d study is made of the electrical conductivity, u, the thermo e.m.f., a, and the Hall constant, R, in single crystals of Cu,Se. The temperature dependence of these phenomena in the range 22 to 650°C is also investigated. From the temperature dependence of u a value of 1.2 eV is found for the activation energy, AE, in the inherent region, whereas the value obtained from the optical absorption edge is 1.3 eV.n0JIyseHHbIe MOHOKPHCTanJIbI CU,Se, UCCJIeJlOBaHbI 3JIeKTpOIIpOBOJlHOCTH -U , TePMOBACa, 3@@eIFT XOJIJIa -R, U U X TeMIIepaTypHaR 3aBUCUMOCTb B UHTep-URH L\E B CO6CTBeHHOa 06JIaCTH HaBJleHO 1,2 3B, a U3 HpaR OIITIWeCKOrO IIOI'JIO-IqeHHII 1,3 38.

Single crystals of p-Cu,S are obtained with a hole concentration of 7.4~10'*cm-~, a mobility of 25 cmp V-ls-l, and a thermoelectric power of 90 mV/deg. The electrical conductivity, thermoelectric power and Hall effect are measured between 20 and 000 OC. A jump due to structural transformetions is observed in the temperature dependence of these parameters at 125 and 480 O C . The activation energy is found to have a value of 1.8 eV for the intrinsic range of the Conductivity, the value found for the extrinsic range being 0.064 ev. Cu$ is a scantily investigated semiconductor. The great energy gap (AE w w 1.8 eV), high melting point (T, = 1130 "C), mechanical strength, and autoalloying at the expense of structural imperfections make this material an interesting object for investigations.C%S has three modifications, namely a stable low-temperature phase with a rhombic lattice up to 105 "C, a high-temperature phase with a hexagonal lattice [1, 21 above this temperature, and a cubic modification of the compositon Chl.&3 above 480 O C resembling Cues, [3].C h S is a p-conducting material both in thin and massive specimens. Elsewhere the electric conductivity a, the thermo-e.m.f. u, the Hall effect, and the heat capacity of polycrystalline C b S have been measured between 20 and 600 OC. T w o anomalies due t o phase transformations have been found in these parameters. If there is a deficiency of sulphur the electric conductivity of CU$ decreases. I n the case of stoichiometry the activation energy for impurities amounts to 0.062 eV, the concentration of holes is 2.4 x 1010 ~r n -~, and the mobility is equal to 12 cm2/Vs [4, 51.Depending on disturbances of the stoichiometry thin layers of Cuss with nand p-type conductivity have been obtained by vacuum evaporation [7].Investigations on the transfer phenomenon in thin and massive specimens of polycrystalline Cu2S have been carried out [8], but no anomalies in Q and a have been found at the transition point from the rhombic modification to the hexagonal one. There is also a discrepancy between the values for the parameters obtained by different workers [4, 6, S, and 111.5 Phvica 28/1

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