Model of Formation and Propagation of Nanoporous Structures in Indium Phosphide during Anodisation in Aqueous KOH

Porous layers are formed in highly doped (1018 cm-3) n-type InP anodised in concentrated aqueous KOH solutions. The pores have a characteristic diameter and propagate along A directions. This preferential etching leads to porous regions with a characteristic tetrahedral shape. We have previously proposed a three-step mechanism of electrochemical pore formation: (1) hole generation at pore tips, (2) hole diffusion and (3) electrochemical oxidation of the semiconductor to form etch products. Step 1 determines the overall etch rate. However, if the kinetics of Step 3 are slow relative to Step 2, then etching can occur at preferred crystallographic sites leading to pore propagation in preferential directions. We have implemented the fundamental rules of this mechanism in a numerical simulation of this mechanism and we show that the simulation reproduces many of the features of pore growth in InP.