A CuInSe2 (CIS) bulk single crystal grown by the directional freezing method from the melt at 1250°C shows superior crystal quality, as evidenced by its (p-type) electrical properties. Photoluminescence at 1.5 K shows a strong and well resolved spectrum with fine structures never before observed from this compound. Free exciton emission exhibits a doublet structure which can either be described as a splitting due to the uniaxial crystal field or as a polariton. The energy gap of the CIS semiconductor as determined from the temperature dependence of the free exciton line is 1.058 eV. Two moderate free-to-bound transitions are assigned to VCu and CuIn acceptors. A weak PL peak corresponding to a deep level is interpreted as arising from the Sei acceptor. Strong phonon replicas are also observed for the first time in a CIS bulk single crystal. The phonon wavelength of 218–237 cm-1 is in good agreement with the reported Raman result of 233 cm-1 for the LO phonon.

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Equilibrium conditions for the alloy system (CUI _ xAgx)(Gal _ylny)(Se l _ z Tezb were determined throughout the complete range of composition. Polycrystalline samples of 125 different compositions, i.e., with x,y, and z = 0, 0.25, 0.5, 0.75, and l.0, were prepared by a melt and anneal technique. Different annealing temperatures in the range 6@..800 ·C were used depending upon the alloy composition and annealing times of up to 5 months used to attain equilibrium conditions. Debye-Scherrer x-ray powder photographs were used to investigate the equilibrium conditions. It was found that single phase chalcopyrite structure was obtained for all compositions of the copper (x = 0), indium ( y = 1), and tellurium (z = 1) sections but that miscibility gaps occurred in the silver (x = 1), gallium (y = 0), and selenium (z = 0) sections, and that these miscibility gaps extended through the general alloy system. Values oflattice parameters a and c were determined for all samples showing single phase condition and for each of the above sections the variations of a and c with composition were fitted to power series in the appropriate composition coordinates. Hence contours of constant a and constant c were determined. From the parameters for each section, general series expressions in x, y, and z were developed and the values from these compared with the experimental data for the general alloys. It is shown that a modified Weaire and Noolandi relation of the form [2 -(c/a)] = K (XI -XIII + qX VI f fits all of the experimental data. Averaged values of K and q were obtained by fitting separately to different sections of the alloy system and also to all alloys of the complete system.

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