David C. Stoudt

Investigation Of A Laser-controlled, Copper-doped GaAs Closing And Opening Switch For Pulsed Power Applications

This paper describes the recent power scaling of the Bulk Optically Controlled Semiconductor Switch (BOSS). The processes of persistent photoconductivity followed by photo-quenching have been demonstrated in copper-compensated, silicon-doped, semi-insulating GaAs (GaAs:Cu:Si). These processes allow a switch to be developed which can be closed by the application of one laser pulse and opened by the application of a second laser pulse of longer wavelength. The high-power switching results indicate that the BOSS device will operate at multi-megawatt power levels. The results of our power scaling effort have suggested improvements to the basic BOSS design that will allow us to achieve reliable operation at high power levels.

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.

Demonstration of a frequency-agile RF source configuration using bistable optically controlled semiconductor switches (BOSS)

The processes of persistent photoconductivity followed by photo-quenching have been demonstrated at megawatt power levels in copper-compensated, silicon-doped, semi-insulating gallium arsenide. 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 (/spl lambda/=2.13 /spl mu/m). The opening phase requires a sufficient concentration of recombination centers (RC) in the material for opening to occur in the subnanosecond regime. These RCs are generated in the bulk GaAs material by fast-neutron irradiation (/spl sim/1-MeV). Neutron-irradiated bistable optically controlled semiconductor switch (BOSS) devices have been opened against a rising average electric field of about 36 kV/cm (18 kV) in a time less than one nanosecond while operating at a repetition rate, within a two-pulse burst, of about 1 GHz. The ability to modify the frequency content of the electrical pulses, by varying the time separation, is demonstrated. Results demonstrating the operation of BOSS devices in a frequency-agile RF source configuration are also discussed.

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. >

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.

Testing and Evaluation of an Ultra-Wideband Pulse Generator for HPM Weapon Simulation

The potential for high power microwave (HPM) and radio frequency weapons (RFW) to degrade or destroy electronics has been studied for decades. However, the fast pace of change in the underlying digital technologies of modern electronics makes it necessary to continually re-evaluate the susceptibilities of such systems. The Directed Energy Technology Office has developed a major test complex at the Naval Surface Warfare Center- Dahlgren Division (NSWCDD) to study the effectiveness of a variety of HPM and RFW prototypes. The facility consists of two concrete block buildings populated with a variety of modern commercial infrastructure electronics. In this paper we discuss a recent project which typifies the testing activities at the NSWCDD facility. Schriner Engineering, Inc. built a pulse generator, the S-30, to simulate an ultra-wideband RF weapon. The S- 30 operates from AC mains and uses a series of AC and pulsed transformers to charge a wide-band antenna structure up to 100s of kV. The S-30 radiates a fast risetime short pulse (<3 ns) when an oil-filled spark gap switch closes. We report our evaluation of the S-30 design and operation, measurements of the radiated output, and modeling of the antenna pattern. We also describe the electronic systems which were tested for susceptibility to the S-30 and the test protocol that was followed.

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.

Modification of an EMP Facility to Support Threshold Testing of Electronic Systems

The naval ordnance transient electromagnetic simulator (NOTES) is a bounded wave test facility located at the Naval Surface Warfare Center, Dahlgren Division (NSWCDD). NOTES was designed to enable standardized electromagnetic pulse (EMP) testing, but in order to support tests to assess the vulnerability of US infrastructure to High-altitude EMP (HEMP) it was modified to enable threshold testing with peak amplitudes of 1 kV/m up to 100 kV/m while maintaining nominally the same temporal characteristics of the threat waveform. The range of amplitude was accomplished using three different voltage pulser configurations which provided nearly continuous variability. This paper provides a detailed description of the NOTES facility and the design, implementation, and results of these modifications. We present the waveforms that were used during testing and show that they provided a consistent stimulus both in terms of the overall waveform shape and in the critical risetime characteristic.

Bistable optically controlled semiconductor switches in a frequency-agile RF source

The processes of persistent photoconductivity followed by photoquenching have been demonstrated at megawatt power levels in copper-compensated, silicon-doped, semi-insulating gallium arsenide. These processes allow a photoconductive 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 (/spl lambda/=2.13 /spl mu/m). This switch is called the bistable optically controlled semiconductor switch (BOSS). The opening phase of the BOSS requires a sufficient concentration of recombination centers (RC) in the material for opening to occur in the subnanosecond regime. These RCs are generated in the bulk GaAs material by fast-neutron irradiation (/spl sim/1 MeV). Neutron-irradiated BOSS devices have been opened against a rising average electric field of about 36 kV/cm (18 kV) in a time less than 1 ns while operating at a repetition rate, within a two-pulse burst, of about 1 GHz. The ability to modify the frequency content of the electrical pulses, by varying the time separation, is demonstrated. Results demonstrating the operation of two BOSS devices imbedded in a frequency-agile RF source configuration are also discussed.