We recently discovered that in an AlF3/SiO2/Si structure extrinsic electrons are trapped at fluorine (F) vacancies in AlF3 at the
interface with SiO2, generating a high sheet density of fixed negative charges.
p- and n-Type Si substrates were oxidized using rapid thermal oxidation (RTO) or furnace oxidation (th); some samples were
passivated in hydrogen (H2). AlF3 was deposited onto oxidized Si wafers by a modified PVD process, leading to a F deficiency
(AlFx). Samples were characterized by mercury probe (Hg) CVand microwave photo conduction decay (mW-PCD), determining
charge and trap densities and effective carrier lifetime teff, respectively. An effective charge density of up to |Qeff¼ 6.9
1012 cm 2 is reached due to electrons tunneling from Si into AlF3, occupying F vacancies. Lifetime scans of p-type float zone
(FZ) Si samples with 1.5 nm RTO and 20 nm AlF3 show an increase in effective minority carrier lifetime by a factor of 8.4
compared to samples with 1.5 nm RTO only. The fixed negative charge density increases with exposure time to sunlight or at
simulated ageing by a 24 h anneal at 200 8C in air.
# 2004 Elsevier B.V. All rights reserved.