On the doping concentration dependence and dopant selectivity of photogenerated carrier assisted etching of 4H–SiC epilayers
By Pavunny, Shojan P.; Myers-Ward, Rachael L.; Daniels, Kevin M.; Shi, Wendy; Sridhara, Karthik; DeJarld, Matthew T.; Boyd, Anthony K.; Kub, Francis J.; Kohl, Paul A.; Carter, Samuel G.; Gaskill, D. Kurt
Published in Electrochimica Acta
2019
Abstract
A comprehensive photogenerated carrier assisted etching investigation is carried out on the Si polar surface of high-quality p- and n-type (0001) 4H–SiC epilayers. The epilayers have intentional or unintentional doping densities in the 1014–1018 cm−3 range. Cyclic voltammetry and chronoamperometry studies under a non-focused above bandgap (280–400 nm) light illumination (≤0.66 Wcm−2) in a highly basic etching medium (1 wt% KOH solution, pH ∼12) complemented by Mott-Schottky characterization reveal a dependence of the etch voltage (within ±1 V) and etch rate (∼20–60 nm/min) on doping concentration and type. Our results demonstrate separate mutually exclusive etch voltage windows (∼± 0.3–0.7 V) in the diffusion-limited regime for a pair of doping concentrations with opposite conductivities to establish smooth preferential etching. These results provide insight in the design and fabrication of higher performance three dimensional SiC homo/hetero-junctions for various applications including photonic crystal cavities.