Spin Relaxation and Lifetime in Fe/GaAs Heterostructures at Low Temperatures

Abstract

In the research reported in this thesis, the spin properties of an Fe/n-GaAs lateral spin valve were studied. Of special interest in the study of spin dynamics in semiconductors is determining sources of spin relaxation at low temperatures and distinguishing their range. The goal of this paper is to extend current knowledge of electron spin relaxation and lifetime τs at sub-40 K temperatures in Fe/n-GaAs spin valves, employing a pump-probe measurement scheme to remove hyperfine effects. Chapter 1 begins with an overview of the study of τs in n-GaAs. The relevant spin relaxation mechanisms at low temperatures are laid out as well as the spin transport theory. Chapter 2 describes the charge transport properties of the sample studied and the standard measurement techniques to be used in this paper. In Chapter 3, spin valve results and Hanle data are examined to determine τs and diffusion coefficients. Diffusion coefficients are determined using the standard 1D lateral spin drift-diffusion model as well as transport measurements. Chapter 4 looks at the temperature dependence of the τs and compares results to published work. In particular, τs values obtained from 1-parameter and 2-parameter fitting of Hanle data are in agreement and indicate τs continues to increase below T = 20 K. Current pulsing is also shown to remove any visible Dynamic Nuclear Polarization (DNP) signatures down to T = 2 K. The spin relaxation rate below 40 K is not found to be consistent with D’yakonov-Perel’ or Elliot-Yafet relaxation. Furthermore, differences in τs values between similarly doped n-GaAs spin valves are observed and could be explained by complications inherent to the τs measurement schemes.