semiconducting nanowires may act as rapid onedimensional
charge transport bridges in the active channel.
3.2. Effect of Si nanowire loading on FET performance
Fig. 3 shows the saturation eld effect mobility, ON and OFF
current, and threshold voltage of the dual layer SiP3HT FETs with
varying nanowire density. The density (N) of dropcasted de
positions of Si nanowires ranges from 0 to 0.4 (nanowires per
10 10 mm2), while 10e20 devices for each density have been
characterized. Table 1 summarizes the transistor parameters
measured for pristine P3HT FETs and dual layer SiP3HT devices.
The measurement results of dual layer SiP3HT FETs are found to
consistently exhibit preferred performance compared to those in
the pristine state. As shown in Fig. 3a, there is an increase in eld
effect mobility as Si nanowire density increases from 0.05 to 0.4,
reaching a mean value of 4.5 102 cm2V1 s1 (maximum:
4.7 102 cm2V1 s1); this represents an improvement by a factor
of six over pristine P3HT. The ON/OFF current ratios of all devices
with or without Si nanowires are on the same order of 104105
(Fig. 3b). As the loaded Si nanowires within the semiconducting
layer are far below the percolation limit, the apparent mobilities
and ON/OFF current ratios are still determined by the conjugated
polymer. Fig. 3c shows threshold voltages (Vth) as a function of
nanowire loading. A negative Vth shift was observed from 3.5 V
(without nanowire, N ¼ 0) to 8.2 V (with nanowire, N ¼ 0.4) with
increased Si nanowire density (see the solidsquares). It is likely
that these nanowires serve as alternative pathways to evade those
unfavorable charge traps and grain boundaries inside the polymer
matrix, leading to an increased overall speed of charge carrier
transport. As a result, threshold voltage reduces and device
mobility enhances.
Moreover, the phenomenon of hysteresis is also investigated
from their transfer characteristics. The gate bias is swept from 20 V
to 40 V (forward) and then returns to the initial bias (backward).
Interestingly, the IDSVGS curves show that with the addition of Si
nanowires in the active channel the hysteresis loop is gradually