Correlation between micropipes on SiC substrate and dc characteristics of AlGaN∕GaN high-electron mobility transistors

We report the influence of the size of hollow cores that extend from micropipes in SiC substrates on the dc characteristics of AlGaN∕GaN high-electron mobility transistors (HEMTs) fabricated on the substrates. Significant deterioration of the dc characteristics of HEMTs fabricated in the vicinity of hollow cores with a diameter of 5μm was observed, while no major deterioration was observed for HEMTs fabricated around hollow cores whose diameters were 1.5 and 3μm. A clear correlation between the size of hollow cores and free carrier densities at the peripheries of the cores was observed using micro-Raman imaging. The high densities of free carriers around relatively large hollow cores were suggested to be the cause of deterioration of the dc characteristics of HEMTs fabricated in the vicinity of the hollow cores. The device deterioration length with respect to the hollow core size was empirically deduced, and the effective decrease in the wafer yield was estimated as well.