Growth and characterization of 3C?SiC and 2H?AlN/GaN films and devices produced on step-free 4H?SiC mesa substrates

While previously published experimental results have shown that the step-free (0?0?0?1) 4H?SiC mesa growth surface uniquely enables radical improvement of 3C?SiC and 2H?AlN/GaN heteroepitaxial film quality (>100-fold reduction in extended defect densities), important aspects of the step-free mesa heterofilm growth processes and resulting electronic device benefits remain to be more fully elucidated. This paper reviews and updates recent ongoing studies of 3C?SiC and 2H?AlN/GaN heteroepilayers grown on top of 4H?SiC mesas. For both 3C?SiC and AlN/GaN films nucleated on 4H?SiC mesas rendered completely free of atomic-scale surface steps, TEM studies reveal that relaxation of heterofilm strain arising from in-plane film/substrate lattice constant mismatch occurs in a remarkably benign manner that avoids formation of threading dislocations in the heteroepilayer. In particular, relaxation appears to occur via nucleation and inward lateral glide of near-interfacial dislocation half-loops from the mesa sidewalls. Preliminary studies of homojunction diodes implemented in 3C-SiC and AlN/GaN heterolayers demonstrate improved electrical performance compared with much more defective heterofilms grown on neighbouring stepped 4H?SiC mesas. Recombination-enhanced dislocation motion known to degrade forward-biased 4H?SiC bipolar diodes has been completely absent from our initial studies of 3C?SiC diodes, including diodes implemented on defective 3C?SiC heterolayers grown on stepped 4H?SiC mesas.