Comparison of ALINGAAS/GAAS Superlattice Photocathodes Having Low Conduction Band Offset Page: 4 of 5
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observe a blue shift for the experimental peak. Although longer wavelength
photons in general provide more spin selectivity, they also photogenerate
electrons primarily in the BBR where there is less polarization selectivity. Also,
the electrons photogenerated in the SL structure by longer wavelengths
thermalize faster and get trapped more easily in the BBR where they depolarize.
Simulation results match the polarization peak height when depolarization is
considered to take place in the BBR (line2, figure 1).
All the Ioffe samples were protected by As caps. The highest polarization
(91%) was measured when sample #5-777 was heat cleaned at 4500C, while the
peak polarization dropped to 85% after heat cleaning at 5400C. The SVT
samples where activated after being heat cleaned at 5400C. The effect of the
heat cleaning temperature on the polarization suggests that there is a surface
factor that contributes to the depolarization. One possible explanation is that the
SVT samples have a broader BBR than sample #5-777 due to higher heat
cleaning. Samples #6-329 and #6-410 have lower doping at the surface layer
and thus, broader BBR than #5-777 and they don't achieve high polarization
As shown in the
(004) x-ray results of
Figure 3, the In
u concentration is
slightly higher in the
#5501 sample. The
. .structure of the SVTA
Figure 3. (004) X-Ray analysis of samples 5501 and 5-777. samples can
Sample 5-777 has a "cleaner" structure and slightly smaller contribute to the lower
period (5.01nm) compared to sample 5501 (5.1Onm). polarization due to
The results suggest that although the flat CB samples are promising for high
polarization, the polarization seems to depend on surface effects and structural
details that are not yet fully understood. Further studies and SIMS analysis of
the samples need to take place in order to draw final conclusions about these
1. T. Nishitani, et al., J. Apple. Phys., 97, 094907 (2005).
2. T. Maruyama et al., Appl. Phys. Lett., 85, 2640 (2004).
3. Yu. Mamaev et al., SPIN 2004, p. 913, SLAC-PUB-10891
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Ioakeimidi, K,; Maruyama, T.; Clendenin, J.E.; Brachmann, A.; Garwin, E.L.; Kirby, R.E. et al. Comparison of ALINGAAS/GAAS Superlattice Photocathodes Having Low Conduction Band Offset, article, March 31, 2006; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc876623/m1/4/: accessed June 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.