Gallium Arsenide Photoconductive Switches Research Articles

Focus on lasers, imaging, microscopy, and nanoscience

Focus on lasers, imaging, microscopy, and nanoscience

Experimental Research on Inhibition of Surface Flashover Based on High Power Gallium Arsenide Photoconductive Switches Triggered by Laser

Semi-insulating gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) have great potential for high voltage switching application, however, the utility is restricted by surface flashover which would result in breakdown. In this paper, a model of photo-activated charge wave was proposed based on the theory of photo-activated charge domain (PACD) in GaAs PCSS, and moderate suppression of PACD formation by loading the semiconductor surface with dielectric material was investigated theoretically and experimentally. Current as high as 3.7 kA was obtained at 28 kV, implying that this method can effectively inhibit the surface flashover and improve the service life of DC charged GaAs PCSS.

Effects of Field-Dependent Trapping and Detrapping on the Responses of Compensated GaAs Photoconductive Switches

In this paper, the response of a semi-insulating gallium arsenide photoconductive switch used in high-power microwave generation has been analyzed through experiment and simulation. The switch characteristics as a result of trapping and detrapping phenomena during a transient are studied. Analysis show that field-enhanced capture at high field locations during the onstate creates a temporary reservoir of trapped charge at different pockets in the device. Release of trapped charge and the subsequent injection of carriers from the contacts to maintain charge neutrality helps maintain conduction, which persists even after the laser pulse until all charges are transferred across the device. A model has been presented which can explain such phenomena as lock-on effect, persistent conductivity, and low-power requirement during transients. This phenomenon is unique to semi-insulating gallium arsenide and is primarily due to field-enhanced trapping and could be applicable to other materials that have similar characteristics

Monopole Charge Domain in High-Gain Gallium ArsenidePhotoconductive Switches

Considering that semi-insulating galliumarsenide photoconductive switches can be triggered into the high gainmode and no reliable theories can account for the observed transientcharacteristics, we propose the monopole charge domain model to explainthe peculiar switching phenomena occurring in the high gain mode and wediscuss the requirements for the lock-on switching. During operation onthis mode, the applied field across the switch and the lock-on fieldare all larger than the Gunn threshold field. Our developed monopolecharge domain is based on the transferred-electron effect, but thedomain is only composed of large numbers of electrons piled up due tothe negative differential mobility. Using the model and taking thephysical mechanism of the avalanche impact ionization and recombinationradiation into consideration, we interpret the typical phenomena ofthe lock-on effect, such as the time delay between the beginning of opticalillumination and turning-on of the switch, and the conduction mechanism of thesustaining phase. Under different conditions of bias field intensityand incident light energy, the time delay of the switching iscalculated. The results show that the physical mechanisms of impactionization and recombination radiation occurring in the monopole chargedomain are responsible for the lock-on switching.

Two photon absorption in semi-insulating gallium arsenide photoconductive switch irradiated by a picosecond infrared laser

We study gallium arsenide (GaAs) high voltage photoconductive switches triggered by a 30 ps neodymium: yttrium aluminium garnet (Nd:YAG) laser, i.e. using photons of energy smaller than the band gap. We measure optical absorption at Brewster incidence under optical pulse excitation and determine the extrinsic one photon and intrinsic two photon absorption coefficients. Analyzing the photoconductive resistance under different power densities of laser radiation, and using the absorption data, we demonstrate that only about 20% of the photons absorbed by the extrinsic process are converted into free electrons. We conclude that high efficiencies can only be obtained by using two photon absorption, which is feasible with ultrafast lasers and focussed beams.

Analysis of high voltage operation of gallium arsenide photoconductive switches used in high power applications

An opposed-contact photoconductive semiconductor switch, with a n+ region next to the cathode electrode has been simulated. Physical conditions during the pulse charging state, prior to high power switching, are analyzed in order to explain the increased hold-off characteristic of such devices. Results show that the introduction of the n+ region near the cathode inhibits the flow of electrons at the n+/semi-insulating interface until very high fields are reached. The formation of trap-filled regions near the contacts and the resultant inhomogeneous device characteristics that lead to breakdown are thereby shifted to higher voltages. Thus, for switches with a n+ region next to the cathode, the breakdown voltage due to unstable filamentary conduction is also increased beyond those achieved previously, allowing for higher power operation.

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling GaAs high-voltage, subnanosecond photoconductive switches in one spatial dimension

Subnanosecond high-voltage gallium arsenide photoconductive switches are studied to understand how to improve their switching speed, efficiency, and durability. Two possible mechanisms for such switching are discussed: field-compression-induced ionization of valence states and field-dependent trapping of charge carriers. Analysis and computations suggest that field compression is limited to roughly a factor of two at low initial fields. This shows that one cannot achieve arbitrary amounts of field enhancement and so obtain avalanche-like performance at will. At initial field strengths of 10 to 50 kV/cm, Gunn instabilities produce large field compression, but carrier trapping and recombination quench intrinsic photoavalanching, according to the calculations presented. Observed avalanching may therefore be due to extrinsic effects related to deep levels. As an alternative to intrinsic impact ionization, it is shown that field-dependent trap filling can yield an avalanche-like rise in current and may account for two other experimental observations, the existence of a voltage threshold and a voltage-dependent delay between the start of illumination and the occurrence of switching.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>