The barrier layer at a free surface of a PbI, crystal surrounded by a non-polar gas has been found to exhibit pronounced voltage rectification when passed by an alternating current of constant amplitude Io. The rectified voltage Us is found proportional to I:, and its temperature dependence at low temperatures is of the form 1/T. The rectification may be quenched by weakly absorbed light in a certain wavelengths range. The light-induced relaxation of U , has a half-life time t l / z = to exp u/kT where u is the activation energy.There is direct proportionality between Us and the ambient gas pressure P, but the pressure dependence of t i p is of the form P -W . Heat treatment of PbI, enhances, while iodine vapour suppresses Us and t 1 / 2 . Correlation of this behaviour with ion adsorption-desorp tion processes is pointed out. On avait trouv6 que la couche barrikre sup une surface libre d'un cristal PbI, entour6 par un gaz non-polair montre une rectification de voltage prononcbe lorsqu' elle est traversbe par une courant alternatif d'amplitude constante I,. Le voltage rectifib Us est proportionnel iL I:, e t son d6pendance de la temperature (basses temperatures) a la forme 1/T. La rectification peut atre eteinte par une lumiere faiblement absorbbe, comprise dans une bande des longeurs d'onde. La relhchement de U s produite optiquement, a un temps de demie-vie t1/2 = to exp ulkT, o h u est l'energie d'activation. I1 y a une proportionnalitb directe entre U s et la pression P de gaz ambiant, mais la dbpendance de tlp de pression a la forme P-1/2. Le traitement thbrmique de PbI, augmente U s et t 1 / 2 , tandis que la vapeur d'iode supprime tous les deux. La correlation de la conduite observbe avec des processus adsorption-desorption ionique est indiqube.
Some observations are reported on voltage rectification across a barrier layer at a free surface of a high-resistivity CdS crystal traversed by a low-frequency alternating current of small constant amplitude. The rectified voltage is found to depend sensitively on the nature of the ambient gas and to quench out completely in the presence of traces of vapours of alcohols. It is confirmed that chemisorbed oxygen is largely responsible for the surface charge in crystals surrounded by atmospheric air. In addition to chemical quenching of rectification, optical quenching due to photodesorption is observed at a critical wavelength (outside the fundamental absorption band) which is characteristic of the ambient gas. The temperature dependence of the rectified voltage in the range -20-80°c exhibits a sharp drop above room temperature which may be interpreted as due to a decrease of barrier resistance rather than to thermal desorption. At low temperatures the rectified voltage is inversely proportional to the absolute temperature, in accordance with theoretical prediction.
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