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Various light-emitting diodes of 6H-SiC, doped in the n layers with AI, Ga, or B acceptors and N donors, have been fabricated using a rotation dipping technique. A detailed study of electroluminescence mechanisms from -100 to 400 K has been carried out using photoluminescence, electroluminescence, and time-resolved spectra. At low temperatures the radiation originates mainly in the p layer, and around room temperature in the n layer. The luminescence mechanisms are free-exciton recombinations for the peak at -425 nm, donoracceptor pair recombinations for the main broad band, transitions within localized centers for the peak at -455 nm, and recombinations due to divacancies for the series of peaks beginning at -470 nm. The dependence of the electroluminescence efficiency on the N concentration in the n layers is studied and methods to improve efficiency are discussed. The maximum external quantum efficiencies obtained were 1.2 X 10-5 for AI-doped, 9 X 10-6 for Ga-doped, and 2.5 X 10-5 for B-doped diodes, and were improved by a factor of 2 by using an epoxy coating.

An experimental study of low-frequency turbulence with wavelengths ranging from 2.5 to 0.4 cm in the WT-1 Tokamak is carried out by HCN laser scattering. It is found that the higher-frequency fluctuations are contained in the inner and the lower-frequency ones in the outer part of the plasma column.

Siple station VLF wave injection experiments aimed at finding the properties of the magnetospheric hot plasma were conducted for a 9‐hour period between 1705 and 0210 UT on January 23–24, 1988. A special frequency versus time format, lasting l min and transmitted every 5 min, consisted of a sequence of pulses, frequency ramps, and parabolas, all in a 1‐kHz range centered on 2400 Hz. The transmitted signals, after propagating along a geomagnetic field‐aligned duct, were recorded at Lake Mistissini, Canada. At various times during the 9‐hour interval the Siple signals showed features characteristic of wave‐particle interactions, including wave growth, sidebands, and triggered emissions. Our observations, primarily at 2400 Hz, show that (1) there were no correlations between the initial levels, the growth rates, and the saturation levels of constant‐frequency pulses; (2) in general, the values of growth rate and saturation level of two pulses injected within 30 s were nearly the same; (3) the initial level, growth rate, and saturation level showed temporal variations over 5–15 min and 1–2 hour timescales; (4) the leading edges of constant‐frequency signals underwent spatial amplification; and (5) under conditions of saturation the received signal bandwidth (∼ 20 Hz) remained constant over a 1‐hour period, although the saturation level and growth rate varied during the same period. On the assumption that gyroresonant interactions were responsible for the observed wave growth and saturation, the timescales over which those phenomena varied provide constraints on the possible energetic electron population within the duct. In the reference frame of the duct (L ∼ 5.1, Ne ∼ 280 cm−3) the particle fluxes showed no variation over a 30‐s timescale but varied over 5–15 min and 1–2 hour timescales. The 5–15 min timescale variations indicate longitudinal structures ranging from ∼ 0.2° or ∼100 km (in the equatorial plane) for electrons with energy E = 0.6 keV and pitch angle α = 40°, to ∼ 5° or ∼2800 km for electrons with energy E = 11 keV and pitch angle α = 80°. The hour‐long time variations indicate longitudinal structures ranging from ∼ 2° or ∼1100 km (in the equatorial plane) for electrons with energy E = 0.6 keV and pitch angle α = 40°, to ∼ 45° or ∼25,000 km for electrons with energy E = 11 keV and pitch angle α = 80°. We conclude that ground‐based active and passive wave experiments have substantial potential for investigating properties of the hot plasma of the magnetosphere.

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