Enhanced spin lifetime in semiconductors with applied electric fields

The GaAsP/GaAs superlattice (SL) structure has been widely recognized as the most efficient spin polarized electron source with 90% maximum polarization and more than 1% quantum efficiency. The main spin depolarization mechanisms in these structures are: interband absorption smearing due to band-edge fluctuations, hole scattering between the heavy hole (HH) and light hole (LH) states that causes a broadening of the LH band, spin precession due to an effective magnetic field generated by the lack of crystal inversion symmetry and spin orbit coupling.

The GaAsP/GaAs superlattice (SL) structure has been widely recognized as the most efficient spin polarized electron source with 90% maximum polarization and more than 1%quantum efficiency [1]. The main spin depolarization mechanisms in these structures are: interband absorption smearing due to band-edge fluctuations, hole scattering between the heavy hole (HH) and light hole (LH) states that causes a broadening of the LH band, spin precession due to an effective magnetic field generated by the lack of crystal inversion symmetry and spin orbit coupling i.e. the Dyakonov-Perel mechanism (DP) and electron-hole scattering. The last 2 mechanisms are material related and they take place during the transport of electrons in the photocathode active region. By decreasing the transport time of the electrons in the 100nm cathode active region, all depolarization mechanisms are suppressed and the total number of scattering events also decreases. Based on the scattering rates in GaAs as a function of energy, it is possible to minimize the total number of scattering events when electrons have energies in the 0.05–0.1eVregion. Electrons can acquire such energies inside the active region during the presence of accelerating fields of . For such fields, the cathode area can be completely depleted when the doping concentration of the the active region is .