Spin phenomena in asymmetrical [0 0 1] GaAs/Alx Ga1−x As quantum wells

Abstract

Averkiev et al (2006 Phys. Rev. B 74 033305) studied carrier-spin phenomena in asymmetrical [0 0 1] GaAs/Alx Ga1−x As quantum wells by means of Hanle effect, i.e. with a magnetic field applied perpendicular to the growth direction. They interpreted their photoluminescence results with the help of a model that takes into account neither the full symmetry of carrier eigenstates nor the effect of the applied magnetic field and derived spin-relaxation times for the full photogenerated carrier population. Using the exact symmetry of carrier states, it is shown here that the magnetic field, even with a low strength, switches spin polarization of photocreated carriers along itself, whereas initial polarization is oriented along the growth direction. Switching time decreases with increasing magnetic field strength. The relevant parameter to describe spin phenomena under the field is therefore spin-switching time (whose ratio to radiative recombination time is provided versus magnetic field strength) and not spin-relaxation time. In addition, time-inversion invariance of the full carrier population under the field shows that its spin value vanishes at any time, making doubtful the concept of spin-relaxation time for the full carrier population. When no field is applied, the only meaningful spin-relaxation time is related to the growth axis. Its ratio value to radiative recombination time is 0.39. The above results demonstrate the importance of dealing with carrier wavefunctions having exact symmetry.