Electron spin-relaxation dynamics in GaAs/AlGaAs quantum wells and InGaAs/InP quantum wells

We have investigated the spin-relaxation process of electrons at room temperature in undoped GaAs/AlGaAs multiple-quantum wells (MQWs) and InGaAs/lnP MQWs. The spin-relaxation times are measured for different well thicknesses using time-resolved spin-dependent pump and probe absorption measurement. The spin-relaxation time, tau(s), for GaAs MQWs was found to depend on the electron confinement energy, E-1e, according to tau(s) proportional to E-ie(-2.2), demonstrating that the main spin-relaxation mechanism at room temperature is the D'yakonov-Perel' process. The measured spin-relaxation times of InGaAs MQWs whose band-gap is about half that of GaAs MQWs are about 5 ps and vary depending on the quantum confinement energy EI,, according to tau(s) proportional to E-ie(-1.0). The spin-relaxation time by Elliott-Yafet process, which becomes stronger for narrower band-gap materials, is calculated for quantum wells and shown to vary according to tau(s) proportional to E-ie(-1). The spin-relaxation mechanism and possible applications using this fast spin-relaxation process are discussed.