OTSUKA Laboratory
<Major Research Areas>Thin film growth of semiconductors, Semiconductor physics

Exploration of electron correlation
phenomena in semiconductors
with molecular beam epitaxy

Research activity

　　With molecular beam epitaxy(MBE), we can directly manipulate electron wavefunctions in semiconductor structures by controlling thin-film growth processes on the atomic scale. With this capability MBE has been widely utilized in developments of semiconductor devices which exhibit quantum effects of electron transport and optical phenomena. Such semiconductor devices include high electron mobility transistors(HEMT’s), resonant tunnel diodes(RTD’s) and quantum well lasers, which are playing important roles in the present information technology. Electron transport and optical processes in these devices are essentially based on “behaviors of individual electrons”. As a new approach of manipulating electron wavefunctions with MBE, we are exploring semiconductor structures which exhibit “electron correlation phenomena” such as magnetic and superconducting properties.

　　In this attempt, we have recently found existence of localized spins at high temperatures in pair delta-doped semiconductor structures where donor and acceptor impurities are doped within single atomic planes. This finding implies that we can introduce spin-based phenomena into semiconductors by doping ordinary non-magnetic impurities, in striking contrast with conventional magnetic materials all of which contain magnetic elements such as transition-metal or rare-earth elements. By utilizing these localized spins we are now trying to develop new semiconductor devices for spintronics and open up a new field of condensed matter physics.

　　As a new member of our group, a student will first learn the MBE growth of semiconductor thin films, which is our core experiment, and next learn a variety of characterization techniques of MBE-grown samples such as electron transport, optical and magnetic measurements. By utilizing these techniques, the student will participate in our research program aimed at developing semiconductor devices of the new generation.

Equipment

MBE system, Hall effect measurement system, Physical property measurement system, Photoluminescence spectrometer, X-ray diffractometer, TEM, AFM, Lithography system, Electron spin resonance(ESR) system.

The main research achievements in the past five years

1. K. W. Bae, Mohd. Ambri Mohamed, D. W. Jung, and N. Otsuka, Direct exchange interaction of localized spins associated with unpaired sp electrons in Be doped low-temperature-grown GaAs layers, J. Appl. Phys. in press.
2. D. W. Jung, J. P. Noh and N. Otsuka, Interaction of localized spins in low-temperature-grown GaAs layers, Physica B, 405, 4133-4138(2010).
3. A. Z. M. Touhidul Islam, D. W. Jung, J. P. Noh, and N.Otsuka, Photoluminescence study on heavily donor and acceptor impurity doped GaAS layers grown by molecular-beam epitaxy, J. Appl. Phys., 105, 0935070 (2009).
4. J. P. Noh, S. Iwasaki, D. W. Jung, A. Z. M. Touhidul Islam, and N. Otsuka, Anomalous Hall effect of metallic Be/Si delta-doped GaAs structures, Phys. Rev. B, 75, 195307 (2007).
5. S. Fukushima and N. Otsuka, X-ray diffraction analysis of the structure of antisite arsenic point defects in low-temperature-grown GaAs layer, J. Appl. Phys., 101, 073513 (2007).