Excitons in the thallous halides

Abstract

A thin film fabrication technique resulting in a considerable reduction in strain has been developed and has facilitated the optical and magneto-optical experiments on the Thallous Halides. The strain reduction achieved has revealed optical spectra of exceptional sharpness, Previously undiscovered absorption features have appeared and exciton effects have been established. A variety of experiments were performed to clarify the nature of the structure associated with the first exciton peak. Intrinsic structure and structure due to strain lifted degeneracy has been identified. These experiments also provided criteria for evaluating the films. Analysis of the optical absorption spectra to yield the optical constants was performed and the spectra correlated with the magnetoabsorption results. Both Faraday rotation and direct magneto-absorption experiments were performed. Analysis of the experiments yielded exciton binding energies, effective reduced and carrier masses, effective g values, the energy gaps, peak positions and spin orbit splittings. A phonon sideband to the first exciton peak has been found and its character extensively investigated. The sideband is believed to arise from an exciton-longitudinal optical phonon coupled state.