Surface Shubnikov-de Haas oscillations were studied in (0001) and (11̄00) accumulation layers of pure tellurium single crystals in external electric fields up to 106 V/cm. Whereas in accumulation layers of purely chemical origin at most two electric subbands could be identified, up to four subbands have been detected with the application of additional electric surface fields. The energies of the subbands were derived from the data and compared with a theoretical model assuming an exponential surface potential. The agreement is reasonably good, having in mind the complicated valence band structure of tellurium. The effective mass mc of the surface holes was determined from the temperature dependence of the amplitude of the quantum oscillations. It was found that mc had increased with respect to the bulk values. The Dingle temperature varied between 3 and 6 K for different samples.
The frequency dependence of the conductivity and permittivity of monocrystalline selenium was measured from 10 Hz to 2 GHz on the same samples, for the two orientations of the electric field parallel and perpendicular t o the c-axis, a t room temperature. The variations of 6 and e are significant. A unidimensional model, based on Volger's analysis for a n inhomogeneous dielectric, has been studied, assuming that the conductivity in selenium is controlled b y internal barriers. The high-frequency conductivity seems t o obey a more complicated model.Les mesures de la conductivite e t de la permittivitk du sklbnium monocristallin ont Btk faites sur une plage de frkquence Atendue (de 10 Hz h 2 GHz). Nous avons utilisk les mbmes bchantillons pour toutes les frkquences; le champ blectrique btait soit parallele soit perpendiculaire A l'axe ternaire d u cristal. Un modhle a btk calculi: en utilisant l'analyse d e Volger pour un diklectrique imparfait en supposant que la conductivitb dans le sklbnium est control6e par des barrihres. La conductivitk en haute frkquence semble obkir ?L un modele plus complexe.
The capacitance variations of a MOS structure versus polarization were calculated for 4.2 °K. Under these conditions the interface tellurium—tellurium dioxide is examined. Important trapping phenomena were observed and a rather large density of slow surface states determined (Ns = 9 × 1012 cm−2 eV−1). The density of fast surface states is smaller (Ns = 3 × 1011 cm−2 eV−1). Non‐equilibrium phenomena, shown by charging‐current measurement, lead to the suggestion that this is a general property of MOS capacitors at low temperatures, in the presence of trapping which also causes hysteresis.
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