Henceforward, we focus on the later effect which consists of transferring of
the electrons emitted from the interface states towards the bulk. This effect is
not consistent with the present understanding of the charge pumping in MOSFETs.
It has been established in the literature that the minority carriers emitted
from the interface traps into the conduction band are collected by the source
and/or drain junctions. Therefore, they do not contribute to 
. This
assumption is adopted for the minority carriers
and 
in
Figures 3.16 show, however, that some part of the electrons
emitted from the interface states contributes to , thereby, it
increases . Figures 3.17
and 3.19 demonstrate that
current component is indeed directly correlated with the
interface state density at long 
.
component is independent of the interface state density
at short .
current which is dominant at short
, the component of at long depends only slightly on the
slope of the falling edge 
. It is moderately influenced by the
channel length, as is shown in Figure 3.19 where the same
amount of traps is positioned at the center of the channel of several
identical devices with only different gate length. Note that the component of
at short , which originates due to the remaining 
, is
independent of the trap density. We conclude that the geometric current
component in real MOSFETs occurs as a superposition of two independent effects:
An experimental evidence for these two processes is given in the sensitive
measurements of the geometric current component in [98]. Fig.4
in [98] shows evidently that 
does not vanish for long ,
while it increases rapidly for smaller than some threshold value, in real
MOSFETs. Note that the present calculations are even in a nearly quantitative
agreement with these measurements.
The transfer of the emitted carriers towards the bulk occurs at the onset of
the hole accumulation on the interface. If a significant portion of the traps
recombine with the incoming holes the novel effect represents only a small
correction of in the order of a few 
. However, this effect occurs
near the onset of accumulation when the hole capture is still small as well.
In these cases, the is comparable with 
. As a consequence,
this effect modulates the falling edge of the 
characteristics,
as is obtained in the calculations shown in Figure 3.18.
In this example, the geometric component which originates from the due to
fast turn-off is negligible (
for 
device).
The finding that the novel effect produce a stretch-out of the falling edge of
the curve in a lin-log scale has a minor practical importance,
since this part of the characteristics is never used to extract some
information.
In the three-level techniques, however, the novel effect can be relevant if the
mid-level 
is sufficiently low. Particularly important is the so-called
capture mode of the three-level measurements [395][11], which is
employed to extract the cross-section of the capture process in addition to the
common cross-section in the emission [397][154]. In the capture region of
the operation during the mid-level 
, all conditions are fulfilled that the
emitted electrons transfer towards the bulk, but not towards the junctions,
as is adopted in the theoretical model of this technique. An example shown in
Figure 3.20 demonstrates the modulation of the capture-side
of the saturated-
versus characteristics by the current
. In the numerical calculation 
is assumed, which is
long sufficiently to achieve the steady-state conditions at the end of the
mid-level for all used. The same calculation is carried out for
this device, but without any interface traps. The obtained which
originates solely from the remained due to a short 
, is very small
(less than 
in the range 
) leading to the conclusion
that the effect shown in Figure 3.20 does not occur as a
consequence of the standard geometrical current component due to , but
because of the emission from the traps.
The novel effect can also influence the pulsed-interface-probing (PIP)
measurements [52][51]. In the PIP theoretical model it is assumed
that all electrons (minorities) which are emitted from the interface traps
move back to the junctions. The negative bulk current is measured which
consists exclusively of the holes emitted from the interface states during the
deep-depletion conditions at the interface (bottom-level duration). If some of
the electrons emitted from the traps are injected into the bulk, they
generate a positive bulk electron current introducing an error in measurements.
Note that the bulk hole current is very small in this technique. Although the
hole capture does not take place in this method, because 
is
sufficiently high, the transient effect due to a small depletion-region
shortening can cause the injection of some portion of the emitted electrons
into the bulk, as is observed in our calculations.
Up to now we have considered the falling edge of the gate pulses for 
-channel
MOSFETs or the rising edge for 
-channel devices. Regarding the rising edge
for -channel devices and the falling edge for -channel devices, our study
did not show any non-ideal behaviour, even at short switching times (
).
Finally, a comment should be given on the geometric component in SOI
devices [445][357]. The same effects which occur in the bulk MOSFETs
produce the geometric current component in SOI devices as well. Note that in
SOI gated-diodes (-
- diodes) the effective channel length is twice the
channel length in MOSFETs, causing that the effect is much more pronounced.
The injection of the minorities into the bulk has also been employed for the
operation of SOI MOSFETs in some applications [407][405]. In addition
to the minority carriers, a finite time for the response of the majority
carriers can be exposed in SOI devices, leading to the geometric current
component due to majority carriers, as well. The majority-carrier effects are
pronounced for both, the gated-diodes [445][357] and the SOI MOSFETs
with a side-added bulk contact [445], when the devices are made in a
thin film. Whether the geometric component is produced by the minority or the
majority-carrier effects depends directly on the conditions holding on the
back-interface (accumulation or inversion) [192].
