On the pulsed anodic oxidation of n⁺-InP

We have performed a parametric investigation of the anodic oxidation of highly doped n-type InP(100) using a pulsed current source. Approximately 75% of the oxide growth took place within the first ∼ 10 s of oxidation, and the equilibrium oxide thickness was reached soon thereafter The oxide thickness, d_ox, varied linearly with potential difference between electrodes, V, with d_ox ≃ 1 nm/V. This value could be as high as ∼ 1.85 nm/V when optimum conditions are used for anodization. We have also correlated d_ox with the maximum current density, J_max, and observed an exponential dependence. Furthermore, d_ox increased slowly with the increasing duty cycle, η, of the pulse train and reached a maximum for η = 4/6. Highly symmetrical structures consisting of pyramid-shaped protrusions located at the center of circular walls were observed on oxidized surfaces by atomic force microspcopy. To the best of our knowledge, this is the first report of such topographical features on electrochemically oxidized InP surfaces.