1. Strained Superlattice GaAs
Be doping (cm ) -3
GaAs P
1-x x
, 0<x<0.36 (2.5 μm)
p-type GaAs substrate
GaAs (5 nm)
GaAs (4 nm)
GaAsP (3 nm)
GaAs P
0.64
0.36
(2.5 μm)
14 pairs
5.10 19 17 18
SVT associates, per SLAC specs.

2. Higher Quantum Efficiency
QE (%)
QE ~ 1% versus 0.2% from “traditional” strained layer material
we operate
here
Wavelength (nm)

3. Higher Beam polarization
Measurements at Test Cave as high as 85%
Recent injector measurement 82%
Typical polarization from traditional material ~75%
Polarization (%)
Wavelength for Good QE and Polarization
Wavelength (nm)

4. Analyzing power (ie: QE anisotropy)
Analyzing power smaller by factor of 3 compared with strained-layer material;
4% versus 12%.
This means; Smaller inherent intensity and position asymmetries on beam.
Analyzing power (%)
Wavlength for good QE and polarization
Wavelength (nm)

5. 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)
QE (%)
Hydrogen exposure time (min)

6. Superlattice vs strained layer
Polarization higher than strained layer P ~ 80%
QE is 5 times higher QE ~ 1%
Analyzing power smaller A.P. ~ 3%
Material difficult to clean once it gets “dirty”.
Makes it tough to anodize edge of sample.
Suffer shorter operating lifetime. ?
Pros:
Cons: