Randy A. Roush

Effects of pulse risetime and pulse width on the destruction of toluene and NO/sub x/ in a coaxial pulsed corona reactor

The efficient abatement of hazardous air pollutants has become a major concern for many private and military installations. The semiconductor processing industry is being scrutinized for emission of many perfluorinated compounds (PFCs) and volatile organic compounds (VOCs). A major concern in the military is the effluent from paint-spray applications. Most of the air emission from the military installations are VOCs from the paint-spray booths and associated drying booths. Also, there is interest in the destruction of oxides of nitrogen (NO/sub x/) from both stationary and mobile diesel engines. The pulsed corona reactor (PCR) is a nonthermal plasma discharge device which has been used to efficiently convert a variety of hazardous air pollutants into byproducts that can be filtered by standard technology. In this work, the authors show the effects of pulse parameters (pulsewidth and risetime) on the destruction of toluene and NO/sub x/ using a PCR.

Compensation of shallow silicon donors by deep copper acceptors in gallium arsenide

Electrical compensation in n‐type, silicon‐doped, GaAs (GaAs:Si) has been achieved for several different silicon doping densities. The introduction of deep copper acceptors into GaAs:Si through a thermal diffusion process has produced semi‐insulating GaAs:Si:Cu. The density of diffused copper is shown to be predicted, to a good approximation, by knowledge of both the annealing temperature at which compensation is observed, and the initial free‐electron density. Also, a model based on Fermi–Dirac statistics has demonstrated the same qualitative behavior as the data.

Analysis of nonohmic current‐voltage characteristics in a Cu‐compensated GaAs photoconductor

An analysis of observations of nonohmic current conduction in a copper‐compensated GaAs (GaAs:Cu) photoconductive switch is presented. It is demonstrated that conduction during illumination and at modest current densities can be attributed to an optically injected plasma influenced by single‐injection contact effects. However, at higher current densities, a double‐injection model is more suitable. We provide further evidence that the transition from a single‐injection process to a double‐injection process is accompanied by the formation of at least one current filament with cross‐sectional area of 5×10−4 cm2, and a peak current density greater than 103 A/cm2. We finish by suggesting avalanche breakdown at the n+−i anode junction as a possible mechanism for the onset of significant hole injection at the anode, a condition necessary to justify the use of a double‐injection‐dominated transport model in an essentially n‐i‐n device.

Effects of 1-MeV neutron irradiation on the operation of a bistable optically controlled semiconductor switch (BOSS)

Recent subnanosecond-opening results of the semiconductor switch (BOSS) bistable optically controlled are presented. The processes of persistent photoconductivity followed by photo-quenching have been demonstrated in copper-compensated, silicon-doped, semi-insulating gallium arsenide (GaAs:Si:Cu). These processes allow a switch to be developed that can be closed by the application of one laser pulse (/spl lambda/=1.06 /spl mu/m) and opened by the application of a second laser pulse with a wavelength equal to twice that of the first laser. The opening phase is a two-step process which relies initially on the absorption of the 2-13-/spl mu/m laser and finally on the recombination of electrons in the conduction band with holes in the valance band. The second step requires a sufficient concentration of recombination centers in the material for opening to occur in the subnanosecond regime. This report discusses the effects of 1-MeV neutron irradiation on the BOSS material for the purpose of recombination center generation. Initial experiments indicated a reduction of the recombination time from several nanoseconds down to about 250 ps. Both experimental and theoretical results are presented. >

COAXIAL PULSED CORONA REACTOR FOR TREATMENT OF HAZARDOUS GASES

Abstract : The destruction of hazardous gaseous chemicals has in the past been effectively accomplished using thermal techniques. Pulsed corona reactors are promising candidates for more efficient destruction of hazardous gases using a non-thermal electrical discharge at atmospheric pressure. The energy required for chemical destruction is deposited in the medium by highly energetic electrons present near the streamer head while direct heating of the neutral gas molecules is avoided. The current work emphasizes the construction of an electrically efficient, low cost pulsed corona reactor capable of treating a flow rate of 4 liters/minute. Determining optimum pulse parameters for the discharge and scaling the device to higher flow rates will be the primary focus of future work, with specific emphasis being placed on the use of fast-rising pulses (nanoseconds) of limited pulse-width (10s to 100s of nanoseconds). A testbed for chemical analysis has also been assembled and preliminary results include the electrical efficiency of the device and the chemical destruction efficiency when challenged by small concentrations of hazardous gases in ambient air.

