Regensburg 2004 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
DS: Dünne Schichten
DS 20: Dünne Schichten für die Photovoltaik II
DS 20.3: Vortrag
Donnerstag, 11. März 2004, 15:00–15:15, HS 32
Ultrathin hydrogenated amorphous silicon layers on crystalline silicon: a-Si:H gap state density distribution and a-Si/c-Si interface properties — •Lars Korte, Klaus Kliefoth, Abdelazize Laades, and Manfred Schmidt — Hahn-Meitner-Institut Berlin, Abt. Silizium-Photovoltaik, Kekuléstr. 5, 12489 Berlin
The application of hydrogenated amorphous silicon as emitter layer in
high-efficiency heterostructure solar cells requires an optimization of the
a-Si:H bulk and a-Si/c-Si interface electrical properties. Information on
these properties can be obtained by photoelectron spectroscopy (PES) and
the surface photovoltage technique (SPV), respectively. By PES, the Fermi
level Ef as well as the distribution of states Nocc(E) in the
valence band and the energy gap up to Ef can be measured [1]. The
information depth at the used low excitation energies
(hν=4−7 eV) increases to 5-10 nm, equal to the optimum
emitter thickness. Thus, Nocc(E) is an average of the a-Si:H density
of states (DOS). For samples of n-doped a-Si:H deposited on c-Si by
PECVD, Ef−Ev varies from 1.15 eV for undoped layers to a
saturation value of 1.47 eV at a doping of [P]=104 ppm in
the gas phase. Also, an increase of the Urbach energy from
51 meV to 101 meV and of the DOS at midgap is
observed, indicating an increase of disorder and dangling bond
concentration.
From SPV, the band bending at the a-Si:H/c-Si interface can be determined.
The interface gap states distribution Dit(E) is measured by bias
voltage-dependent SPV and proves the excellent passivation of the c-Si
surface by the a-Si:H network, with a Dit as low as that of
H-terminated c-Si.
[1] M. Schmidt et al., MRS Proc. 762, A19.11.1 (2003).