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Hyrogenated Amorphous Silicon with High Growth Rate, Gas Utilization and Homogeneous Deposition by Amplitude Modulated Vhf-Pecvd for Solar Cell Application

Published online by Cambridge University Press:  01 February 2011

J.K Rath ,
A.C.W. Biebericher ,
R. Jimenez Zambrano ,
R.E.I. Schropp ,
W. F. van der Weg  and
W.J. Goedheer
J.K Rath
Affiliation:
Utrecht University, Debye Institute, Surface, Interface and Devices, P.O. Box 80000, NL-3508 TA Utrecht, the Netherlands
A.C.W. Biebericher
Affiliation:
Utrecht University, Debye Institute, Surface, Interface and Devices, P.O. Box 80000, NL-3508 TA Utrecht, the Netherlands
R. Jimenez Zambrano
Affiliation:
Utrecht University, Debye Institute, Surface, Interface and Devices, P.O. Box 80000, NL-3508 TA Utrecht, the Netherlands
R.E.I. Schropp
Affiliation:
Utrecht University, Debye Institute, Surface, Interface and Devices, P.O. Box 80000, NL-3508 TA Utrecht, the Netherlands
W. F. van der Weg
Affiliation:
Utrecht University, Debye Institute, Surface, Interface and Devices, P.O. Box 80000, NL-3508 TA Utrecht, the Netherlands
W.J. Goedheer
Affiliation:
FOM Institute for Plasma physics ‘Rijnhuizen’, P.O. Box 1207, NL-3430 BE Nieuwegein, The Netherlands.
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Abstract

Hydrogenated amorphous silicon samples have been deposited by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD), using a square-wave amplitudemodulated radio-frequency excitation. It is observed that the gas-utilization efficiency improves by a considerable amount when amplitude modulation is combined with a reduction in the gas flows. Using a conventional continuous wave (cw) 50 MHz plasma with SiH4 and H2 gas flows of 30 sccm each at a pressure of 0.2 mbar, the gas-utilization efficiency is about 8%. It increases up to 50%, by modulating the amplitude of the radio-frequency excitation signal and reducing both gas flows to 10 sccm, keeping the pressure constant. In this case, the deposition rate amounted to 0.55 nm/s; which is twice as large as compared to the deposition rate of a cw deposition. Device-quality opto-electronic properties are obtained under these conditions. The refractive index at 2 eV is about 4.25 and the microstructure parameter has a value around 0.02. The materials exhibited a low defect density (CPM) which is in the order of 3-8x1015 per cubic centimeter and photo-to-dark-conductivity ratio of 4-6x106. N-i-p solar cells of size 0.16 cm2 deposited on 10cmx10cm stainless steel (SS) substrate in the configuration SS/n-a-Si:H/i-a- Si:H/buffer/p-μc-Si/ITO/Ag grid (without back reflector) using amorphous silicon i-layer made by amplitude-modulated VHF plasma CVD showed an efficiency of 6.5%. This is a similar efficiency to the cell with standard device-quality cw a-Si:H in the same n-i-p structure, but at a high growth of 0.55 nm/s and gas utilization of ∼50%.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 715: Symposium A – Amorphous and Heterogeneous Silicon-Based Films-2002 , 2002 , A6.6
Copyright
Copyright © Materials Research Society 2002

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