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Appendix D. Site Reports—Japan 287
for Exotic Nano Materials (Knoll). The emphasis is on basic research, rather
than on applications (this was explicitly stated).
RESEARCH AND DEVELOPMENT HIGHLIGHTS
Dr. Aoyagi gave the WTEC team an introduction to some of his team’s
research activities.
Quantum wire growth: they used a technique similar to that developed by
Kapon for the growth of (primarily) GaAs/AlGaAs and GaP/AlGaP quantum
wires. The attempt was to improve that process and gain better control of the
growth process, with a higher selectivity of incorporation, using the fact that
the growth rates on the (111)A plane is minimal to zero. Measurements
were done in a 40 T magnetic field; the researchers expected to observe a
diamagnetic shift in the luminescence peak under the high field conditions,
and obtained 123 µeV/T 2 for the LH transition and 210 µeV/T 2 for the HH
transition. These are far larger shifts than expected (110 µeV/T 2 for bulk
and 20 µeV/T 2 for 2-D systems). Aoyagi attributes the discrepancy to the
influence of the interaction of the electrons in the wire with the adjacent
impurities.
Si nanostructure formation: these studies began with amorphous silicon
deposited onto Si substrates and annealed in a hydrogen or nitrogen ambient.
The result was the formation of Si nanocrystals, ~ 7 nm in size, embedded
within an amorphous matrix. Emission in the blue was observed, with about
10 -5 stated efficiency. Emission at 420 nm and 380 nm was observed.
Simulations have been carried out to look at the effects of confinement on
the relative regions of the amorphous and crystalline areas (Figure D.8).
amorphous
2.17 nm
crystalline
2.72 nm
Figure D.8. Effects of confinement on the relative regions of the amorphous and crystalline
areas.