Carbon Rich a-Si 1-x C x :H Films: An Investigation On Radiative Recombination Properties
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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 * 4
Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy Elettrorava S.p.A., Via Don Sapino, Savonera Torino, Italy 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+C2H 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-Si1 _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-Si1 .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-Si1 .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+C2H 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+C2H 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 photolumines
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