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The electrical and optical properties of CuGaTe2 single crystals were investigated by resistivity and Hall effect measurements in the temperatur range T = 77… 300 K and optical transmission measurements in the temperature range T = 20… 300 K at photon energies hν = 1.15…1.50 eV. All samples were p‐type conducting due to shallow acceptors with ionization energies EA1 ≈︁ 10−3 eV and concentrations NA1 ≈︁ p = (2…4). 1018 cm−3. The absorption spectra could be described by simultaneous consideration of acceptor ‐ to ‐ conduction band transitions with EA2 = 360 meV and NA2 ≈︁ 1022 cm−3 and valence band ‐ to ‐ conduction band transitions with EG = 1.24 eV at room temperaure. The temperature coefficient of the fundamental edge is dEG/dT = −4.0. 10−4 eV/K. The results are discussed with regard to some general trends found in the Cu‐III–VI2 compounds.

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Several members of the I-ILI-M2 compound family have recently received considerable interest because of their potential application in photovoltaic devices. Particularly, very promising results have been obtained for solar cells and photodiodes based on CuInSe, (/l/ and references therein). In this connection it is of some interest to investigate mixed crystal systems with CuInSe, as one of the constituents. The properties of various authors /2 to 4/ but so far nothing is known about the system CuInl,xGaxSe2 although the difference in the lattice constant ratios of CuInSe2 and CuGaSe2 is only A(c/a) = 0.046 /5/ and, therefore, complete miscibility can be expected /6/. In the present communication we report some results concerning the preparation and the optical properties of CuInl,xGaxSe2 in the composition range 0 S x S 0.5.The samples used in the investigations were grown from corresponding mixtures of the prereacted alloy constituents or of the pure elements using a modified horizontal Bridgeman apparatus. The samples prepared by this technique were always polycrystalline, but single crystalline specimens with typical diameters of about 2 mm and thicknesses of about 100 pm suitable for the optical measurements could be selectively cut from the polycrystalline ingots. The composition of the samples w a s determined by electron beam microprobe analysis, X-ray diffraction measurements were performed to confirm the structure of the compounds and to determine the lattice constants. All samples had the chalcopyrite structure, and the lattice constants a and c obey Vegard' s rule within the accuracy of the measurements (Ax = e. 002, A a = = t0.02 8, Ac = 4 . 0 3 8) (see Fig. 1). The lattice constants of the alloy constituents are found to be in good agreement with published data /5/.have been studied by 1 physica (b)

The temperature dependence of the absorption edge in CuGaS2 is determined by absorption measurements in single crystals and thin films. A linear change of the gap energy Eg with a temperature coefficient of dEg/dT = − (2.2 ± 0.2) × 10−4 eV/K is found in the temperature range from 80 to 300 K. It is shown that the downshift in the absolute values of dEg/dT of the I–III–VI2 and I–VII compounds compared to their II–VI analogs can be explained by the p–d hybridization of the uppermost valence band.