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In recent papers was shown the possibility to explain several electrical properties of amorphous GeSe films assuming the existence of depletion regions near the electrode interfaces (1, 2). On the other hand if such barriers exist there may be conditions making the influence of these b a r r i e r s negligible, i . e. , for appropriate values of bias, frequency, and temperature bulk properties can predominate (1,3,4).In this paper it will be shown the necessity of taking into account such a behaviour for the explanation of isothermal relaxation currents through Al-a-GeSe-A1 sandwich samples (sputtered a-GeSe and evaporated A1 filmscf. reference (2)) after the application of different voltages. After the application of a constant voltage U to such a sample the current reaches a steady-state value only after a long time. This phenomenon will be called "polarization behaviour" because after removing the bias a "depolarization current" occurred, proving the existence of ?n internal electrical field.Typical room temperature polarization currents of a representative sample for different voltage steps a r e shown in Fig. 1. If the voltage step i s low enough, a decreasing current i s observable (Fig. 1, curve a). In the low voltage range the relaxation charges Q evaluated from the polarization and depolarization chrrent , respectively , a r e equal and there i s a significant asymmetry of the current-voltage (I-U) characteristic. Similar results obtained from measurements on A1-CeF -A1 samples a r e reported by Nadkarni and Simmons (5). The relaxation behaviour was explained by the time-dependent growth of a depletion region by the liberation of electrons from deep localized states into the conduction band in the region Ls x Lsu (see Fig. 2).r 3 Nadkarni and Simmons (5) reported for higher voltage steps a saturation of the relaxation charge Q plotted a s a function of the bias, but not a qualitative change r

The temperature, illumination, frequency, and photon energy dependences of the photoconductivity in a-GeSe films are investigated. The conduction activation energy is 0.95 eV, the photoconductivity edge lies at 1.4 eV. The photoconductivity is field-independent up to 3 x lo4 V/cm and independent of the frequency of the chopping light up to at least 108 Hz

The optical behaviour of modified GeSe:Fex‐films (0 ≦ × ≦ 0.1) prepard by co‐sputtering is investigated using transmissionmeasurements and a new algorithm for the determination of the optical constants. An increase of the rfractive index and a nonlinear shift of the absorption edge to lower energies due to the increase of the Fe concentcation are observed. The results can be interpreted by a decrease of the bond strength, an increase of the densityof valence electrons, and an increase of the density of states neaar th mobility edges. For the interpreation of the shift of the absorption edge a density of states model (DOS mode) is proposed. In accordance with results of eletrical investigations it is supposed that the increase of the density of states near the mobilityy dege influences the electrical conductivity by modification, too.