Effects of asymmetry on electron spin dynamics in gallium arsenide quantum wells

Abstract

This work presents optical studies of electron spin dynamics in gallium arsenide (GaAs) quantum wells, focusing on the effect of inversion asymmetric confinement potentials on spin lifetimes in quantum wells grown on (110)-oriented substrates. Inversion asymmetry in the presence of the spin orbit interaction offers the possibility of complete control of electron spin dynamics in GaAs quantum wells. Symmetry arguments predict any inversion asymmetric two dimensional potential will reduce spin lifetimes via the Dyakonov-Perel spin relaxation mechanism. One aim of this work has been to make a comparison of the effect produced by an electric field to that from alloy engineering.
The suppression of the Dyakonov-Perel spin relaxation mechanism in (110) quantum wells makes them ideal candidates for measuring increases in spin relaxation due to asymmetry. To measure temporal spin dynamics, the time-resolved Kerr rotation technique was adapted in order to compensate for reduced rotational symmetry in the (110) crystallographic direction. An investigation into the effect of a transverse electric field on electron spin lifetimes was conducted. By combining spin lifetime with electron scattering time measurements it was possible to provide the first direct measurement of the Rashba coefficient. There is good agreement with k.p theory at low temperatures; however there is an unexplained increase with temperature.
Spin dynamics measurements were carried out on quantum wells with asymmetric alloy composition. Through the combination of electron spin lifetime and electron scattering time measurements it was shown that the effect of alloy engineering on electron spin dynamics is very small. This is consistent with theoretical predictions and highlights the importance of considering both conduction and valence band potentials for the understanding of the effect of asymmetry on electron spin dynamics in quantum wells.

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