Environmental Engineering Reference
In-Depth Information
Figure 7.2
A photograph of solar cells fabricated with different dimen-
sions to test the effects of the scaling-up process. See also Colour Insert.
7.3.1
Electrical Properties Under Dark Conditions
The dark current-voltage (I-V) curves of these devices show
excellent rectification properties. The breakdown voltages in the
reverse-bias mode extend beyond 45 V, showing the strength of the
rectifyingstructures.Theidealityfactors(
n
)varyintherange1.41-
2.26, and the
φ
b
values estimated using I-V curves with the lowest
values of
n
are greater than 1.60 eV (see Table 7.1). The accuracy
of
φ
b
depends on the value of
n
and, therefore, the conclusion made
by these measurements is that the potential barriers that exist in
thesedevicesaregreaterthan1.60eV.Thesevaluesof
n
indicatethe
presence of the R&G mechanism in the current conduction process
underdark conditionsevenintheseepitaxiallygrown materials[7].
This highlights the effects of the R&G process on devices, fabricated
φ
b
Table 7.1 Typical values of
n
and
measured under dark conditions
Device Parameters
φ
b
(eV)
Diode Number
n
1
1.41
>
1.60
2
1.50
>
1.56
3
1.68
>
1.48
4
1.84
>
1.43
5
2.26
>
1.27
