High-speed measurements of solid state plasma excitation and recombination processes using microwave and laser radiation

摘要

Abstract: Ultra-fast processes of recombination of free charge carriers optically generated in natural and chemical vapor deposited (CVD) diamond materials; GaAs and Si, were investigated with a 1 nanosecond time resolution by applying a developed microwave-radiation-based technique. Time- dependent responses of reflection and transmission of 2 mm wavelength electromagnetic CW-radiation were recorded when the tested specimens were irradiated by single laser pulses of IR, visible and UV spectral range. A waveguide configuration was used to measure the exponential fall of the reflection/transmission signals corresponding to the recombination times of free carriers. Depending on the material, impurity contamination and laser wavelength, the measured signals were varied from a few to several hundred nanoseconds. The measured recombination times in the bulk of natural and CVD diamond specimens were found to be of 2-4 ns. The distinguished difference between the surface and bulk recombination times was clearly demonstrate in the case of GaAs and Si. Applicability and relevance of the applied technique to non-equilibrium carrier lifetimes measurements and the validity of the result obtained are discussed and confirmed on the base of the analytical analysis of the time-dependent microwave radiation reflection/transmission in a solid excited with high intense laser pulses. !8