Switching Megawatts with Power Transistors

It has been know for nearly two decades (shortly before year 2000) that silicon power switching technology had reached material limits. Instead, wide bandgap semiconductors were seen as the next material of choice. Among these, silicon carbide (SiC) and gallium nitride (GaN) are the most promising semiconductors for electrical power switching. Unlike silicon, both SiC and GaN materials contain high density of crystal defects in the drift region of a power semiconductor switch; these defects are primarily caused by defects in the substrate material used for growing the epitaxial layers that support the high voltage. A paradigm shift in the bulk crystal growth of both SiC and GaN materials that leads to a dramatic reduction in the density of bulk crystal defects is needed. In order to impact such a philosophical change, a "reliability-driven" material technology must be pursued as it is guaranteed to lead to the lowest die cost with high manufacturing yield. What is needed is a systematic correlation of drift-region defect density to the current density that can be reliably switched for a given breakdown voltage rating in order to guarantee certain prescribed mean-time-between-failures (MTBF) of power converter under actual field-operating conditions. This requires paradigm shift in the current method of technology development and manufacturing.