Large enhancement of spin polarization observed by photoelectrons from a strained GaAs layer

doi:10.1016/0375-9601(91)90995-K

Physics Letters A

Volume 158, Issues 6–7, 9 September 1991, Pages 345-349

https://doi.org/10.1016/0375-9601(91)90995-K Get rights and content

Abstract

We have observed a large enhancement of the spin polarization of photoelectrons emitted from a 0.08 μm thick strained GaAs(001) layer grown on a GaP_xAs_1−x substrate by the MOCVD method with x=0.17. For this fraction of phosphorus, the lattice-mismatch was estimated to be ∼0.6% and the energy splitting between heavy-hole and light-hole bands at the valence band maximum to be ∼40 meV. The maximum polarization of ∼86% was observed with a quantum efficiency of ∼2 x 10⁻⁴, under the conditions that the cathode was at room temperature and the excitation photon wavelength was λ≈860 nm.

References (13)

T. Maruyama et al.
Phys. Rev. Lett.
(1991)
D.T. Pierce et al.
Phys. Rev. B
(1976)
J. Kessler
Polarized electrons
(1985)
E. ReichertC. Sinclair
T. Omori et al.
90–190/DPNU-91-121152 1
(March 1991)
H. Horinaka et al.
Japan. J. Appl. Phys.
(1988)

There are more references available in the full text version of this article.

Cited by (131)

An overview of how parity-violating electron scattering experiments are performed at CEBAF
2023, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Parity-violating electron-scattering experiments represent an important focus of the nuclear physics experimental program at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. These experiments pose significant challenges because the scattering asymmetries can be very small, of the order parts-per-million and smaller. To succeed, the properties of the electron beam such as current, position, size and energy, must be very nearly identical in the two electron-polarization spin states (parallel and anti-parallel relative to the direction of beam motion at the scattering target). This paper describes the origins of unwanted helicity-correlated beam asymmetries present on the electron beam and methods to minimize them to acceptable levels.
Measurement of electron beam polarization from unstrained GaAs via two-photon photoemission
2014, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Citation Excerpt :
The first GaAs-based polarized electron source used at an accelerator [2] provided beam polarization ~35%, with a theoretical maximum polarization limited to 50% [3,4] due to the heavy-hole, light-hole energy level degeneracy of the 2p3/2 valence band state (Fig. 1a). Significantly higher beam polarization was obtained in the 1990s by introducing an axial strain within the GaAs crystal structure [5–7] which eliminates this degeneracy (Fig. 1b). Today, beam polarization at accelerators routinely exceeds 80% using strained-superlattice GaAs/GaAsP structures [8,9]; however, these high-polarization photocathodes are thin compared to typical unstrained bulk GaAs and with respect to the photon absorption depth.
Two-photon absorption of 1560 nm light was used to generate polarized electron beams from unstrained GaAs photocathodes of varying thickness: 625 μm, 0.32 μm, and 0.18 μm. For each photocathode, the degree of spin polarization of the photoemitted beam was less than 50%, contradicting earlier predictions based on simple quantum mechanical selection rules for spherically-symmetric systems but consistent with the more sophisticated model of Bhat et al. (Phys. Rev. B 71 (2005) 035209). Polarization via two-photon absorption was the highest from the thinnest photocathode sample and comparable to that obtained via one-photon absorption (using 778 nm light), with values 40.3±1.0% and 42.6±1.0%, respectively.
Picosecond electron bunches from GaAs/GaAsP strained superlattice photocathode
2013, Ultramicroscopy
Citation Excerpt :
Therefore, high spin polarization is achieved by breaking the degeneracy between the heavy-hole and light-hole valence bands at the Γ point and by exciting electrons only from one of the bands. The degeneracy can be broken by the use of a strained GaAs layer [6,7], superlattice structures [8], and strained superlattice structures [9–11]. The mechanism for generating a spin-polarized electron beam from a superlattice or strained-superlattice photocathode is shown in Fig. 1.
GaAs/GaAsP strained superlattices are excellent candidates for use as spin-polarized electron sources. In the present study, picosecond electron bunches were successfully generated from such a superlattice photocathode. However, electron transport in the superlattice was much slower than in bulk GaAs. Transmission electron microscopy observations revealed that a small amount of variations in the uniformity of the layers was present in the superlattice. These variations lead to fluctuations in the superlattice mini-band structure and can affect electron transport. Thus, it is expected that if the periodicity of the superlattice can be improved, much faster electron bunches can be produced.
Record quantum efficiency from strain compensated superlattice GaAs/GaAsP photocathode for spin polarized electron source
2023, AIP Advances
Temporal resolution in transmission electron microscopy using a photoemission electron source
2023, Microscopy
Photocathodes
2023, Handbook Of Accelerator Physics And Engineering: Third Edition

View all citing articles on Scopus

¹: Present address: Physikalisches Institut der Universität Bonn, Bonn, Germany.

View full text

Large enhancement of spin polarization observed by photoelectrons from a strained GaAs layer

Abstract

Phys. Rev. Lett.

Phys. Rev. B

Polarized electrons

90–190/DPNU-91-121152 1

Japan. J. Appl. Phys.