Environmental Engineering Reference
In-Depth Information
stoichiometric CuInSe
2
material, 25% of the group-I element (Cu),
25% of thegroup-III element (In),and 50% ofthe group-VI element
(Se) can be found. However, a slight increase of the group-I element
makes the material p-type and a slight increase of the group-III
element makes the material n-type in electrical conduction. The
variation in electrical conduction through p
+
,p,i,n,andn
+
has
been established in 2006 for materials based on CuInSe
2
[16] and
in 2007 for materials based on CuInGaSe
2
[17] and the results are
summarised in section 3.4.3.
3.3.4
Ability in Bandgap Engineering
It is also possible to engineer the bandgap of alloy semiconductors,
such as CuInGaSe
2
. The bandgap of CuInSe
2
is
∼
1.10 eV, and
this value can be increased by adding gallium into the layers.
Electrodeposition provides a convenient way of this required
variation of gallium by changing the growth voltage. This property,
therefore, can be used for the effective absorption of a major part of
thesolarspectrumusingmulti-layergradedbandgapstructures(see
Fig. 1.16 and chapter 6). These new device structures need gradual
variation of the bandgap together with electrical conduction type
change from p-type to n-type, or vice versa. The electrodeposition
of CuInGaSe
2
simultaneously provides both these variations during
the growth process [17].
3.3.5
Other Advantages of Electrodeposition
There are many other advantages in the electrodeposition of
semiconductors. In techniques such as MBE and MOCVD, the phase
changes occur directly from gas to solid during the materials
growth process. However, in electrodeposition, phase changes
occur from liquid to solid and nature prefers this transition and,
therefore, should produce high-quality material layers. In addition,
the available source of electrons at the cathode surface should
provide better growth conditions, fulfilling the charge neutrality
requirements during materials growth.
One other important feature of electrodeposition is the possi-
bility of defect passivation in a wet chemical environment. As the
