For vitreous antimony trisulfide films (thickness 6.4 to 16.1 pm) the steady-state current-voltage characteristics were measured. The currents proportional to U 2 are interpreted in terms of space-charge-limited currents (SCLC) with a single trap level. It is proved that a steep current increase a t the end of the square-law region is caused by trap filling. The values of the parameters of this trapping level calculated using two independent methodsfrom the temperature dependence of the reduction factor 8 and from the trap-filled limit (TFL) voltageare in close agreement. The polarization and the conduction mechanism of vitreous Sb2S, films a t lower temperatures are discussed.Es wurden stationare Strom-Spannungs-Charakteristiken an Schichten aus amorphem Sb,S, (6,4 bis 16,l pm) gemessen. Die Proportionalitat des Stromes zu U 2 d-, wird durch raumladungsbegrenzte Strome mit einem einzelnen Haftstellenniveau erklart. Es wird bewiesen, daB der scharfe Knick im Endbereich des quadratischen Teiles der Strom-Spannungs-Charakteristik bei der Spannung U Z -~ durch Fiillung des diskreten Haftstellenniveaus hervorgerufen wird. Die Parameter dieses Haftstellenniveaus wurden mit zwei voneinander unabhangigen Methoden bestimmt : aus der Temperaturabhangigkeit des Beduktionsfaktors 8 und aus der Analyse der Spannung U Z -~. Beide Methoden ergaben gute Ubereinstimmung. Die Polarisation und der Leitungsmechanismns von amorphen Sb,S,-Schichten bei niedrigen Temperaturen werden ebenfalls analysiert.

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The time-dependent current due to the drift of a small charge is investigated in an insulator with a single trap level. A theoretical study of multiple trapping gives the criteria to determine the transit time from the moment when the current is equal to 0.5 of its equilibrium value. A method to measure the thermal release time from the current relaxation which is due to charge ejection into the collecting electrode is proposed. The theoretical data are verified experimentally in high-polymeric vitreous selenium. om2. Die Ergebnisse bestatigen die Vorstellungen von der strukturellen Natur der Haftstellen, die die Driftbeweglichkeit beeinflussen. In1,roduc tionThe study of time-dependent flow of injected current in high-resistivity semiconductors can give valuable information on trapping centres. Many and Rakavy have numerically calculated trapping effects in case of transient space-chargelimited current and have found the latter useful to evaluate the time of carrier capture and that of thermal release [l]. For this purpose small-signal current transients are even more convenient : Blakney and Grunwald have obtained an explicit expression for the initial stage of current relaxation, limited to the condition that none of the drifting carriers reaches the collecting electrode [a, 31.Tefft has given the distribution functions of free and trapped charge for an arbitrary moment of time, and has derived some analytic approximations of time-dependent xerographic discharge [4].The correct measuring of the initia,l stage being difficult this paper proposes a useful analytic approximation for t'he last stage of current relaxation which is caused by ejecting previously multiple-trapped charge into the collecting electrode. The formulae obtained adequately describe the experimental data of high-polymeric vitreous selenium obtained from melt by rapid cooling. Evaporated amorphous selenium films hzve been repeatedly investigated [5 to 71. physic8 33/2