Photoelectrochemical Properties of p- and n- Type 4H-SiC Epilayers: Doping Concentration Dependence and Dopant Selectivity

Abstract

Exceptional chemical stability resulting from a large bandgap and low-lying valence band edge narrows the wet-etching based micromachining choices of the covalently bonded electronic and photonic device material, SiC, to mainly photoelectrochemical (PEC) dissolution. The PEC etching process has an anisotropic nature with the accompanying advantages of dopant, bandgap, and spatial selectivity, light intensity dependence, reduced ion damage, and the ability to undercut heterostructures. For the first time, a comprehensive photogenerated minority carrier assisted etching investigation was carried out on Si polar surface of high-quality (micropipe density <1 cm-2) p- and n- type (0001) 4H-SiC epilayers having intentional or unintentional doping densities in the 1014–1018 cm-3 range. Cyclic voltametry and chronoamperometry studies under a parallel supra-bandgap (~320 nm) light illumination with varying intensities (≤0.85 Wcm-2) in a highly basic etching medium (1 wt% KOH solution, pH ~12) revealed the dependence of etch voltage and etch rate (~30–90 nm/min) on type and concentration of doping. In addition, a mutually exclusive etch voltage window (~±0.3–0.5 V versus saturated calomel electrode) was established for both types of conductivities in the diffusion-limited regime. Results to be presented can provide key insight in design and fabrication for higher performance three dimensional SiC homojunctions for various applications including photonic crystal cavities.