No abstract

No abstract

The surface of vapor−deposited GaN and the cross section of GaN light−emitting diodes were examined using secondary electron emission, cathodoluminescence, beam−induced conductivity, and beam−induced voltage. The GaN layer is an assemblage of identically oriented microcrystals. The Zn distribution in the insulating layer is usually not uniform. High built−in fields occur at the two edges of the insulating layer.

Optical density, dark conductivity, and photoconductivity of evaporated antimony triselenide thin films were studied as a function of deposition conditions. The film properties may vary appreciably with both source temperature and time at which the deposition is made. Initial deposits exhibit abnormal bandgap energies, as high as 1.7 eV with a source operated 20 deg below the Sb2Se3 melting point. The bandgap energy decreases monotonically with time during a long evaporation, finally approaching a constant value in the 1.1–1.2 eV range if the boat is maintained at or above the Sb2Se3 melting point (611 °C). The data suggest that initially stoichiometric Sb2Se3 fractionates during the early stages of evaporation, the Se-Sb ratio of the melt decreasing until a composition range producing films with constant bandgap energy is reached. Spectrographic analyses of different fractions from the vapor stream support this explanation.

Films of As2Se3 and Sb2Se3 and their mixtures have been studied by electron microscopy and diffraction. On heating amorphous As2Se3 films no change occurs, but the Sb2Se3 films and mixtures of Sb2Se3 and As2Se3 transform to give small single crystals. These crystals have their c axes parallel to the substrate and give mainly (010) and (100) planes normal to the beam. Rate of nucleation is independent of temperature, indicating nucleation from predetermined nucleation centers. Growth rate increases with increasing temperature, but involves very little migration of material, implying that surface migration is very slow.