MBE Growth of Graded Structures for Polarized Electron Emitters Page: 3 of 10
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The spin orbit (SO) coupling is more pronounced in superlattice structures due to
heterointerface asymmetries. A 10-15nm GaAs layer of high p- doping (5x19 cm3) at
the cathode surface is desirable in order to achieve NEA reliably. The SL structure
should have low p-doping (~1x17 cm3) in order to increase mobility and avoid
depolarization due to scattering. The increased doping at the surface results in an
elevated CB at the surface that can be compensated by the SL miniband as long as the
conduction miniband is higher that the conduction band level at the surface. The entire
structure was grown on a GaAs substrate with an AlGaAs energy barrier layer.
In principle, the A1XGa1.XAsySbi~y quaternary alloy provides design flexibility. The
percentage of Sb can be used to experiment with the effect of spin orbit coupling and
band lineup and the Al percentage can be used to control the band offsets and LH, HH
valence band splitting.
Three device structures were grown on 2" diameter GaAs substrates by molecular
beam epitaxy (MBE). The structures all utilized AlxGa1.xAso.s2Sbo.is alloy in the
superlattice, where the aluminum composition was changed between the samples
being x = 5, 10 or 15%.
X-Ray of 10% Al
315 32.0 32,5
X-ray diffraction measurement and
33.0 335 3ao simulation of AlGaAsSb/GaAs
superlattice photocathode structure.
The simulation assumes 100% strain.
31.0 31.5 32.0 32.5
j3 10A -
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MBE Growth of Graded Structures for Polarized Electron Emitters, report, August 25, 2010; [California]. (digital.library.unt.edu/ark:/67531/metadc1015059/m1/3/: accessed November 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.