Sizuo Asanabe

Semiconducting Properties of Chromium Disilicide

The electrical resistivities, Hall coefficients and thermoelectric powers of undoped, Si-doped and Mn-modified CrSi 2 crystals have been measured over the temperature range from 90°K to 1100°K. The undoped crystal is a p -type semiconductor with the hole concentration of about 4×10 20 /cm 3 . The hole concentration is decreased by doping silicon or manganese. Manganese atoms act as donors. Specimens heavily doped with manganese are n -type at low temperatures and change to p -type at high temperatures. Analysis of the experimental results leads to the following conclusions: (1) the forbidden energy gap=0.35 eV, (2) the ratio of the electron mobility to the hole mobility≃0.01 and (3) the density of state effective mass of electrons≃7 m 0 and that of holes≃5 m 0 . Assuming that the effective masses and the mobility ratio do not vary with temperature, the temperature dependence of the thermoelectric powers of the undoped and doped crystals can be explained satisfactorily.

Electrical Properties of Germanium Selenide GeSe

Experimental studies were made of electrical resistivity and Hall coefficient of stoichiometric, non-stoichiometric and impurity-doped GeSe crystals over the temperature range from 100°K to 800°K. The energy gap was estimated to be nearly 1.0 eV from the slope of the resistivity curves at high temperatures. There were two ways in which hole mobility varied with temperature: one was as T -2.0 and the other as T 4.3 . The results on low temperature Hall coefficient were qualitatively interpreted on the assumption that there were two kinds of impurity levels in GeSe, one of which was acceptor level due to the impurity atoms common to all specimens and the other donor level or trapping center of holes due to germanium atoms in excess of stoichiometry. An anomalous behavior found in the Hall coefficient was explained by the same assumption as in the case of SnSe that new acceptors were introduced into GeSe by heat-treatment at high temperatures and that these introduced acceptors were annihilated by the heat-t...

Electrical Properties of Stannous Selenide

The electrical resistivity, Hall coefficient and thermoelectric power were investigated over the temperature range from 100° K to 800° K on pure and impurity-doped SnSe crystals. An anomalous hump of the Hall coefficient was found to occur at about 200°C in most of the as-grown crystals and this seems to make the conventional analysis based on a simple semiconductor model impossible. Anisotropies in the resistivity and Hall coefficient were also studied on single crystals and the observed anisotropy in the resistivity seems to be ascribed to an anisotropy in the effective mass of holes. Hole mobility varies as T -2.0 at high temperatures and its discrepancy from T -1.5 law is explained on the assumption of both optical and acoustical mode scatterings. Further investigation was made of the anomalous Hall coefficient on heating the specimen at various temperatures in vacuum. This anomalous phenomenon was found to depend on the heat-treatment history of the crystal and the experimental results were analysed ...

Conduction Phenomena in Monosilicides of Iron Group Transition Elements

The electrical resistivity, Hall coefficient and thermoelectric power have been measured over the temperature range from 4.2 to 800°K on Co 1- x Mn x Si(\(x{\lesssim}0.06\)), Co 1- x Cr x Si(\(x{\lesssim}0.04\)) and, Co 1- x Cr x Si(\(x{\lesssim}0.10\)) solid solutions. The specimen is n -type when x =0. With increasing x , the specimens of Co 1- x Ni x Si become more n -type, while in the specimens of Co 1- x Mn x Si and Co 1- x Cr x Si, the contribution of hole conduction in-creases. The experimental data are qualitatively interpreted in terms of the overlapping band structure scheme, which is appropriate for Co 1- x Fe x Si solid solutions. It is concluded that the replacement of cobalt with manganese or chromium produces approximately one hole per atom, while the replacement of cobalt with nickel produces approximately one electron per atom in the solid solutions.

Phase Diagram of the Partial System of MnSi-Si

A phase diagram of the system MnSi-Si containing Si in the range from 45.00 to 57.00 wt% is determined by the methods of X-ray, metallographic and thermal analyses and also by the electrical measurements. It is found that the intermetallic compound in this system is MnSi1.72. This compound has the maximum melting point of about 1145°C in the neighboring composition range. A single crystal of MnSi1.72 is obtained by the Czochralski method.