CARBON RICH a-Sij.,Cx:H FILMS: AN INVESTIGATION ON RADIATIVE RECOMBINATION PROPERTIES F. GIORGIS', F. GIULIANI., C.F. PIRRI°, P. MANDRACCI#, P. RAVA*, R. REITANO', L. CALCAGNO P. MUSUMECI 4 Dipartimento di Fisica ed UnitA dell' Istituto Nazionale per la Fisica della Materia del Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy #Dipartimento di Elettronica ed Unit•. dell' Istituto Nazionale per la Fisica della Materia del Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy * Elettrorava S.p.A., Via Don Sapino, Savonera Torino, Italy 4 Dipartimento di Fisica ed Unit, dell' Istituto Nazionale per ]a Fisica della Materia dell' Universiti di Catania, C.so Italia 57, Catania, Italy ABSTRACT Amorphous silicon-carbon a-Sil.xCx:H films with x in the range 0.3-1 have been deposited by PECVD of SiH 4 +CH 4 and SiH 4 +C 2 H 2 gas mixtures. Photoluminescence characterizations have been performed, together with optical measurements. The dependence of radiative recombination properties as a function of x and as a function of damage introduced by H+-ion irradiation has been presented and correlated with the changes in the absorption spectra. INTRODUCTION Amorphous silicon-carbon alloys (a-Si 1 _xCx:H) are interesting materials both from fundamental and technological point of view. Due to the possibility to form Si-Si, Si-C, C-C, Si-H and C-H bonds and the tetrahedral or trigonal C configurations, silicon-carbon materials can have a variety of topological structures which affect the electronic density of states (DOS) and optical properties [1,2]. For what concerns the technology, a-Si 1 .xCx:H films were for many years interesting for optoelectronic applications such as solar cells, phototransistors and protective or passivation layers [3]. The discovery that a-Si 1 _xC,:H systems present high radiative recombination efficiency even at room temperature opened a wide field of applications such as active layers in electroluminescence devices [3]. However, the processes responsible for radiative recombinations and the influence of film structure, defects and DOS distribution still are open questions. In this paper we present results deduced in a-Si 1 .xC,:H samples at high carbon content grown by ultra high vacuum Plasma Enhanced Chemical Vapor Deposition (PECVD) of SiH 4 +CH 4 and SiH 4 +C 2 H 2 gas mixtures. Optical and luminescence properties have been investigated and will be discussed as a function of carbon content in the alloys. A change in defect densities has been induced by irradiating the samples with hydrogen ions. A correlation between irradiation doses, optical properties and light emission of the samples has been observed. EXPERIMENTAL a-Si .-Cx:H films were deposited by 13.56 MHz PECVD, of SiH 4 +CH 4 , at 200 and 350 'C substrate temperature and of SiH 4 +C 2 H 2 , at 200 and 280 'C substrate temperature, respectively, with several gas fluxes, with r.f. power density of 40 mW cm- 2 and 14 mm electrode distance. The deposition conditions have been chosen to optimize the optoelectronic properties of the materials, in particular of the photoluminescence efficiency. 261 Mat. Res. Soc. Symp. Proc. Vol. 507 © 1998 Materials Research Society