositions x >. 0.9 had 'the chalcopyrite structure. The phase diagram of the investigated system indicated the occurrence of polymorphic solid-state transformations. All the alloys had p-type conduction. The hole density and mobility in the ordered alloys were higher than those in the disordered compositions. The alloys with x < 0.4 were compensated.Investigations of four-component solid solutions formed between AIIB v1 and ternary chalcogenides on the basis of heterovalent substitution are of considerable scientific and practical interest. Rodot [1] prepared and investigated AIBIIIC¥I _AIIBvI solid solutions between AgInTe 2 , CdTe, and HgTe. Some of these solid solutions may be used in the fabrication of thermoelements and in infrared radiation detectors [2].We synthesized alloys located on the CuInTe2-CdTe line in the quaternary system Cu-Cd-In-Te, carried out a physicochemical analysis of these alloys, and investigated some of their physical properties. The line in question could be represented by a straight line AB lying inside the composition tetrahedron (Fig. 1).The charges used in the synthesis of the alloys were calculated from the formula (CuInTe2>X • (2CdTeh_x, deduced from the equimolar relationship between the two original components. The compositions of the charges were varied in steps of 10 mol.%, whereas close to CuInTe2 the steps were reduced to 5 mol.%. The elements from which the original compounds were prepared did not contain more than 0.005 wt.% impurities. The same conditions during the synthesis, crystallization, and annealing were ensured by placing all the ampoules of a given * "Crystals," pp. 413-416 (see page 3). 66

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