Strained Superlattice photocathode development using CBE and MBE

Conference · Fri Sep 01 04:00:00 EDT 2023

DOI:https://doi.org/10.2172/2283317· OSTI ID:2283317

Stutzman, Marcy ^[1]; Palmstrom, Chris ^[2]; Engel, Aaron ^[2]; Blume, Gregory ^[3]

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1. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
2. University of California, San Francisco, CA (United States). Laboratory of Radiobiology and Environmental Health (LREH)
3. Old Dominion Univ., Norfolk, VA (United States)

High polarization electron beams for accelerators are generated using strained superlattice GaAs-based photocathodes. A collaboration of researchers at University of California Santa Barbara and Jefferson Lab has been investigating growth of SSL photocathodes using either chemical- or molecular-beam epitaxy (CBE or MBE) to re-establish a source of high polarization photocathode material. While calibrating growth parameters for the now standard GaAs/GaAsP strained superlattice structure, the UCSB personnel encountered the drawbacks of growing structures with phosphorus in a MBE or CBE system, including high vapor pressure byproducts, phosphorus contamination in both the GaAs layer and all subsequent materials grown in that chamber, and highly flammable and toxic chamber residues. For these reasons, the UCSB team began additionally investigating strained superlattices of InAlGaAs/AlGaAs, which has been successfully demonstrated in the literature1, to be a high QE, high polarization photocathode material. For GaAs/GaAsP, varying phosphorus content affects both the band gap and polarization. However for InAlGaAs/AlGaAs, In and Al content can be varied independently and allows optimization of both polarization and bandgap. Several variations on InAlGaAs/AlGaAs superlattice photocathodes, including those with distributed Bragg reflector (DBR) structures to enhance QE, have been grown at UCSB and sent to Jefferson Lab for testing. The initial results are quite promising, with polarization over 80% and QE about 0.3%, and ongoing test results will be presented.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 2283317
• Report Number(s): JLAB-ACC-23-3993; DOE/OR/23177-7393
• Country of Publication: United States
• Language: English