A comprehensive evaluation of factors that influence the spin polarization of electrons emitted from bulk GaAs photocathodes

Abstract

The degree of polarization of photoemitted electrons extracted from bulk unstrained GaAs photocathodes is usually considerably less than the theoretical maximum value of 50%, as a result of depolarization mechanisms that originate within the photocathode material and at the vacuum surface interface. This paper provides a comprehensive review of depolarization mechanisms and presents a systematic experimental evaluation of polarization sensitivities to temperature, dopant density, quantum efficiency and crystal orientation. The highest measured polarization was ~ 50%, consistent with the maximum theoretical value, obtained from a photocathode sample with relatively low dopant concentration and cooled to 77 K. In general, measurements indicate electron spin polarization can be enhanced at the expense of photoelectron yield (or quantum efficiency, QE). I.

Monte Carlo modeling of spin-polarized photoemission from p-doped bulk GaAs

“…In this section we compare our results with available experimental data. 6,56 Assuming that the photoemission can be described by the Poisson statistics, the statistical error we should expect is the square root of the measured quantity (i.e. if the number of emitted electrons is N , the statistical error is simply √ N ).…”

“…Using the electron affinity level determined for the sample with p = 1 × 10 19 cm −3 , the QE and ESP are calculated for different doping densities and are compared to the experimental data 6 in Fig. 19.…”

“…lead to spin depolarization, and vice versa. 3,6,7 Therefore, the availability of effective modeling tools which can be used to enhance our understanding of processes which affect the performance of conventional spin-polarized electron a) E-mail address: chubenko@asu.edu sources and identify novel candidates with potentially improved capabilities is of utmost importance. Such tools are essential to design advanced photocathodes and define operational conditions that can deliver stringent demands of high spin polarization and high beam currents simultaneously as required by various applications.…”

“…. The calculated (a) QE and (b) ESP as a function of the photoexcitation energy for different electron affinity levels compared to the experimental data6,56 obtained from the sample with p = 1 × 10 19 cm −3 activated with O2 and NF3.…”

Long lifetime polarized electron beam production from negative electron affinity GaAs activated with Sb-Cs-O: Trade-offs between efficiency, spin polarization, and lifetime

“…Hot carriers that have been injected from GaAs across the heterojunction barrier have transition times in the Cs 3 Sb on the order of a few tens of femtoseconds. On such short timescales, electron spin depolarization occurring through the D'yakonov-Perel and Bir-Aronov-Pikus mechanisms is negligible [32].…”