Chemistry Reference
In-Depth Information
Figure 3.19. XRD pattern of a thin film (thickness
-phase of
p
-NPNN HV-grown on a glass substrate. The inset shows the rocking curve of the
(004) reflection. Reprinted with permission from J. Fraxedas, J. Caro, J. Santiso,
A. Figueras, P. Gorostiza and F. Sanz,
Europhysics Letters
1999, Vol. 48, 461-467.
∼
1
m) of the
α
µ
exemplified for pentacene OFETs (Gundlach
et al.
, 1997). When deposited by
flash evaporation onto substrates held at temperatures between 293 and 433 K,
only very lowmobilities are obtained (
0001 cm
2
V
−
1
s
−
1
). Flash evaporation is
often used for organic semiconductor depositions to avoid problems with thermal
decomposition of the material being evaporated. Using rapid thermal annealing to
rapidly heat the fabricated OFETs to 623 K for a few seconds increases the field-
effect mobility to about 0.002 cm
2
V
−
1
s
−
1
. The initial poor mobility is clearly due
to poor molecular ordering in the flash evaporated film, and the mobility improve-
ment comes from an improvement in ordering with the anneal. However, ordered
films are obtained for depositions at low to moderate rates (0.1-0.5 nm s
−
1
) onto
substrates held at temperatures from 293 to 393 K. Relatively high mobility de-
vices are obtained for depositions over this entire range: typically 0.3 cm
2
V
−
1
s
−
1
,
with a maximum observed value of 0.7 cm
2
V
−
1
s
−
1
. Mobilities measured in thin
films have reached values as high as 1.5 cm
2
V
−
1
s
−
1
or more, a point that will be
discussed in Section 6.3 (see Table 6.1).
∼
0
.
Pulsed laser deposition
The pulsed laser deposition (PLD) technique is widely used for inorganic materials
but is becoming increasingly employed for the preparation of thin films of polymers
