Recently experimental evidence have been obtained, by optical absorption meas-urement~ with polarized light (4 1C) that GaSe has an indirect energy gap (1, 2),

Photovoltaic and photoconductive spectra have been measured at various temperatures and with various electrode mountings on p‐ and n‐type GaSe samples. The spectra have been also analyzed for various polarization states of the exciting light. Relaxation times of photovoltaic signals in both types of samples have been measured by using a Q‐switched ruby laser. The results allow to estimate for the first time the diffusion length of the minority carriers and the mobility along the c‐axis. Furthermore, some information has been obtained on the absorption structure of GaSe for energies less than the fundamental gap.

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Photoluminescence, photoconductive and photovoltaic measurements have been performed on ZnIn2S4 between 80 °K and RT. The experimental results agree with absorption data and previous luminescence measurements. A quantitative analysis of photoconductivity gives an estimate of the μτ‐product and diffusion length L.

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