Stability and Nanostrucure of Heterogeneous Amorphous Silicon Thin-Film Synthesized under High Chamber Pressure (500 to
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STABILITY AND NANOSTRUCURE OF HETEROGENEOUS AMORPHOUS SILICON THIN-FILM SYNTHESIZED UNDER HIGH CHAMBER PRESSURE (500 TO 2200 mTorr) REGIME OF RF PECVD A. R. MIDDYA1,2a, S. HAMMA1b, S. HAZRA2c, S. RAY2 AND C. LONGEAUD3 1 Laboratoire de Physique des Interfaces et des Couches Minces (UMR 7647 CNRS), Ecole Polytechnique, 91128 Palaiseau, Cedex, FRANCE; 2Energy Research Unit, Indian Association for the Cultivation of Science, Jadavpur, Calcutta - 70 032, INDIA; 3Laboratoire de Genie Electrique de Paris (CNRS, URA 0127), Ecole Superieure d′Electricite, Universites Paris VI et Paris XI, Plateau de Moulon 91192 Gif-Sur-Yvette, Cedex, FRANCE ABSTRACT We report on improvement in stability of a new type of amorphous silicon films, synthesized (growth rate > 0.1 nm/s) by driving the plasma condition close to the powder regime (or “γ-regime”) of rf PECVD. These films exhibit high mobility-lifetime products [(µτ)annld ∼ 104 cm2/V, σph/σd ∼ 5-10x105, Ea ≈ 0.7 - 0.9 eV ], compact network structure [CH ≈ 7 to 8 at%, nanovoid density < 0.01 %, ρ ≈ 2.23 ± 0.01 gm/cm3], new features of optical properties and density-of-state (DOS) above EF is significantly lower than that of state-of-the art films. The kinetics of light-induced (AM 1.5) degradation of µτ is very fast and saturated µτ ∼ 10-6 cm2/V, a value similar to that of conventional a-Si:H films at annealed state. The improved stability of “new” a-Si films, henceforth it will be denoted as “quasi-amorphous silicon (qm-Si) thinfilm”, will be correlated with its specific nanostructure.
INTRODUCTION The improved stability of high H-diluted a-Si:H materials or protocrystalline Si films compared to undiluted films convincingly demonstrates that microstructure of Si-Si network influences in a complex way defect creation process during light-soaking [1, 2, 3]. In other words, light-induced degradation (LID) is sensitivite to the details of Si-Si tetrahedral network structure, local smallscale ordering in addition to bonded hydrogen content and concentration of polyhydride bonds [(SiH2)n]. In this work, we report on another experimental evidence that how Si-Si network structure in amorphous matrix is important in determining LID metastability of a-Si:H films. These ‘new” type of amorphous silicon thin-film have been developed by running the plasma condition close to powder regime (γ′-regime) of radio frequency plasma-enhanced chemical vapor deposition (rf PECVD) which exhibit significantly improved stability compared to stateof-the-art a-Si:H films [4, 5, 6]. These films are amorphous and do not exhibit thickness dependence phase transition (as it happens in high H-diluted films), however complimentary strPresent address: a. Department of Physics, Syracuse University, Syracuse, NY 13244-1130, b. Novellus Systems, Inc., San Jose, CA 95134, c. Institute of Energy Conversion, University of Delware, Newark, DE 19716-3820.
A9.5.1
1.00E-04
1.5 1 0.5 0 0
500 1000 1500 2000 2500
2
2
Mobxlifetime (Cm /V)
-1
Dark Conductivity (Scm ),
Deposition rate (A/s)
2.5
1.00E-05 1.00E-06
Dark Co
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