Negative photoconductivity in AgGaSe2 single crystals due to the negative photogalvanic effect

Abstract

AgGaSe2 is a representative of the c l a s s of ternary semiconductive compounds with the general formula A B (symmetry group 42m). I 111 VI C2 crystallizing in a chalcopyrite structure A s shown elsewhere /I/ ¶ AgGaSe2 is one of the materials holding much promise for non-linear optics. Owing t o a considerable linear electro-optic effect /2/, a high dark resistance and photosensitivity /3/, a high double-refraction index /4/ and optical activity of AgGaSe2 /5/, its crystals can be used as amplitude-type light modulators /6/ and media for recording threedimensional holograms, which generates interest in studying the photoelectrical properties of the crystals. The present report deals with the results of an investigation of the negative photogalvanic effect (NPGE) observed by the authors for the first time, and the impact of this effect on the negative photoconductivity (NP) in AgGaSe2 single crystals. The single crystals t o be studied were grown by the method of a gas-transport chemical reaction and had an n-type conductivity and a resistivity above 10 a m at 300 K. The single crystals obtained were needle-like in appearance and had m i r r o r surfaces. An In-Ga eutectic alloy was used to produce the electrodes. The average size of the crystals under study amounted t o 1~0 . 5~6 mm . 9 3 In o r d e r t o study the photogalvanic effect, the crystals were exposed t o linearly polarized light with the use of an SI-8 filament lamp and an MDR-2 monochromator. The signal was amplified by a V7-30 electrometrical amplifier and recorded by an Endim 621 -02-type recorder. The specimens to be measured were placed into a metal cryostat allowing t o vary the temperature from 100 t o 400 K under vacuum. The specimen temperature was measured by means 1) Prospekt Narimanova 31 A , SU-370143 Baku, USSR. 4 physica (a)