At higher supply voltage the source/drain extensions are made with a lesser
dopant concentration (lightly doped drain, LDD) to limit the maximum
electric field in the vicinity of the drain. Otherwise hot-carrier
effects (HCE) would continually degrade the device.
If the LDD doping is too small for a given
an inversion channel
can form for
and
(quite similar to the inversion channel, but with reversed signs)
and the high electric field can cause a tunneling leakage current
from drain to bulk, i.e., gate-induced drain leakage (GIDL).
Another consequence of high voltages is the time-dependent dielectric
breakdown (TDDB) of the gate oxide, which becomes critical when
the electric field in the oxide exceeds 
As the distance between source and drain is reduced the potential
barrier at
between them starts to decrease,
which can be observed as a
decrease of the (somehow measured) threshold voltage (see
Section E.1 and Fig. E.3), a so-called
short-channel effect (SCE).
When the drain voltage is increased the depletion zone around the drain
increases and the electric field from the drain reduces the potential
barrier even further, which can be observed as an increased
drain-voltage dependent off-state current and as an increased output conductance in strong
inversion. This effect is called DIBL (drain-induced barrier lowering).
Both SCE and DIBL are among the main obstacles to technology scaling.
One way to reduce these effects is to introduce some halo doping
(the p+ regions in the vicinity of the gate edges) which
shapes the electrostatic potential in such a way, that the
channel-length dependence of
and
is reduced or even reversed
in some range of
.
Another group of phenomena affects the drivability directly.
The first one is velocity saturation, i.e., at large electric field
the drift velocity of carriers is no longer proportional to the field
but saturates at some saturation velocity
which is about 
for
electrons at a field of about 
.
The second effect is a degradation of the effective mobility 
at a large transversal field at the interface, i.e., for large
(the actual origin of this effect is somewhat unclear and may
also be linked to quantization phenomena in the channel [80]).
As a consequence of both of these phenomena, at higher supply voltages
the relative improvement of drivability and speed with voltage
is much lower than for small
.