Ca. Dimitriadis et al., LEAKAGE CURRENT OF UNDOPED LPCVD POLYCRYSTALLINE SILICON THIN-FILM TRANSISTORS, I.E.E.E. transactions on electron devices, 42(5), 1995, pp. 950-956
The leakage current of thin-him transistors on undoped polycrystalline
silicon layers, deposited by low-pressure chemical vapor deposition,
is investigated in relation to the deposition pressure. For films depo
sited at pressure 40 mTorr, the leakage current I-L is controlled by t
he intrinsic resistivity of the film. The increase of the current I-L
with increasing the gate and drain bias voltages is due to the Joule-i
nduced-heating effect. For films deposited at pressures below 40 mTorr
, the leakage current is controlled by the reverse-biased junction at
the drain end. In this case, the minimum leakage current is modeled as
thermal generation current arising from midgap Coulombic defect trap
states. When the gate and drain bias voltages are increased, the therm
ally generated current is enhanced by the Poole-Frenkel effect due to
high electric fields at the drain junction. Such high electric fields
at the drain end can arise from doping inhomogeneities because of fast
diffusion through the grain boundaries of the implanted drain dopant.
At high bias voltages, a deviation from linearity of the Poole-Frenke
l current-voltage characteristics is observed due to the hot carrier e
ffect.