Role of Power Density, U.V. Light and Hydrogen Dilution on Transition of Amorphous to Microcrystalline Structure on Film
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ROLE OF POWER DENSITY, U.V. LIGHT AND HYDROGEN DILUTION ON TRANSITION OF AMORPHOUS TO MICROCRYSTALLINE STRUCTURE ON FILMS PRODUCED BY A TCDDC SYSTEM M. Vieira, R. Martins, A. Maqarico, I. Bafa, F. Soares and L. Guimardes. Faculdade de Ci~ncias e Tecnologia da Universidade Nova de Lisboa/UNINOVA/Centro de Ffsica Molecular das Universidades de Lisboa (INIC), PORTUGAL.
ABSTRACT The role of deposition condition on content and bond configurations of a-Si:H/jgc-Si:H and a-Si:C:H doped films were investigated through IR spectra and correlated with transport properties. The microstructure, morphology, chemical composition and electro-optical properties were inferred from normal X-ray power diffraction, scanning electron microscopy (SEM), Rutherford Back Scattering (RBS), dark conductivity, visible and IR measurements. The films under investigation were prepared in a Two Consecutive Decomposition and Deposition Chamber (TCDDC[1]) system under various deposition conditions such as: power density, dp; H2 partial pressure; substrate temperature, Ts; electromagnetic static fields (fG and I) with or without U.V. light assisting the process.Transition of a-Si:H to g±c-Si:H (doped) films is accomplished by structure variation on bond configurations, hydrogen contents, CH, and transport properties. When oxygen is present during the deposition, films deposited with U.V. light assisting the process have 02 incorporated as Si--O while at high dp levels (without U.V. light) 02 appears in the matrix as Si-O bonds. Such behaviour is explained by changes on bond configurations and on the way how hydrogen is attached in the network. 1. INTRODUCTION Since the recent success in using a-Si films and its alloys as a true electronic material [2] the field of tetrahedral-bonded amorphous semiconductors has entered in a new phase, the so-called a-Si age. Since then, efforts have been put by several co-workers [3] in order to understand better the correlation between deposition parameters and film properties. For instance, is known that a-Si films produced by r.f. glow discharge present lower density of gap states than those ones produced by other techniques [4], when certain deposition conditions are achieved. Microcrystallization of such films is dependent on growth conditions, mainly related with hydrogen dilution and power densities used. Recently, photo-CVD [5] has been applied for producing a-Si films with good quality at high growth rates. Nevertheless little work has been performed concerning the use of U.V. light assisting the deposition process [6]. In this paper we shall discuss the role of power density, U.V. light and hydrogen dilution on performances and bond configurations presented by a-Si:H/tc-Si:H films and its alloys, produced by a TCDDC system [7]. 2. EXPERIMENTAL RESULTS Doped a/tc-Si:H films and alloys were deposited in a TCDDC system in presence of electromagnetic static fields, assisted or not by U.V. light [1], using a gas doping level of 2.5% for n-type and 2.5/3% for p-type films. Electro-optical properties, microstruct
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