Numerical analysis of amorphous and
polycrystalline silicon semiconductor devices
This research activity, which started in 1991, is related to the
physics and numerical analysis of semiconductor devices and in
particular to the study of the electron-transport phenomena in
amorphous and polycrystalline semiconductors, which are strongly
influenced by the presence of bulk trap states.
The developed models have been inserted into the device simulator
HFIELDS and then applied to the analysis of thin-film devices.
The activity of 1995 dealt with these topics:
Generalization of the time-dependent analysis
in presence of localized states. The transport model incorporates two
more continuity equations for trapped electrons and holes; both free
and trapped charges dynamics is thus described. The simulator has been
used to study the current degradation in amorphous-silicon,
inverted-staggered MOS devices, related to the slowest charge
trapping processes in the device bulk. Performances of elementary
circuits (NMOS and CMOS inverters) have also been studied.
Generalization of the small-signal analysis.
Two distinct recombination functions have been used in the
small-signal continuity equations to take into account the exchange of
charge between trap states and band states in response to an applied
small-signal. The simulated C-V curves of gate-to-source and
gate-to-drain capacitance of an amorphous-silicon MOS device agree
well with measurements and show the influence of the trapped charge.
Inclusion in the model of field-dependent generation phenomena,
and in particular the band-to-band
tunnel generation, the phonon-assisted trap-to-band tunnel generation and
the Poole-Frankel generation. Simulations of polycrystalline
thin-film devices showed good matching with measurements and allowed
for a physical interpretation of the high leakage currents typical of these