Subnanosecond high-power performance of a bistable optically controlled gaas switch

Abstract : Recent subnanosecond-opening results of the Bistable Optically controlled Semiconductor Switch (BOSS) are presented. The processes of persistent photoconductivity followed by photoquenching have been demonstrated in copper-compensated, silicon-doped, semi-insulating (GaAs:Si:Cu). These processes allow a switch to be developed that can be closed by the application of one laser pulse (Iambda= 1.06 pm) and opened by the application of a second laser pulse with a wavelength equal to twice that of the first laser. The opening phase is a two-step process which relies initially on the absorption of the 2.13-(mu)m laser and finally on the recombination of electrons in the conduction band with holes in the valence band. The second step requires a sufficient concentration of recombination centers in the material for this process to occur in the subnanosecond regime. This report discusses the effects of 1-MeV neutron irradiation on the BOSS material for the purpose of recombination center generation. Initial experiments indicated a reduction of the recombination time from several nanoseconds down to about 180 ps. Both experimental and theoretical results are presented.

IMPACT OF COPPER DIFFUSION ON THE HIGH POWER SWITCHING PERFORMANCE OF Si-DOPED. Cu-COMPENSATED GALLI

The Bulk Optically Controlled Semiconductor Switch (BOSS) is based on GaAs doped with silicon and compensated with diffused copper. The BOSS device can be turned on with a laser pulse of one wavelength and turned off with a second laser pulse of a different wavelength. The resulting electrical pulse duration may be varied depending on the timing between the two, relatively short, laser pulses. This device relies on the processing of silcon-doped, copper-compensated gallium arsenide. Diffused copper forms several deep acceptor levels in GaAs:Si, with the two dominant levels labeled Cu, and Cu,, located 0.14 eV and 0.44 eV from the top of the valence band, respectively. The BOSS switching concept relies on the Cu, level; therefore the Cu, level is undesirable. Copper may also complex with native defects such as EL2, which effects the switching performance of this photoconductor by extracting from the total Cu, concentration. The goal of this research is to investigate the processing parameters in order to find an operating point that will consistently produce switches with low dark conductivities and high on-state conductivities.

Chemical destruction using a pulsed corona reactor

Chemical destruction measurements for a Blumlein driven pulsed corona reactor are presented along with observed current and voltage waveforms. The input gas flow consists of 0.2 to 1.5 SLPM room temperature air with a 200 ppm toluene impurity. The PCR is operated with an applied voltage of between 12 to 30 kV at 5 to 50 Hz repetition rate. The dependence of the PCR chemical destruction on rep-rate, applied voltage and flow are reported. Apparatus to observe the relation between the emission spectra and the chemical destruction is discussed.

Infrared photoconductivity via deep copper acceptors in silicon-doped, copper-compensated gallium arsenide photoconductive switches

Silicon-doped, copper-compensated, semi-insulated gallium arsenide of various doping parameters was studied with respect to infrared photoconductivity. This material is used as a photoconductive switch, the bistable optically controlled semiconductor switch (BOSS). One limitation was the relatively low conductivity of the device during the on-state. Typically, silicon-doped gallium arsenide is converted to semi-insulating gallium arsenide by the thermal diffusion of copper into the GaAs:Si. It is shown that variation of the diffusion parameters can improve the on-state conductivity by the enhancement of the concentration of a copper center known as Cu/sub B/. The conductivity of the device 150 ns after irradiation from a 20-ns FWHM laser pulse ( lambda =1.1 mu m) is recorded for various incident energies. This on-state conductivity saturates at a value that is predicted by the densities of the copper levels and the mobility. >

SUBNANOSECOND PERFORMANCE OF THE BOSS GaAs OPENING SWITCH

We report recent subnanosecond photoconductive measurements on a p-i-n device made from a coppercompensated semi-insulating GaAs substrate. Photoconductivity in this relatively large volume device (0.5 x 5 x 10 mm3) is generated by extrinsic absorption of a 1-pm laser pulse, and optically quenched with a 2pm laser pulse. Device risetimes on the order of 140 ps are reported along with relatively slow (-ns) fall times. It is shown that these large, high-power (multimegawatt) switches have the potential to switch subnanosecond pulses when a copper-compensated GaAs material with suitably fast electron-hole-pair recombination rate is developed.