Abstract. The spatial dynamics of the optical emission from an array of 50 times 50 individual micro cavity plasma devices are investigated. The array is operated in argon and argon-neon mixtures close to atmospheric pressure with an AC voltage. The optical emission is analysed with phase and space resolution. It has been found that the emission is not continuous over the entire AC period, but occurs once per half period. Each of the observed emission phases shows a self-pulsing of the discharge, with several bursts of emission of fixed width and repetition rate. The number of emission bursts depends on applied voltage and frequency. Spatially resolved measurements prove that the emission bursts are formed by overlapping emission pulses from single discharge cavities. Intensity differences between positive and negative half-wave can be interpreted through spatially resolved measurements of single discharge cavities.
Coupling electron-hole (e − -h + ) and electron-ion plasmas across a narrow potential barrier with a strong electric field provides an interface between the two plasma genres and a pathway to electronic and photonic device functionality. The magnitude of the electric field present in the sheath of a low temperature, nonequilibrium microplasma is sufficient to influence the band structure of a semiconductor region in immediate proximity to the solid-gas phase interface. Optoelectronic devices demonstrated by leveraging this interaction are described here. A hybrid microplasma/semiconductor photodetector, having a Si cathode in the form of an inverted square pyramid encompassing a neon microplasma, exhibits a photosensitivity in the ∼ 420 -1100 nm region as high as 3.5 A/W. Direct tunneling of electrons into the collector and the Auger neutralization of ions arriving at the Si surface appear to be facilitated by an n-type inversion layer at the cathode surface resulting from bandbending by the microplasma sheath electric field. Recently, an npn plasma bipolar junction transistor (PBJT), in which a low temperature plasma serves as the collector in an otherwise Si device, has also been demonstrated. Having a measured small signal current gain h fe as large as 10, this phototransistor is capable of modulating and extinguishing the collector plasma with emitter-base bias voltages < 1 V. Electrons injected into the base when the emitter-base junction is forward-biased serve primarily to replace conduction band electrons lost to the collector plasma by secondary emission and ion-enhanced field emission in which ions arriving at the base-collector junction deform the electrostatic potential near the base surface, narrowing the potential barrier and thereby facilitating the tunneling of electrons into the collector. Of greatest significance, therefore, are the implications of active, plasma/solid state interfaces as a new frontier for plasma science. Specifically, the PBJT provides the first opportunity to control the electronic properties of a material at the boundary of, and interacting with, a plasma. By specifying the relative number densities of free (conduction band) and bound (valence band) electrons at the base-collector interface, the PBJT's emitter-base junction is able to dictate the rates of secondary electron emission (including Auger neutralization) at the semiconductor-plasma interface, thereby offering the ability to vary at will the effective secondary electron emission coefficient for the base surface.
Coupling e−–h+ and gas phase plasmas with a strong electric field across a potential barrier yields a transistor providing photosensitivity and voltage gain but also a light-emitting collector whose radiative output can be switched and modulated. This optoelectronic device relies on the correspondence between the properties of a low temperature, nonequilibrium plasma and those for the e−–h+ plasma in an n-type semiconductor. Hysteresis observed in the collector current-base current characteristics is attributed primarily to charge stored in the base, and the photogeneration of e−–h+ pairs at the base-collector junction. Extinguishing the collector plasma requires an emitter-base junction reverse bias of <1 V.
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