v . I. GAVRILENK03) (a), A. v. POSTNIKOV4) (a), N. I. KLWI (b), and V. G. LITOVCHENKO (b)The electroreflection spectra of hexagonal polytypes of Sic, 4H and 6H are measured in the range 1.0 to 5.6 eV. The energies of direct optical transitions are determined using a multiple oscillator model. The electronic band structures of three hexagonal polytypes of Sic (2H, 4H, and 6H) are calculated by the first-principles self-consistent linear muffin-tin orbital (LMTO ASA) method. One-electron energies and densities of states are obtained in the range & 15 eV around the top of valence band. The results calculated are compared with experimental data measured in this work and those available in the literature. Elektroreflexions-Spektren von hexagonalenSic-Polytypen 4H und 6H werden im Bereich 1,0 bis 5,6 eV gemessen. Die Energien der direkten optischen Ubergange werden mit Hilfe des Viel-Oszillator-Modells bestimmt. Die elektronische Bandstruktur von drei hexagonalen Sic-Polytypen (2H, 4H und 6H) wird aus ersten Prinzipien mittels LMTO-ASA-Methode berechnet. Einelektronen-Energien und Zustandsdichten werden im Bereich f 15 eV beziiglich der Valenzbandkante berechnet. Die Resultate werden mit experimentellen Daten verglichen, die sowohl in dieser Arbeit, als auch in der Literatur gemessen werden.

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(b), and E. V. MIKHAILOVSKAYA (b) Results are given of the experimental investigation of exciton absorption spectra in superthin films of PbI, deposited on various substrates (glass, mica, metal). A theory of exciton states in thin polar films is developed, on the basis of which excitonic and band size effects are analyzed. The theory is in qualitative and quantitative agreement with the experiment.Exzitonenabsorptionsspektren werden in ultradiinnen Pb1,-Schichten auf verschiedenen Substraten (Glas, Glimmer, Metall) untersucht. Eine Theorie der Exzitonenzustiinde in diinnen polaren Schichten wird entwickelt, auf deren Grundlage Exzitonen-und Band-Size-Effekte analysiert werden. Die Theorie stimmt mit dem Experiment qualitativ und quantitativ iiberein.

The photoluminescence spectra and radiation kinetics for various surface treatments of GaAs crystals were investigated at 20 °K. It is shown that the cleavage of the samples along {110} direction in liquid hydrogen leads as well to the decrease of nonradiative surface recombination as to the appearance of surface radiation. Surface luminescence is also observed for surfaces coated with Si3N4 films.