Multisubband effect in spin dephasing in semiconductor quantum wells

The multi-subband effect on spin precession and spin dephasing in $n$-type GaAs quantum wells is studied with electron-electron and electron-phonon scattering explicitly included. The effects of temperature, well width, and applied electric field (in a hot-electron regime) on spin kinetics are thoroughly investigated. It is shown that due to the strong inter-subband scattering, the spin procession and the spin dephasing rate of electrons in different subbands are almost identical despite the large difference in the D’yakonov-Perel’ (DP) terms of different subbands. It is also shown that for quantum wells with a small well width at temperatures where only the lowest subband is occupied, the spin dephasing time increases with the temperature as well as the applied in-plane electric field until the contribution from the second subband is no longer negligible. For quantum wells with large width the spin dephasing time tends to decrease with the temperature and the electric field.

Figure 1

SDT ${\tau }_s$ vs. the background temperature $T$ without the applied electric field for two QW’s with width $a=17.8\mathrm{nm}$ (●) and 12.7 nm (◆). The solid curves are the SDT calculated with the lowest two subbands included and the dashed curves are those calculated with only the lowest subband.

Figure 2

SDT vs. the applied electric field $E$ at different temperatures and well widths: ●, $T=120\mathrm{K}$; ◆, $T=200\mathrm{K}$; solid curves, $a=17.8\mathrm{nm}$; Dashed curves, $a=12.7\mathrm{nm}$. Inset: The corresponding electron temperature $T_e$ as a function of the electric field.