A. Rolland et al., ELECTRICAL-PROPERTIES OF AMORPHOUS-SILICON TRANSISTORS AND MIS-DEVICES - COMPARATIVE-STUDY OF TOP NITRIDE AND BOTTOM NITRIDE CONFIGURATIONS, Journal of the Electrochemical Society, 140(12), 1993, pp. 3679-3683
The electrical properties of silicon nitride/amorphous silicon structu
res were investigated using thin film transistors (TFTs) and metal ins
ulator semiconductor (MIS) devices employing either a top nitride (TN)
or bottom nitride (BN) as gate insulator. The density of states (DOS)
deduced from the subthreshold transfer characteristic of the TFTs is
one to two orders of magnitude higher than that obtained from quasista
tic C(V) measurements on the MIS structures. This difference is discus
sed by considering the different thickness of the a-Si:H layers of the
two devices and the role of a fixed charge at the rear interface. Bot
h techniques indicate a DOS in BN devices which is only slightly lower
than in TN devices, by less than a factor of two. The measured field
effect mobility of BN TFTs is about 70% higher. The differences in the
measured field effect mobility for TN and BN configuration are discus
sed and ascribed to the source and drain parasitic resistances. The co
nclusion is verified by the fabrication of a TN TFT with a pure phosph
ine rear surface treatment, which exhibits performance comparable to B
N TFTs.