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We examine the applicability of the Langmuir-type of characterization for atmospheric pressure plasma jets generated in a millimeter-size cavity microwave resonator at 2.45 GHz. Wide range I-V characteristics of helium, argon, nitrogen, air and oxygen are presented for different gas fluxes, distances probe-resonator, and microwave powers. A detailed analysis is performed for the fine variation in the current around the floating potential. A simplified theory specially developed for this case is presented, considering the ionic and electronic saturation currents and the floating potential. Based on this theory, we conclude that, while the charge carrier density depends on gas flow, distance to plasma source, and microwave absorbed power, the electron temperature is quite independent of these parameters. The resulting plasma parameters for helium, argon, and nitrogen are presented. [ABSTRACT FROM AUTHOR]

We examine transport and relaxation dynamics of optically excited electrons in GaAs-based heterostructure layers, involving dilute nitrides in percent-level concentration range. Such heterostructures contain materials with very different mobilities. Drift instead of Hall mobility is determined using a special technique. The value of the mobility of photogenerated electrons in a freestanding, 3% N InGaAsN layer, as part of a two-layer structure of 100 nm GaAs/2 μm nitride, is found to be of the order of 2 cm2/Vs, much lower than other values reported in the literature. The concomitant presence of carriers in the GaAs and nitride layers leads to formation of a barrier at the interface region that hinders electrons to enter in the nitride material. The dwell time of photoexcited electrons in GaAs interfacing the nitride layer is of the order of milliseconds, as seen by photoconductivity transients after pulsed optical excitation, much longer than the resulted time from optical experiments. Comparison of optical with transport properties reveals that the same centers involved in luminescence, that appear to be extended, are responsible also for hopping transport, where they appear as deep states. A theoretical explanation is given. [ABSTRACT FROM AUTHOR]

This work is a theoretical and experimental study of the time-resolved microwave spectroscopy, close to the limit ΔωΔτ∼1, especially applied for the case of cyclotron resonance. A dynamic perturbation theory of a resonator is presented. While the amplitude of a transmitted signal in a standard measuring setup can be determined quickly and accurately, the phase relation requires much longer time for the same accuracy. The use of a resonant system enhances the sensitivity for determination of amplitude and phase, but reduces the time resolution, both by a factor Q. The nonlinear regime for conductivity in cyclotron resonance conditions is compensated by the use of constant energy density in the resonator, independent of frequency. Examples for classical semiconductors are presented. Compared with terahertz time-resolved spectroscopy, this method offers precise information in a different time scale and essentially in a different experimental regime of conductivity: pulsed, E∼1 kV/cm in the first case; cw, E∼1 V/cm in ours. [ABSTRACT FROM AUTHOR]