Structure, photoconductivity, photovoltage, and trap distribution in cathode-sputtered polycrystalline thin CdTe films are investigated. It is shown that the structure of these films depends on the temperature of the substrate and on the voltage during sputtering. From thermally stirnulated depolarization current (TSDC) measurements following photopolarization and from thermally stimulated current (TSC) measurements the existence of a trap level a t 0.34 eV is deduced.Struktur, Photoleitung, Photospannung und Vorteilung von Einfangstellen in kathodenzerstaubten, polykristallinen CdTe-Schichten werden untersucht. Es wird gezeigt, dalj die Struktur dieser Schichten von der Temperatur der Unterlage nnd der wahrend der Zerstaubung angelegten Spannung abhangt. Aus Messungen von thermisch stimulierten Depolarisationsstromen (TSDC) nach vorheriger Photopolarisierung sowie von thermisch stiniulierteii Stromen (TSC) folgt die Existenz von Haf tstellen, die bei 0,34 eV liegen. Sample PreparationThe samples were deposited1) by cathode sputtering (two electrodes) of CdTe in an argon atmosphere onto glazed ceramic substrates. The sputtering target was polycrystalline CdTe. The vacuum before starting the sputtering was better than 6.5 x x lop4 Pa, the anode-cathode distance was 3 to 5 em and the applied voltage 4 kV. The Structure1) of CdTe FilmsCdTe belongs to the AIIBV1 group of semiconductors and is characterized by partly ionic, partly covalent chemical bonds [l].CdTe may crystallize in two basic crystallographic modifications : the cubic zincblende structure (a = 0.648 nm) and the hexagonal wurtzite structure ( a = 0.457 nni, c = 0.747 nm). Actual CdTe crystallites contain many types of structural defects and their combinations. Stacking faults may also be present within the crystallites which contain regions with zincblende and wurtzite structure, respectively. Sometimes polytypes are formed in which the stacking sequence of atoms is repeating periodically over longer distances than in the basic zincblende or wurtzite structures.Every of the above-mentioned structures is polar. This means that the crystallites have different properties along the [hkZ] and the [hki.Z] directions, respectively. CdTe thin films containing a mixture of these crystallographic modifications are composed of crystallites forming parallel layers of the individual crystallographic modifications ; between them there are heterojunctions (barriers).Preparation and structure investigation of the samples were performed in Bratislava.

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The problem of the current–voltage characteristics of thin semiconducting films has been investigated. The sandwich configuration of films with metal electrodes was used and measurements were performed by increasing and decreasing the current and voltage, respectively. It is shown that there is a hysteresis of the current–voltage characteristics in such dynamic regimes, caused by temperature changes in the samples. In the case of a current source a negative resistance of S‐type can occur, whilst the appropriate characteristics for the voltage source are of a monotonously increasing type. An experimental verification of the theoretical results is given for the sandwich structure metal–(thin film of the amorphous semiconductor CdTe)–metal.

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