Research history:

Using scanning probe microscopes such as scanning tunneling microscope (STM) and scanning near-field optical microscope (SNOM), he has investigated the optical and electronic properties of individual semiconductor nanostructures. Especially, he revealed the electron transport in quantum well (QW) structures, the emission properties of single quantum dots (QDs), the formation mechanism of misfit dislocation in strained QW structures, and the local electronic structures of dilute magnetic semiconductors. These data contributed for the understanding of the properties of semiconductor nanostructures.

Real-space observation of electron transport in quantum structures:

By measuring STM-induced light emission from GaAs QWs on a cleaved (110) surface of AlGaAs/GaAs QW structures, he succeeded to determine two decay lengths of electrons injected into the structures with a precision of a few nanometers. To understand the origin of the decay lengths, he developed Monte Carlo simulation method, in which the quantum size effect and the relevant boundary conditions are taken into account. As a result, the two decay lengths were found to correspond to the thermalization length and the diffusion length of the injected electrons.

Optical properties of single nanostructures:

By mapping the STM-induced light emission intensity from self-assembled InAs/AlGaAs QDs, he succeeded to measure the light intensity images of single QDs with a special resolution of about 25 nm. It was found that the emission linewidth of individual dots is much narrower that the photoluminescence linewidth for an ensemble of QDs and increases with increasing Al content. Moreover, he is investigating the optical properties of one-dimensional nanostructures using SNOM. The light intensity image of single ZnS nanobelts showed that green emission comes from planar defects that are peculiar to the nanobelt structure. He also found optical waveguide behavior of In₂O₃ nanowires for different wavelengths.