No abstract

The energy gaps at 300 and 96 K of CuIn5S8 and AgIn5S8 single crystals were determined from the optical absorption measurements. The peaks of the photoconductive spectra observed at 300 and 77 K were in good agreement with the energy gaps. The resistivity and the mobility for the samples with less sulphur than the stoichiometric one were determined from the electrical measurements.

Optical absorption spectra of CuInSe2 single crystals were measured for the samples with −0.150≤x≤0.053, where x represents a degree of nonstoichiometry in the formula Cu1−xIn1+xSe2. The Urbach’s tail was observed for all samples between 90 K and room temperature. The Urbach’s energy, which represents an arbitrary intensity of exciton–phonon interaction, was almost constant for the Cu-rich samples (x<0), while it increased with increasing In composition for the In-rich ones (x≳0). Such an increase of the Urbach’s energy was explained to be due to enhanced electronic distortion caused by the compositional deviation from stoichiometry in terms of simultaneous influence of electron–phonon interaction and structural disorder.

The electrical resistivity and Hall effect of p- and n-type CuInSe2 single crystals are measured in the temperature range from 80 K to 500 K. p- and n-type samples are prepared by doping with excess Se and excess In, respectively. The acceptor levels at 0.020 eV and 0.028 eV above the valence band and the donor levels at 0.012 eV and 0.18 eV below the conduction band are identified. The mobility data are analysed assuming scattering by acoustic, polar optical, and nonpolar optical phonons and by ionized impurities. For some of the n-type samples, the measurements are extended to liquid helium temperature and the result is analysed by the existing theories of impurity band conduction.

The Raman-scattering spectra of I-III-VI2 group chalcopyrite semiconductors and their solid solutions were measured. The frequency relationship for the A1 vibrational mode agrees with the simple ratio of the anion atomic weights, although it also depends on the mean atomic weights of the cations. Compositional change of the A1 mode frequency for their solid solutions with anion substitution can be explained by the probability of formation of two pairs of anion atoms.