Fundamental Studies of Development of Quasicrystalline Semiconducting Films

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Major results obtained are summarized below.1. The stable composition range of quasicrystalline and approximant phases has been determined in the totally five systems Al-Mg-Zn, Al-Mg-Cu, Al-Mg-Ag, Al-Mg-Pd and Mg-Ga-Zn by using mechanical alloying technique. It is found that the stable quasicrystal is formed when the special condition is fulfillled : the electron concentration is in the range 2.15<e/a<2.20 and the Mg content slightly higher than that of the approximant phase.2. Both RT-and Ml-type quasicrystals have been prepared by liquid quenching technique in the Al-Mg-Zn, Al-Mg-Cu and Al-Mg-Pd and Al-Mg-Pd, Al-Cu-Ru and Al-Pd-Re, respectively. The valence band structure has been studied by XPS, SXS and electronic specific heat measurements. It is found that the valence band structure is described by the free electron picture except for the presence of the pseudogap near the fermi level in the RT-type quasicrystals. The d-band in the Ml-type quasicrystals is widely spread over the valence band energy range and the Al-3p electron distribution is heavily distorted from the free electron-ike one observed in pure Al. As a result, the spiky density of states is sharpened in the Ml-type quasicrystals as compared with the free electron-like RT-type quasicrystals.3. The characteristic features of the valence band structure for Ml- and RT-type quasictystals observed by the above measurements have been reflected in the electron transport properties. The conductivity and electronic specific heat coefficient have been well described by the carrier concentration deduced from the Hall coefficient, regardless of whether Ml-or RT-types are involved. From this we conclude that either electrons or holes dominate at the Femi level in most quasicrystals.4. We could successfully synthesize the Al-Od-Mn thin films by laser abration method.