Environmental Engineering Reference
In-Depth Information
with even the best semiconductor growth technique and improved
device structure. Even with highest internal electric field available,
the recombination process cannot easily be minimised due to the
presence of active R&G centres. The presence of high potential
barriers indicates the possibility of achieving large
V
oc
values from
these structures since
V
oc
is a function of
φ
b
, as given by Eq. 1.16.
The capacitance of the 0.5 mm diameter devices was also
measured at 1 MHz frequency, as a function of the DC bias voltage.
Mott-Schottky graphs were plotted in order to estimate the doping
concentration of the material layers at the edge of the depletion
region. A typical 1/C
2
versus V plot, shown in Fig. 7.3, indicates
an arc instead of the usual straight line observed for devices with
a uniform doping concentration. The doping concentration at the
edge of the depletion region at zero bias is 4
×
10
17
cm
−
3
,andthis
value shows a gradual change as the DC bias is applied to the device
structure. This gradual change of doping concentration is expected
from this device structure since it was intentionally introduced to
the system.
Figure 7.3
A typical Mott-Schottky plot observed for graded bandgap
devices, showingagradual changeinthedopingconcentration, asexpected
for this device.
