Single crystals of L‐alanine have been grown from buffered aqueous solutions and characterised as to their optical quality via wavefront distortion analysis, electrooptical response and harmonic generation efficiency. Refraction indices as well as phase matching loci were found in satisfactory agreement with previously published data for crystals grown in non buffered solution. Estimates for the electro‐optical response are reported for the first time. The experimentally observed crystal habit is discussed in terms of morphological importance (M.I.), which was found to be in disagreement with the predictions of crystallographic criteria based on the interplanar distance dhkl, on the periodic bond chains (PBC) and the attachment energy Eatt. This disagreement is tentatively attributed to the presence of impurities and non‐appropriate supersaturation conditions.

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),

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p-CuGaSe2/n-CdS heterojunctions have been prepared by depositing CdS films on p-type CuGaSe2 single crystals whose initial resistivity was 10−2 Ω cm and changed to 1 Ω cm after the CdS film deposition. The CdS films, which were grown by a multisources method, exhibit a room-temperature resistivity of 0.1 Ω cm. The absolute quantum efficiency of these devices as photovoltaic detectors reaches the value of 80% at a wavelength of 5800 Å. As solar cells, these heterojunctions at 25 °C display a solar power conversion efficiency of 5% when they are exposed to the solar light whose intensity is 71 mW/cm2. When the heterojunctions are directly polarized, they emit light in a broad band which is centered at ∼7700 Å. An external electroluminescent emission efficiency of about 0.05% has been measured at liquid-nitrogen temperature.

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