Electrical and optical properties of amorphous Si_xN_1−x

Abstract

Abstract Amorphous silicon nitride films have been prepared by the glow-discharge decomposition of a wide range of ammonia/silane gas mixtures. In particular, samples prepared from mixtures containing very small amounts of ammonia have been investigated. The dark- and photoconductivities, the optical gap and the thermoelectric power have been measured as a function of the volume ratio of the deposition gases, denoted by R. A range of specimens has also been prepared in a junction configuration, and the electron and hole mobilities of these has been determined. The results of all of the measurements show a systematic and continuous variation with R. Extended-state conduction predominates throughout, and the majority carriers are electrons. For R < 5 × 10−3 it is believed that a shallow level of ionized donor states is introduced. This is supported by the sensitization of the photoresponse, the decrease in the conductivity activation energy and the decrease in the electron drift mobility activation energy. As R is further increased, a transition in electrical properties occurs, and the optical gap opens up. For R >3 insulating near-stoichiometric silicon nitride is produced.