Electron and nuclear spin dynamics in fluorine-doped ZnSe epilayers

Abstract

Electron spins in semiconductors are considered as candidates for quantum bits. This thesis presents a study of the spin dynamics of the strongly localized donor-bound electrons in fluorine-doped ZnSe epilayers via pump-probe Kerr rotation technique. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time (T1). The excitation of the same samples with helicity-modulated laser pulses results in a transverse nuclear spin polarization, which was detected as a change of the Larmor precession frequency of the donor-bound electron spins in a magnetic field applied in the Voigt geometry. A mechanism of optically induced nuclear spin polarization is suggested based on the concept of resonant nuclear spin cooling driven by the inhomogeneous Knight field of the donor-bound electron. The all-optical induction and detection of the nuclear spin polarization allow us to measure the T1 time of the selenium-77 isotope. We combine the optical technique with radio frequency methods to measure the inhomogeneous spin dephasing time and the coherence time T2 of the selenium-77 isotope. While the T1 time is on the order of several milliseconds, the T2 time is several hundred microseconds. This verifies the validity of the classical model of nuclear spin cooling describing the optically induced nuclear spin polarization.