Environmental Engineering Reference
In-Depth Information
Table11.2 Experimentallyobserved defectlevels inmetalorganic vapour
phase epitaxy (MOVPE)Al
x
Ga
(1
−
x
)
As layers [4, 5]
Approximate Concentration (cm
-
3
)
Al Content (x)
Activation Energy, E
a
(eV)
0.05-0.11
0.41
10
14
-10
16
0.15
0.50
10
15
10
15
0.20
0.55
(0.00-0.25)
(0.80-0.90)
The varying EL2level according to
thevalueof x
similartothoseofCdTe-andCIGS-basedsolarcells.Itisappropriate
at this stage to refer to the well-researched and documented deep
levels in GaAs [4] and AlAs [5] materials in the literature.
There exist a large number of experimentally observed defect
levels in MOVPE-grown GaAs and AlAs materials, as summarized in
Table 11.2
These observations indicate that the Fermi-level pinning is also
affecting GaAs-based solar cells in a way very similar to those
observed for CdTe and CIGS-based solar cells. This is the main
reason for the observation of open circuit voltages grouped into
well-defined clusters.
References
1. I. M. Dharmadasa, A. P. Samantilleke, J. Young, and N. B. Chaure (2002)
Semicond. Sci. Technol.
,
17
, 1238.
2. I. M. Dharmadasa (2009)
Semicond. Sci. Technol.
,
24
, 055016-055025.
3. G.J.Bauhuis,P.Mulder,E.J.Haverkamp,andJ.J.Schermer(3-7September
2007)Proceedingsofthe22ndEuropeanPhotovoltaicConference,Milan,
Italy.
4. INSPEC(1990)
Properties of GalliumArsenide
,2ndedn,EMISDataReview
Series No. 2.
5. S. Adachi (ed) (1993)
Properties of Aluminium Gallium Arsenide
, EMIS
Data Reviews Series No. 7, London, INSPEC.
