InP patterning using contact mode and non-contact AFM lithography for quantum dot localization

Abstract

AFM contact and non-contact mode have been used to oxidize InP(001) surface at the nanoscale in order to create, after oxide etching, nano-holes used as nucleation sites for self-assembled quantum dots (QDs). Results obtained in contact mode are similar to those obtained with the local anodization of silicon, and principally explained by the effect of space charges that occurs during the initial stages of the oxide growth. Using a negative pulse permits the experimenter to reduce the space charge effects in the oxide and thus to enhance both homogeneity and resolution. Non-contact mode coupled with a modulated voltage brings even more specific results. For more than two a decade variation of probe velocity (0.01–5 μm s −1), the AFM oxidation introduces no significant changes in the features. Studies on the influence of oxidation time have identified two regimes. With the first one, a high growth rate was found for oxidation times shorter than 100 ms. Second, for oxidation times longer than 100 ms, we observe an oxide height saturation and a lower lateral growth rate. These results provide a way to control separately both depth and diameter of holes. The achievement of non-contact oxidation confirms the compatibility of this technique in both resolution and homogeneity for QD nucleation sites.