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A system is presented that is capable of measuring subnanosecond reverse recovery times of diodes in wide-bandgap materials over a wide range of forward biases (0 - 1 A) and reverse voltages (0 - 10 kV). The system utilizes the step recovery technique and comprises a cable pulser based on a silicon (Si) Photoconductive Semiconductor Switch (PCSS) triggered with an Ultrashort Pulse Laser, a pulse charging circuit, a diode biasing circuit, and resistive and capacitive voltage monitors. The PCSS-based cable pulser transmits a 130 ps rise time pulse down a transmission line to a capacitively coupled diode, which acts as the terminating element of the transmission line. The temporal nature of the pulse reflected by the diode provides the reverse recovery characteristics of the diode, measured with a high bandwidth capacitive probe integrated into the cable pulser. This system was used to measure the reverse recovery times (including the creation and charging of the depletion region) for two Avogy gallium nitride diodes; the initial reverse recovery time was found to be 4 ns and varied minimally over reverse biases of 50-100 V and forward current of 1-100 mA.

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TYPE Journal Article YEAR 2017

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An active Thevenin equivalent circuit approach to problems with non-linear circuit loads

Proceedings of the 2017 19th International Conference on Electromagnetics in Advanced Applications, ICEAA 2017

Williams, Jeffery T.; Zutavern, Fred J.; Bacon, Larry D.

The analysis of electromagnetic coupling in nonlinear circuits requires a bidirectional, fully consistent approach. Nonlinear responses of semiconductor devices in electronic circuit components can change the impedances seen at circuit nodes, changing the boundary conditions encountered by impressed electromagnetic fields, and thus changing the characteristics of the energy coupled from these external fields into that circuit. It is important to include the coupling in the circuit simulation self-consistently because this allows us to accurately predict the responses to various EMI/EMC problems of interest. It is also important to predict circuit responses efficiently because that opens the door to statistical applications for the technique being used. In this paper, we review a technique that we have developed called ATHENA (A THevenin Equivalent Network Approach). This approach is shown to be quite robust in that it is computationally efficient, it can be implemented in a variety of commonly available circuit solving codes, it already includes a few additional techniques required to enhance its implementation in those codes, and it is quite accurate.

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TYPE Conference Poster YEAR 2017

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Experiments and Computational Theory for Electrical Breakdown in Critical Components: THz Imaging of Electronic Plasmas

Zutavern, Fred J.; Hjalmarson, Harold P.; Bigman, Verle H.; Gallegos, Richard J.

This report describes the development of ultra-short pulse laser (USPL) induced terahertz (THz) radiation to image electronic plasmas during electrical breakdown. The technique uses three pulses from two USPLs to (1) trigger the breakdown, (2) create a 2 picosecond (ps, 10 -12 s), THz pulse to illuminate the breakdown, and (3) record the THz image of the breakdown. During this three year internal research program, sub-picosecond jitter timing for the lasers, THz generation, high bandwidth (BW) diagnostics, and THz image acquisition was demonstrated. High intensity THz radiation was optically-induced in a pulse-charged gallium arsenide photoconductive switch. The radiation was collected, transported, concentrated, and co-propagated through an electro-optic crystal with an 800 nm USPL pulse whose polarization was rotated due to the spatially varying electric field of the THz image. The polarization modulated USPL pulse was then passed through a polarizer and the resulting spatially varying intensity was detected in a high resolution digital camera. Single shot images had a signal to noise of %7E3:1. Signal to noise was improved to %7E30:1 with several experimental techniques and by averaging the THz images from %7E4000 laser pulses internally and externally with the camera and the acquisition system (40 pulses per readout). THz shadows of metallic films and objects were also recorded with this system to demonstrate free-carrier absorption of the THz radiation and improve image contrast and resolution. These 2 ps THz pulses were created and resolved with 100 femtosecond (fs, 10 -15 s) long USPL pulses. Thus this technology has the capability to time-resolve extremely fast repetitive or single shot phenomena, such as those that occur during the initiation of electrical breakdown. The goal of imaging electrical breakdown was not reached during this three year project. However, plans to achieve this goal as part of a follow-on project are described in this document. Further modifications to improve the THz image contrast and resolution are proposed, and after they are made, images of photo-induced carriers in gallium arsenide and silicon will be acquired to evaluate image sensitivity versus carrier density. Finally electrical breakdown will be induced with the first USPL pulse, illuminated with THz radiation produced with the second USPL pulse and recorded with the third USPL pulse.

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TYPE SAND Report YEAR 2016

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