A simple method to enhance atomic force microscopy local oxidation by coating the substrate with a thin layer of gold is reported. The effect of gold coating is demonstrated experimentally by atomic force microscopy oxidation at various thicknesses of gold on Si and InP. Oxide heights reaching 30nm are easily achieved on silicon at rates 10 times greater than traditional methods. The gold layer is assumed to increase conductance and current during oxidation, thereby reducing decline in growth rates caused by the increasing resistance of the growing oxide layer itself. Improvement in growth rate and height increases with increasing gold thickness up to a maximum height, but beyond that thickness the heights and rates decrease because the gold layer itself becomes a barrier to the migration of oxyions. The presented method is demonstrated to improve the oxidation rate and height on normal and highly resistive substrates, with lower requirements for applied voltage during oxidation.

Local oxidations of InN and GaN were realized using an atomic force microscope (AFM). InN was oxidized easily by traditional AFM oxidation to ∼40 nm oxide height. The same AFM methodology was applied to GaN, which exhibited only minimum oxidation even at 10 V and high humidity. However, further experimentation led to successful nano-oxidation of GaN by two different techniques. In the first technique, a ∼10 nm gold film was deposited by sputtering onto the clean GaN substrate. The gold film reduced the AFM oxidation circuit resistance and increased the oxyanion driving current (oxidation current), thereby allowing AFM oxidation with heights reaching ∼25 nm at a humidity of 70%, but with a danger of gold contamination of the oxide. To eliminate this danger, additional experiments were performed in which the gold film on the GaN was removed in a small area, after which AFM oxidation was successfully performed in the area with gold removed with oxidation heights comparable to those of the gold-covered GaN. The techniques in this study make possible fast, chemical-free and contamination-free AFM nano-oxidation for metal–oxide–semiconductor field effect transistors based on two important nitrides.

Successful deep and alignment-free patterned etching on GaN using atomic force microscope (AFM) local oxidation followed by in-situ chemical etching is demonstrated. Oxide ridges are grown on GaN on an AFM by applying positive sample bias at 80% humidity, with the oxidation reaction expedited by UV light. The oxide ridges are then etched by HCl solution, leaving troughs in the GaN surface. A dripping strategy for the in-situ chemical etching is recommended that allows deep, alignment-free multiple AFM oxidation/etching works on the GaN surface without any need of substrate removal from the AFM platform. Repeated etching followed by AFM oxidation on a spot on a GaN surface resulting in a hole as deep as 800 nm was also demonstrated. Further, a preliminary evaluation of the porosity of the AFM-grown oxide indicates that the oxide ridges grown on GaN at an AFM cantilever moving speed of 300 nm/s are porous in structure, with an estimated porosity of 86%, which porosity could be reduced if longer resident time of the AFM cantilever on the target oxidation region was used.