Epitaxially stabilized AgGaSe 2 for high-efficiency spin-polarized electron source

Abstract

High-quality spin-polarized electron source (SPES) is of fundamental importance in the investigation of spin-dependent phenomena. Generally speaking, an ideal material for SPES application should have both large spin–orbit and positive crystal-field splitting. Currently, almost all sources in use with accelerators are based on photoemission from GaAs and related materials such as strained GaAs grown on GaAsP or InGaAs grown on GaAs. Nevertheless, the reduced critical layer thickness of these strained films leads to poor material quality and, consequently, low quantum efficiency. Besides other ordered ternary semiconductor compounds, tetragonal chalcopyrite ternary compounds have also been considered. However, since all these compounds have zero or negative crystal-field splitting, the achieved polarization and quantum efficiency are rather low. Here we propose a new material, AgGaSe 2 in the CuAu phase, as a high-quality SPES. We show that it is possible to grow epitaxially strain-free AgGaSe 2 in the CuAu phase on ZnSe substrate. Since this material has a direct-band gap, a large spin–orbit splitting, as well as a large positive crystal-field splitting, it is predicted to be a promising material for SPES with 100% spin polarization.