<報文>天然黄鉄鉱の半導体的特性(第3報) : 不純物濃度依存性とdバンドの特徴

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概要

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• In the present study, it was found that the donor activation energy ε_1 of the n-type natural pyrite crystals varied rather systematically with the impurity concentration, N_D-N_A, and the carrier concentrations at 4.2°K and in the exhaustion region were almost equal for each smaple. These facts imply that the effective shallow donor level of those pyrite FeS_2 is formed by one sort of donors, which makes it possible to discuss the impurity-concentration dependences of some physical properties as in the case of well-controlled synthetic semiconductors. The donor activation energy ε_3 in the low temperature region became zero at a higher concentration than that of n-Ge (Sb-doped). The maximum or saturation value, |Δρ/ρ|s, of the negative magnetore-sistance for magnetic field variation increased with the increasing impurity concentration and was expected to reach the maximum at a higher concentration than that of n-Ge (Sb). These higher concentrations imply that the donor wave function of pyrite FeS_2 is not so much extended as that of n-Ge (Sb). The effective mass ratio, m^*/m (≅0.4), estimated from the donor activation energy ε_1 (≅0.01 eV) and the dielectric constant κ (=24 obtained by Gillson), however, was not so large as expected from the small mobility. This estimation leads to the inference that the d-conduction band may be rather wide. Further considerations of a diminutive mobility and a large effective mass in the valence band may support the d-band model which is constructed by an e_g-conduction band and a t_<2g>-valence band. The Mott transition concentration estimated from the values of the above m^*/m and ε_1 was consistent with that from the concentration dependence of the resistivity at 4.2°K. This concentration was also higher than that of n-Ge (Sb). The other physical properties are discussed according to the concentration dependences.

• 東北大学の論文
• 1973-11-24

著者

• 堀田 浩充

  東北大学選鉱製錬研究所

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