GaAs-based superlattice photocathodes manufactured using MOCVD provide spin polarization > 90% and quantum efficiency > 1%

Conference · Wed Mar 01 04:00:00 EST 2023

DOI:https://doi.org/10.2172/2282043· OSTI ID:2282043

Poelker, Matt ^[1]

---

1. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

Spin-polarized electron beams are important for nuclear physics research performed at electron accelerators. Over many years, beam polarization has increased significantly, from 35% provided by unstrained bulk GaAs, to ~ 75% using single strained-layer GaAs, to ~ 90% using strained-superlattice GaAs photocathodes grown using molecular beam epitaxy (MBE). Commercial vendors once provided high-polarization photocathodes but today there is little interest in supporting this small market. Here, we report successful results fabricating high polarization GaAs/GaAsP superlattice photocathodes using metal organic chemical vapor deposition (MOCVD), a method dismissed by some as not providing sufficient control of layer thickness and uniformity. The best samples provide spin polarization greater than 90% and quantum efficiency (QE) exceeding 2%, with QE enhanced using a distributed Bragg reflector (DBR) incorporated into the structure. Together, these quantities represent some of the best results ever reported for high polarization photocathodes. Enhanced QE via DRB is very important for future work at CEBAF/Jefferson Lab because it will simplify the production of polarized electron beams at milliampere current needed for a polarized positron source.

• 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: 2282043
• Report Number(s): JLAB-ACC-23-3781; DOE/OR/23177-5791
• Country of Publication: United States
• Language: English