Date of Award

1-1-2012

Document Type

Campus Access Dissertation

Department

Electrical Engineering

First Advisor

Grigory Simin

Abstract

There has been continued and increasing interest over the past few years in the areas of wide bandgap power electronics for high speed, high power and high efficiency switches which enable innovative approaches to compact pulse power system design and implementation. In the area of high speed pulse technology, optical techniques are clearly superior to conventional electrical methods, in addition to fast and jitter free switching optical driving mechanism provides complete galvanic isolation as well as enhances the reliability and EMI immunity of the whole system.

This research work discusses the effort in developing this technology through design, processing and experiments with wide bandgap materials. Specifically, optically controlled 4H-SiC junction devices have been demonstrated, modeled and analyzed. The behavior and response of different device types and geometries are discussed in terms of junction capacitances, inherent hole traps, optical intensity and absorption coefficients. A physical device model was validated by experimental results, from which on-state resistance and peak photocurrent under different bias conditions and optical energies were calculated, and the potential of these devices was further explored.

Analyses show that slow transient responses under low optical illumination occur due to trapping and detrapping of photo-holes in the space charge region and under CW illumination earlier breakdown observed due to quantum mechanical tunneling as a result of trap enhanced electric field in the depletion region. Transient response under high optical illumination with the improved device geometry was studied details to find out the load invariant switching performances. These works indicate that optically activated SiC power devices which combine the benefits of both SiC power electronics and optical-driving mechanism, together with the capability of reducing the optical-triggering power without compromising on the switching speed, is a desirable device technology for a wide range of pulsed power applications.

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