Spatially resolved characterization of optical loss dynamics in seminconductor bulk- and metastructures

THIS work presents new insights into optical loss dynamics in semiconductor
bulk- and metastructures. To this end, a widely applicable modeling scheme for
the calculation of photoinduced charge carrier and heat dynamics in arbitrarily
shaped semiconductor structures is developed. Analytical solutions of the
underlying equations are found for special, though practically widely applied
geometries, enabling an efficient calculation of charge carrier concentration and
temperature fields. Such a solution is used for the investigation of self-heating in
optical microring resonators for temperature sensing, pointing out the
importance of two-photon absorption effects even at moderate excitation powers[1]. Furthermore, the rigorous modeling scheme is utilized to identify key signal
contributions in photothermal deflection spectroscopy (PDS) [2], a widely applied
tool for spatially resolved absorption measurements [3,4,5]. It turns out that
nonlinear absorption and angular deflection effects occur in a variety of
experimental configurations [6]. These secondary effects must be handled
carefully for a quantitative determination of absorption parameters. In particular,
absorption coefficients close to interfaces turn out to get overestimated when
angular effects are not separated [7]. A general guideline for the reliable
determination of optical loss parameters is presented, accounting for all signal
influences. That guideline is supported by PDS measurements in crystalline
silicon. Finally, a new approach for the spatially resolved separation of various
absorption mechanisms is introduced, combining intensity dependent PDS with
dynamical optical loss modeling [8]. That approach is applied on silicon, gallium
arsenide and cadmium telluride (CdTe), reproducing previously measured twophoton absorption coefficients and determining the strength of the Franz-Keldysh
effect in polycrystalline CdTe for the first time.