The effect of low temperature InGaAs/GaAs cover layer growth of InAs quantum dots on its optical and structural properties was investigated. Photoluminescence intensity depended heavily on the growth temperature and thickness of low temperature cover layer and decreased as the number of dislocations formed directly above InAs quantum dots increased. These dislocations are formed at the initial stage of high temperature GaAs growth, originating from pits that remain on the surface after the growth of the low temperature cover layer and subsequent annealing. To ensure a high quality InAs quantum dot structure free from dislocations, it is important to obtain a highly flat surface with suppressed pits after low temperature cover layer growth and subsequent annealing.

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InAs quantum dots with InGaAs strain-reducing layer on GaAs(001) grown at three different temperatures were investigated from the aspect of both structural and optical properties. Dislocations originated from the InAs quantum dot (QD) layer were observed at growth temperatures of 490 °C, 500 °C, and 510 °C. Their densities are relatively larger in the cases of 490 °C and 510 °C, where they are caused by strain accumulation at larger-size InAs quantum dots during cover layer growth. Photoluminescence lifetimes at 6 K are almost the same in the three samples. On the other hand, that of the 500 °C-grown sample is an order of magnitude larger than the other two samples at 300 K. This indicates that dislocations act as a non-radiative center to deteriorate optical characteristics. Growth around 500 °C suppresses the growth of larger-size InAs QDs and reduces the InAs strain accumulation, which leads to the dislocation formation at the cover layer.

This paper demonstrates a new technique to form a patterned metal-oxide film on a silicon wafer using a local electric field. The idea of the technique involves using an interaction between metal-organic molecules dissolved in a non-polar solvent and a local electric potential field on a substrate. In this paper, an alkoxide and a metal-organic complex were used as metalorganic precursors. The precursor molecules were selectively deposited at the electrified region of the substrate. The deposited precursor films were heated with an electric furnace to form oxide films. Patterned TiOx and Sr-Ti oxide films were formed on a SiOx/Si substrate. These patterned thin films are potentially applicable to electric and optical devices. We believe that this new technique provides a new bottom-up process of molecular assembly for nanofabrication.

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