Optoelectronic properties of hydrogenated amorphous silicon films deposited under negative substrate bias
作者:
P. Roca i Cabarrocas,
P. Morin,
V. Chu,
J. P. Conde,
J. Z. Liu,
H. R. Park,
S. Wagner,
期刊:
Journal of Applied Physics
(AIP Available online 1991)
卷期:
Volume 69,
issue 5
页码: 2942-2950
ISSN:0021-8979
年代: 1991
DOI:10.1063/1.348605
出版商: AIP
数据来源: AIP
摘要:
We present a detailed study of the effects of ion bombardment on the optoelectronic properties ofa‐Si:H films. Two series of samples were deposited from a rf glow discharge at 30 and 100 mTorr of silane pressure, corresponding to two different deposition conditions. The energy of the ions impinging on the substrate was increased by applying a negative dc bias in steps of 25 V to the substrate holder. The increase of the substrate bias from 0 to −100 V had no effect on the deposition rate ofa‐Si:H at 30 mTorr, whereas a factor of 2 decrease was observed for deposition at 100 mTorr. The density of states of thea‐Si:H films, determined by photothermal deflection spectroscopy and by the constant‐photocurrent method, decreased as the substrate bias was increased up to −50 V, especially for the series deposited at 100 mTorr. At the same time the valence‐band tail became sharper. These observations are consistent with the improvement of the electron drift‐mobility deep‐trapping‐lifetime (&mgr;d&tgr;d)eproduct, determined by time‐of‐flight, and of the hole‐mobility recombination‐lifetime (&mgr;&tgr;r)hproduct determined from the voltage dependence of the photocurrent collection efficiency. For both series of samples, the films with the best electronic properties were obtained at a negative substrate bias of 50 V. No correlation was found between the substrate bias and the light‐induced degradation behavior of these films. The saturated density of light‐induced defects shows a direct correlation with the optical gap.
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