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Investigating Dislocations and Stacking Faults in SiC by Electro- and Photoluminescence Imaging
Robert E. Stahlbush
Naval Research Laboratory
When: Friday, October 07, at 2:00 PM
Where: Swearingen Center Rm 3A75
While SiC has numerous advantages for use in power devices, there are a number of material and processing problems that must be overcome before SiC devices are commercially viable. One of the major material problems impeding PiN diode development is the formation of stacking faults (SFs) during forward-biased operation. A powerful technique for studying dislocations and SFs in SiC is electroluminescence. Movies of the light emission from PiN diodes operating at room temperature show the simultaneous growth of SFs and increase in the forward voltage drop. The SFs are quantum wells that reduce carrier lifetime in the diode drift region. The resulting decrease in conductivity modulation increases the forward voltage drop. The mechanisms of stacking fault are discussed. The SFs appear to originate from basal plane dislocations (BPDs) introduced during the epitaxial growth. In addition to BPDs that propagate from the substrate wafer into the epitaxial layer, examples of BPDs that originate during the epitaxial growth are shown. These BPDs can either start during the n- drift growth or at the transition to p+ to start the anode growth. All of these BPDs exhibit the tendency to convert to threading dislocations and the result is that only segments of the dislocations lie in the basal plane. The lengths of these segments range from hundreds of microns to a micron or smaller. By tracking the early growth of the stacking faults – current density x time < 0.1 A-sec/cm2 – the Burgers vector of the original perfect dislocations are determined. They are all either parallel or antiparallel to the offcut direction. The early growth patterns also clearly illustrate the role that kinks play in partial dislocation motion. One drawback of the standard electroluminescence technique is the necessity to fabricate PiN diodes. Two alternatives have been investigated. Patterned aluminum deposited on wafers with a grown pn junction can mimic the operation of a PiN diode using a guard ring to confine current to a small area of the wafer. The second alternative is to image the photoluminescence induced by a UV LED. The pros and cons of each approach will be discussed.
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