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Evolution of Structural and Electronic Properties in Boron-doped Nanocrystalline Silicon Thin Films

Published online by Cambridge University Press:  01 February 2011

Hyun Jung Lee
Affiliation:
hyunjung@venus.uwaterloo.ca, University of Waterloo, Department of Electrical and Computer Engineering, 200 University Avenue West, Waterloo, N2L 3G1, Canada
Andrei Sazonov
Affiliation:
asazonov@venus.uwaterloo.ca, University of Waterloo, Department of Electrical and Computer Engineering, Waterloo, Ontario, N2L 3G1, Canada
Arokia Nathan
Affiliation:
anathan@ucl.ac.uk, University College Lodon, London Centre for Nanotechnology, London, WC1H 0AH, United Kingdom
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Abstract

We report on the boron-doping dependence of the structural and electronic properties in nanocrystalline silicon (nc-Si:H) films directly deposited by plasma- enhanced chemical vapor deposition (PECVD). The crystallinity, micro-structure, and dark conductivity of the films were investigated by gradually varying the ratio of trimethylboron [B(CH3)3 or TMB] to silane (SiH4) from 0.1 to 2 %. It was found that the low level of boron doping (< 0.2 %) first compensated the nc-Si:H material which demonstrates slightly n-type properties. As the doping increased up to 0.5 %, the maximum dark conductivity (ód) of 1.11 S/cm was obtained while high crystalline fraction (Xc) of the films (over 70 %) was maintained. However, further increase in a TMB-to-SiH4 ratio reduced ód to the order of 10-7 S/cm due to a phase transition of the films from nanocrystalline to amorphous, which was indicated by Raman spectra measurements.

P-channel nc-Si:H thin film transistors (TFTs) with top gate and staggered source/drain contacts were fabricated using the developed p+ nc-Si:H layer. The fabricated TFT exhibits a threshold voltage (VTp) of -26.2 V and field effective mobility of holes (μp) of 0.24 cm2/V·s.

Type
Research Article
Copyright
Copyright © Materials Research Society 2007

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