Environmental Engineering Reference
In-Depth Information
productionofelectronicmaterialswithenhanceddefectpassivation
using wet chemical methods rather than dry vacuum techniques.
Similar observations have been made for electrodeposited CdTe
layersusingthedeep-leveltransientspectroscopy(DLTS)technique
[19]. When electrodeposition conditions are optimised, the number
of DLTS peaks observed is minimum when compared to CdTe
materials grown by other techniques.
3.4.6
Impurity Control in Semiconductors
A comprehensive study carried out on impurities in CdTe by Lyons
et al.
[20] also provides experimental evidence for high purity of
electrodeposited CdTe layers. This group obtained CdTe from all
possible growth techniques and carried out secondary ion mass
spectroscopy (SIMS) profiling studies under similar conditions
to investigate the impurities present in these materials. This
work concluded by stating, 'Electrodeposition of CdTe has shown
polycrystalline layers which were purer than the ultra-pure crystals
bought as 4N, 5N or 5N
+
materials from various commercial
suppliers.'
This fact is also confirmed by fully processed CdS/CdTe solar
celldevicesproducedwithelectrodepositedCdTematerial.Forsolar
celldevicesshowinge
cienciesabove12%,thereversebreakdown
voltage goes up to
∼
32 V [21]. It is remarkable to observe these
∼
results for a
2
μ
m thick device structure, and these properties
highlight the purity of CdTe material in these devices showing a
large resistance to the reverse-bias breakdown process. An impure
material will produce diodes with breakdown voltages at few volts
in the reverse-bias region.
Thisexperimentalevidencedemonstratesthatelectrodeposition
with self-purification capability is producing high electronic quality
CdTe materials. With optimised growth conditions, this method is
capable of growing many other semiconducting materials.
3.5 Issues in Electrodeposition of Semiconductors
Electrodepositionfromaqueoussolutionslimitsthegrowthtemper-
atures to a narrow range of 20-85
◦
Cduetothe100
◦
C boiling point
