Conductivity and Hall effect were investigated on evaporated CdSe films either nontreated or annealed a t 400 and 700 "C. The measurements are performed in the temperature range from -150 to 400 "C. I n the lower temperature range the mobility of electrons follows an exponential temperature dependence of the form peff = po exp ( -A E / k T ) typical for polycrystalline films, which is not only determined by scattering mechanisms alone but also by the numbers and properties of potential barriers a t the crystallite boundaries. These properties of polycrystalline film structure also explain the dependence of conductivity and mobility on film thickness found in non-treated CdSe films. I n the high temperature range conductivity and electron concentrat,ion strongly increase, indicating a self-activated conductivity mechanism. The conduction electron concentration is determined here by thermal intrinsic disorder of lattice atoms.An unbehandelten und bei 400 und 700 "C getemperten CdSe-Aufdampfschichten wurden die Leitfahigkeit und der Halleffekt im Temperaturbereich von -150 bis 400 "C untersucht. I m niederen Temperaturbereich genugt die Beweglichkeit der Elektronen einer fur polykristalline Schichten typischen exponentiellen Temperaturabhangigkeit der Form peff = ,uo exp ( -A E / k T ) , die nicht nur diirch Streumechanismen allein, sondern auch durch die Zahl und die Eigenschaften der Potentialbarrieren an den Kristallitgrenzen bestimmt wird. Diese Eigenschaften der polykristallinen Schichtstruktur erklaren auch die a n nnbehandelten CdSe-Schichten gefundene Schichtdickenabhangigkeit der Leitfahigkeit und Beweglichkeit. I m Hochtemperaturbereich nehmen Leitfahigkeit und Elektronenkonzentration stark zu, was auf einen Eigenstorstellenleitungsmechanisnius hindeutet. Die Leitungselektronenkonzentration wird hier durch die thermodynamische Eigenfehlordnung der Gitterbausteine bestimmt.
In investigations of conductivity of semiconducting thin films it i s generally supposed that the concentration of electrons is independent of film thickness and that the mobility of electrons does not depend on film thickness if the mean free path of the electrons i s smaller than film thickness. Experimental results, e. g. on thin films of germanium (l), lead telluride (2). tellurium (3), and cadmium sulphide (4). in which a dependence of carrier concentration and mobility on film thickness was observed for t h i c h e s s e s up to 10 p m, show that this assumption is not always satisfied for thicker films, too. In the mentioned papers the investigations were performed on several specimens of different thickness obtained from different evaporations. Such specimens a r e commonly not identical in real structure.Therefore we have measured the conductivity in dependence on growing film thickness during evaporation. The thickness was determined by optical interference fringes. The glass substrate was held at a temperature of 160 O C .
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