Formation of superhydrophobic porous GaAs layer: effect of substrate doping type

In this report, the effect of the GaAs substrate type on the surface hydrophobicity of porous GaAs layers produced by an electrochemical etching method is investigated. At an etching time of 60 min, the porous GaAs layer formed on p+-type GaAs substrate shows a hydrophobic surface with advancing water contact angle (θa) of around 140°, and a wetting hysteresis of ~17.5°. Under the same equivalent etching conditions and parameters, the layer formed on n+-type GaAs substrate exhibits self-cleaning superhydrophobic surface with advancing θa ≈ 158°, and a wetting hysteresis of ~2.4°. This is attributed to doping type-induced morphological and structural modifications of porous GaAs layer, as it is inferred from scanning electron microscopy, atomic force microscopy, Raman scattering and X-ray photoelectron spectroscopy results and analysis. The layer formed on n+-type substrate shows a β-Ga2O3-rich surface of micrometre-sized cone-like textures composed of bunched nano-wires, whereas the layer formed on p+-type substrate exhibits an As2O3-rich micron-sized grooved structure. Superhydrophobic porous GaAs is of interest for prospective photovoltaic and sensing applications.