Spin Relaxation in GaAs/AlGaAs Coupled Quantum Wells

Spin relaxation times of electrons spatially separated from holes were evaluated by polarization and time resolved pump and probe reflection measurements. A coupled quantum well (CQW) with a structure in which two quantum wells with a width of 10 nm and 15 nm are separated by 11 nm barrier layers were used to separate electrons and holes spatially. We found that the spin relaxation time was longer in CQW compared to that of isolated well. This was attributed to the fact that the CQW had a thin (11 nm) barrier layer between the 10 nm and 15 nm wells in width, so that electrons excited in the 10 nm well tunnel into the 15 nm well, but holes do not tunnel because of their large effective mass. In other words, the electron-hole exchange interaction is weakened because the electrons and holes can be spatially separated. Suppression of the electron spin relaxation by separating electrons from holes spatially is clearly demonstrated. These results are important to control the electron spin state in semiconductor nano structure.