Effect of current density on pore formation in n-InP in KOH

InP samples which were galvanostatically anodised in 5 mol dm^-3 KOH exhibited crystallographic pore etching at current densities ranging from 1 mA cm^-2 to 20 mA cm^-2. Surprisingly, the total charge at growth termination (∼1.8 C cm^-2) and the corresponding layer thickness (∼3.0 μm) were independent of current density in experiments at continuous constant current. Surface pit density was proportional to current density, indicating that the average current per pit was 1.7 pA, independent of current density. The influence of mass transport on the termination of porous layer growth was demonstrated in an experiment at low current density where the current was interrupted a number of times before layer growth ended. At low current densities, pores had sharp tips, triangular cross-sections and large pore widths. At higher current densities, both the pore tips and the pore cross-sections became more rounded while the pore width decreased. These variations are explained in terms of the effect that different rates of hole supply (at different current densities) can have on the rate of indium vacancy formation on the three {111}A faces that make up the pore tip.