Strained Superlattice Ga As Be doping cm 3

Strained Superlattice Ga. As Be doping (cm -3 ) 19 Ga. As (5 nm) 5. 10 17 Ga. As. P (3 nm) Ga. As (4 nm) 18 Ga. As 0. 64 P 0. 36 (2. 5 μm) 5. 10 14 pairs Ga. As 1 -x P x , 0<x<0. 36 (2. 5 μm) p-type Ga. As 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

QE (%) 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

Polarization (%) Higher Beam polarization Measurements at Test Cave as high as 85% Recent injector measurement 82% Wavelength for Good QE and Polarization Wavelength (nm) Thomas Jefferson National Accelerator Facility Operated by the Southeastern Universities Research Association for the U. S. Depart. Of Energy Typical polarization from traditional material ~75%

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) Thomas Jefferson National Accelerator Facility Operated by the Southeastern Universities Research Association for the U. S. Depart. Of Energy This means; Smaller inherent intensity and position asymmetries on beam.

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 Accelerator Facility Hydrogen exposure time (min) 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