The E 1 c reflectivity has been measured up to 10 eV for hexagonal, single-crystal GaN.The band structure and reflectivity have been computed by the empirical pseudopotential method and used to identify the observed spectral peaks.La rBflectivit6 E 1 c d'un monocristal de GaN hexagonal a 6t6 measure6 jusqu'8 10 eV.La structure de bande et la r6flectivitk ont 6t6 calculkes par la mkthode du pseudopotentiel empirique et ont 8th utiliseks pour identifier les cretes du spectre observ6.

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The consequences of layer compound polytypism on optical properties and electronic Die Auswirkungen der Schichtstruktur-Polytypie anf optische Eigenschaften und elek-band structure are investigated for the case of 2H and 4H PbI,.tronische Bandstruktur werden am Beispiel des 2Hund 4H-PbI, untersucht.