Effect of Hydrogen Dilution on Structure and Electronic Properties of Ge:H and Ge Y Si 1-Y Films Deposited by Low Freque
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0910-A07-02
Effect of Hydrogen Dilution on Structure and Electronic Properties of Ge:H and GeYSi1-Y Films Deposited by Low Frequency Plasma A. Kosarev1, L. Sanchez1, A. Torres1, T. Felter2, A. Ilinskii3, Y. Kudrjavtsev4, and R. Asomoza4 1 National Institute for Astrophysics, Optics ans Electronics, Puebla, 72000, Mexico 2 Lawrence Livermore National Laboratory, CA, 94550 3 Benemerita Universidad Autonoma de Puebla, Puebla, 72050, Mexico 4 CINVESTAV-IPN, D.F, 07360, Mexico ABSTRACT We report on a systematic study of growth rate, surface morphology, hydrogen and oxygen incorporation, optical and electrical properties in Ge:H and GeYSi1-Y:H, Y> 0.85 films, deposited in a capacitive reactor by low frequency PE CVD. Silane and germane were used as feed gases diluted by hydrogen. Hydrogen dilution is characterized by R= QH2/[QSiH4+QGeH4], where QH2, QSiH4, and QGeH4 are gas flows of hydrogen, silane and germane, respectively. The flow was varied in the range of R=20 to 80. Composition of the films was characterized by SIMS profiling. We did not observed a significant change of the deposition rate Vd in GeYSi1-Y:H films over the range of R, while for Ge:H films Vd was significantly reduced for R>50. AFM characterization of the surface morphology demonstrated that at R=50 average height (R) reached a maximum in both Ge:H and GeYSi1-Y:H films, while average diameter (R) had a minimum in GeYSi1-Y:H films and maximum in Ge:H films. Both Ge:H and GeYSi1-Y:H films demonstrated a change of E04 in the studied range of R, and a minimum clearly appeared in ∆E at R=50-60 suggesting significant reduction in weak bonds of these films. The activation energy of conductivity Ea slightly increases with R in Ge:H films and shows no definitive trend in GeYSi1Y:H: films. Both FTIR and SIMS data show a general trend of decreasing hydrogen and oxygen content with R. These two types of films showed different behavior and correlations between surface morphology and optical and electrical properties. INTRODUCTION Despite of many applications of plasma deposited GeYSi1-Y:H and Ge:H films, e.g. in multijunction solar cells [1,2], photo-detectors [3,4] and un-cooled micro-bolometers [5-7], structure and properties of these films have been less studied in comparison with silicon films. Earlier works can be found in several reviews [8,9]. Typically RF glow discharge at the frequency f=13.56 MHz is used for deposition of these films. However, deposition conditions that provide higher ion bombardment during film growth are considered to be favorable for deposition of good quality GeYSi1-Y:H and Ge:H films [10]. These conditions can be easily obtained in low frequency (LF) discharge. Growth and properties of GeYSi1-Y:H films deposited by LF PE CVD have been reported in refs. [11,12]. In the latter an effect of argon and hydrogen dilution (10:1 and 20:1, respectively) has been studied over the entire range of Ge concentrations. Preparation and study of nano-crystalline films by RF discharge with a very high degree of hydrogen dilution (from 170:1 to 400:1
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