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Ozeki Group

Measurement and Control of Surface Reactions for Nano-Structure Fabrication
Masashi Ozeki

ĦObject
@III-V crystals to be investigated in the group are divided into two categories: 1) GaAs, AlAs and InAs crystals and 2) III-V nitride crystals such as GaN. The main purpose of the group is to establish a technological base of nano-structure fabrication and nano-scale impurity control for III-V crystals. To this end, we mainly use chemical reactions between molecules and solid surface.

Chemical reactions of source molecules on solid surface are studied dynamical approach. For this purpose, we have built state-of-the art molecular beam scattering experiments. This allows source molecules to be brought to a well defined semiconductor surface in well characterized ways. We also measure the surface structures by STM and m-RHEED, which are connected by a vacuum tunnel with surface process chambers. These measurements will clarity the initial stage of the crystal growth and etching processes in III-V compounds.

ĦResults in Fiscal Year
@To establish a technological base of nano-structure fabrication for III-V crystals such as GaAs and GaN, we have obtained the following experimental results.

1. A new reaction apparatus, double supersonic beam epitaxy (DSBE) and scattering system, has been developed for the study and control of the surface reaction processes in III-V compounds.

2. High quality GaAs films were, for the first time, grown by DSBE using TEG as Ga source and TBAs as As source without any thermal cracking.

3. A new surface reaction model, which successfully explains the GaAs growth by DSBE, have been proposed.

4. Two types of GaCl cells, which can be used for DSBE, have been developed using DEGaCl source, and Ga and Cl2 sources.

5. Quantitative characterization of excited nitro-gen species emitted from ECR- and RF-type radical sources was carried out by laser induced fluorescence (LIF), emission analysis and ion counting, aiming at the crystal growth of nitride semiconductors by these radical sources. It was found that only the 1st-excited states can reach the reaction surfaces in the crystal growth using remote plasma, and that intensities of excited species are not linear to the discharge power. The ratios among generated excited species was found to depend on the power, the gas flow rate and the type of radical sources.

6. Fundamental properties of the pulsed molecular beam scattering system, which was designed and installed last year, were confirmed. In order to get an excited nitrogen pulsed beam, an apparatus for electron-beam excitation was attached to it, and the nitridation of GaAs surfaces by the pulsed beam was observed. STM observation of the nitridation for Ga-coated Si(111) surfaces were also carried out.

7. In order to observe the crystal growth of nitride semiconductors in-situ, the epitaxial growth observation system by electron beam was designed and installed.

Fig. 1 Reaction system for double supersonic beam epitaxy.

Fig. 2 Growth rate of GaAs layer as a function of growth temperature. Activation energy of 11.8 kcal/mol agrees well with that calculated from the growth model.

Fig. 3 Power dependence of emission intensities from a rf-nitrogen plasma.