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Bandgap Fluctuations in Compensated a‐Si : H (P, B) Films
Author(s) -
Rath J. K.,
Fuhs W.,
Mell H.
Publication year - 1993
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221790110
Subject(s) - band gap , boron , diffusion , doping , analytical chemistry (journal) , materials science , glow discharge , absorption (acoustics) , fermi level , conductivity , deposition (geology) , electrical resistivity and conductivity , phase (matter) , chemistry , condensed matter physics , plasma , physics , optoelectronics , electron , thermodynamics , organic chemistry , chromatography , quantum mechanics , sediment , biology , composite material , paleontology
N‐type compensated films of a‐Si : H (P, B) and a‐Si : H (Li, B) are prepared by the glow discharge decompusition of SiH 4 . Doping is achieved from the gas phase by addition of PH 3 and B 2 H 6 or after film deposition by in‐diffusion of Li. The statistical shift of the Fermi level inferred from the temperature dependence of the dark conductivity is consistent with a pronounced minimum in the density of states distribution in the upper half of the mobility gap. This minimum apparently shifts towards midgap when the boron content of the films is increased. The optical absorption indicates a decrease of the bandgap and an increase of the Urbach‐tail parameter E t , with increasing boron content. Both the statistical shift and the changes in the optical absorption are explained in terms of an apparent broadening of the bandtails due to boron‐induced fluctuations of the bandgap.