Abstract
We investigated effects of base pressure
$(P_{\rm base})$
of the deposition chamber on electrical properties and
defect states of amorphous In-Ga-Zn-O (a-IGZO) thin films deposited
by pulsed laser deposition. The impurity hydrogen concentration was
increased by an order of magnitude when
$P_{\rm base}$
was deteriorated
from
$<{{10}}^{-5}$
to
${{10}}^{-3}\
{{Pa}}$
. The optimum oxygen partial pressures
$(P_{\rm O2})$
were
2–4 Pa for an optimized deposition condition with the good
$P_{\rm base}$
;
on the other hand, off-optimized and/or poor
$P_{\rm base}$
require
much higher
$P_{\rm
O2}$
. This result provides an experimental evidence
for a charge compensation model by excess oxygen for H-containing
a-IGZO. Thermal desorption spectra indicated that the impurity hydrogens
originate mainly from water molecules in the residual gas and exist
as -OH chemical bonding states in the a-IGZO films. Hard X-ray photoemission
spectroscopy revealed that these -OH states form deep defects above
the valence band maximum.
© 2014 IEEE
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