H. Sehil et al., CHARACTERIZATION OF THE POLYSILICON THIN-FILM TRANSISTORS ELABORATED IN HIGH AND LOW-TEMPERATURE PROCESSES - STUDY OF THE DENSITY OF TRAPS, Synthetic metals, 90(3), 1997, pp. 181-185
The states density of traps (DOS) in the gap has been determined by a
study of the temperature influence on the field-effect conductance of
polycrystalline silicon thin film transistors fabricated in high and l
ow temperature technologies. The effect on the DOS value of the granul
ar structure, film thickness (between 50 and 150 nm) and technological
process has been investigated. On the one hand, for thin film transis
tors (TFTs) fabricated in a high temperature process, we observed that
, when the film thickness is greater than 50 nm, the DOS distribution
has a 'band tailing' with an exponential shape. The slope increases wh
en the thickness decreases. This indicates the enhancement of the diso
rder due to an important density of defects localized in the grain and
or in the grain boundaries. Moreover, for thin films (t(f)=50 nm), th
e DOS curve shows a characteristic hump which proves the presence of d
angling bonds. They are localized at 0.35 eV above the top of the vale
nce band. On the other hand, the effect of the low temperature process
produces particularities on the TFT DOS. The classical doped drain (C
DD) exhibits a high density of states with a classical distribution (b
and tailing with an exponential shape). However, the lightly doped dra
in (LDD) TFT DOS shows a hump localized at 0.4 eV below the bottom of
the conduction band. The difference observed on the DOS distributions
is related to the in situ doping level of the polysilicon-deposited th
in films. (C) 1997 Elsevier Science S.A.