We have investigated the site-controlled growth of InAs quantum dots (QDs) by using atomic-force-microscope (AFM)-assisted anodic oxidation. It is found that the morphology of the site-controlled QDs strongly depends on the growth temperature, T g ; when QDs are grown at T g 480 C, the obtained QDs are much larger than the nanoholes prepared by AFM oxidation. In contrast, when QDs are grown at T g ¼ 520 C, the diameter of the QDs is limited by that of nanoholes and is almost unchanged with varying InAs supply. The single-layer QD array grown at 520 C showed good optical properties and uniformities. #

We have investigated the thermal stability of GaAs-oxides grown by atomic force microscope (AFM)-assisted anodic oxidation to identify the conditions suitable for fabricating oxide nanomasks for molecular beam epitaxy (MBE). The oxides grown at bias voltages, V ox, less than 30 V were desorbed after standard thermal cleaning in MBE, while the oxide patterns fabricated at V ox ≥40 V survived on the GaAs surfaces. From X-ray photoemission spectroscopy, we have found that the better thermal stability of AFM-oxides grown at V ox > 40 V can be attributed to the formation of Ga2O3 and that Ga2O3 can be used as nanomasks for site-controlled MBE growth.

We investigate the effect of Ar-ion-beam irradiation during the deposition of SiOx films by dual-ion-beam deposition system. Ion-beam irradiation effectively increases the oxygen content, x, in SiOx films indicative of the preferential sputtering of Si phase as compared to SiO2 phase in SiOx films. We observe the intense photoluminescence from nonirradiated sample after postdeposition annealing at 1100°C indicating the formation of Si nanocrystals as shown by a cross-sectional transmission electron microscope. However, the increased oxygen content in ion-beam-irradiated sample results in small optical volume of small Si nanocrystals not sufficient for yielding appreciable photoluminescence intensity after postdeposition annealing. The property is utilized for achieving the area-selective formation of Si nanocrytals by inserting a shadow mask in assist ion beam during deposition.

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