Spin dynamics of carriers in quantum wells

Britton, Robert Stanley (1999) Spin dynamics of carriers in quantum wells. University of Southampton, Doctoral Thesis.

Abstract

Carrier spin dynamics have been investigated in Type I gallium arsenide/aluminium gallium arsenide quantum well samples using a time resolved, polarisation sensitive, near normal incidence, degenerate pump-probe reflectivity technique. The effects of well width, of n-type modulation doping and of temperature from 10 to 300 K have been investigated in samples from a variety of molecular beam epitaxy laboratories.

In intrinsic quantum wells the transition from exciton to free carrier dominated spin relaxation has been investigated for the first time and occurs in the temperature interval 55-85 K in accord with theoretical predictions of exciton thermal equilibrium and dissociation rates. The electron spin relaxation rate has been measured in GaAs/AlGaAs quantum wells, which range in width from 6-20 nm, grown on the same wafer over the temperature interval 90-300 K.

Comparison with theoretical predictions based on mechanisms of spin relaxation proposed by Elliott and Yafet, Bir, Aronov and Pikus and D'yakonov and Perel show that the latter mechanism accounts for the observed magnitude and temperature and well width dependence of electron spin relaxation. At 300 K measurements on a variety of wells has shown that samples with a common origin and hence similar interface morphology and momentum scattering rate, exhibit a spin relaxation rate that varies as E_1e² as expected for the D'yakonov-Perel mechanism. The rates observed in the narrowest wells deviate from this trend, indicating an additional scattering mechanism which is attributed to the influence of interface roughness.

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