Transcript Strained Superlattice GaAs Be doping (cm -3 ) GaAs (5 nm) 5.10 GaAsP (3 nm) 14 pairs GaAs (4 nm) GaAs 0.64 P0.36 (2.5 μm) 5.10 5.10 GaAs 1-x P x.

Strained Superlattice GaAs
Be doping (cm -3 )
19
GaAs (5 nm)
5.10
GaAsP (3 nm)
14 pairs
GaAs (4
nm)
GaAs 0.64 P0.36 (2.5 μm)
17
5.10
18
5.10
GaAs 1-x P x , 0<x<0.36 (2.5 μm)
p-type GaAs substrate
SVT associates, per SLAC specs.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Higher Quantum Efficiency
QE ~ 1% versus 0.2%
from “traditional”
strained layer material
we operate
here
Wavelength (nm)
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Higher Beam polarization
Measurements at
Test Cave as high
as 85%
Recent injector
measurement 82%
Wavelength for Good
QE and Polarization
Wavelength (nm)
Typical polarization
from traditional
material ~75%
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Analyzing power (%)
Analyzing power (ie: QE anisotropy)
Analyzing power
smaller by factor
of 3 compared
with strainedlayer material;
4% versus 12%.
Wavlength for good QE
and polarization
Wavelength (nm)
This means;
Smaller inherent
intensity and
position
asymmetries on
beam.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
QE (%)
QE vs hydrogen cleaning
Typical H-dose to clean
anodized samples
Drawback;
Delicate material
Can’t clean with
atomic hydrogen
Makes it tough to
anodize edge of
cathode
Try arsenic
capped samples
(on order)
Thomas
Jefferson National
Hydrogen
exposure
timeAccelerator
(min) Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Superlattice vs strained layer
Pros:
• Polarization higher than strained layer
P ~ 80%
• QE is 5 times higher
QE ~ 1%
• Analyzing power smaller
A.P. ~ 3%
Cons:
• Material difficult to clean once it gets “dirty”.
• Makes it tough to anodize edge of sample.
• Suffer shorter operating lifetime. ?
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy