Optimized photocathode for spin-polarized electron sources

Abstract

Photocathode for highly polarized electron emission has been developed, fabricated, and studied. The photocathode is based on short-period strained AlInGaAs∕AlGaAs superlattice grown by molecular beam epitaxy. Deformation of AlInGaAs quantum well results in 87meV energy splitting between heavy hole and light hole minibands. Electron emission from the developed photocathode demonstrates maximal polarization of 92% with quantum efficiency of 0.85% at room temperature.

Spin polarized photoemission from strained Ge epilayers

“…[8][9][10] However, the maximum polarization in our Ge film, P =62Ϯ 3% for h = 1.26 eV, is considerably lower than what obtained in III-V based structures, where values exceeding 80% have been reported. [8][9][10] It has to be noted that in Ge, due to the above mentioned impossibility of reaching NEA conditions, the photoemission threshold does not coincide with the semiconductor ͑direct͒ gap, which is instead the standard situation in the III-V case. Thus, in Ge electrons are excited out from the ⌫ point by photons with energies considerably larger than the gap, resulting in a polarization lower than the one corresponding to band-gap excitation.…”

“…14 A polarization reduction to values around 60% is indeed observed in III-V strained films for photon energies Ϸ100 meV larger than the gap. [8][9][10] This suggests that extremely highly polarized electrons can be produced in the CB minimum at ⌫ also in strained Ge films by using resonant excitation. These electrons cannot however exit the crystal, so that their, possibly very high, spin polarization is not detectable by photoemission.…”

Improvement of Quantum Efficiency in Transmission-Type Spin-Polarized Photocathode

“…In the strained SL structure, the heavy-hole and light-hole mini-bands are split due to both the elastic strain effect and the quantum confinement effect. The reflection-type photocathodes based on a GaAs/GaAsP strained SL [11] and an AlInGaAs/AlGaAs strained SL [12] produced a high spin polarization (SP) of approximately 90%.…”

Pure spin currents in Ge probed by inverse spin-Hall effect

“…In this materials optically-injected electrons can reach spin polarization values up to 50% in bulk semiconductors [4][5][6][7][8] or even larger in semiconductor nanostructures. [8][9][10][11][12][13][14][15][16] In this respect it would be highly desirable to implement the control of the spin degree of freedom in Ge-based heterostructures, which can be integrated on the common Si-based electronics platform. In bulk Ge the energy difference between direct (E d = 0.80 eV) and indirect (E i = 0.66 eV) bandgap is only 140 meV at room temperature.…”