Specific features of the metal-insulator conductivity transition in narrow-gap semiconductors of the MgAgAs structure type

Conductivity mechanisms in heavy-doped n-ZrNiSn intermetallic semiconductors

“…The calculations show that the gap width is almost independent on the acceptor impurity concentration. It is also a well agreement with experimental data [8][9][10][11][12][13] (except for above mentioned Refs. [14,15]).…”

“…One can see, that ZrNiSn is a narrow-gap semiconductor; there is a forbidden gap between the valence and conduction bands which width does not depend on the acceptor impurity concentration. This is quite well agreement with theoretical KKR [21] and pseudo-potential [22] calculations and experimental results [8][9][10][11][12][13] as well. As it is clear from Fig.…”

“…2, a doping of the ZrNiSn by the acceptor impurities (via replacing Ni by Co atoms) leads to the nonmonotonous 1/N(E F ) versus Co concentration x dependence. This plot is different from the before discussed case where ZrNiSn semiconductor was doped by the acceptor impurities via the replacing of Zr by Sc atoms and thus the 1/N(E F ) concentration dependence behaved monotonous [7][8][9].…”

“…Our recent experimental and theoretical investigations of magnetic and electrotransport phenomena in the n-ZrNiSn and p-TiCoSb compounds doped by acceptor and/or donor impurities, respectively (N A , N D from 10 19 to 10 21 cm −3 ), allowed us reveal the role of the impurity bands in the conductivity of the intermetallic semiconductors with the MgAgAs structure type, and then to propose an impurity bands reconstruction model for different types of the impurities, and finally we observed the insulator-metal transition predicted by the theoretical calculations [7][8][9][10][11][12]. It has to be noticed that in all the publications cited above acceptor impurities were created by a substitution of the Zr (4d 2 5s 2 ) by Sc (3d 1 4s 2 ) atoms in the crystal structure, whereas the donor ones were created by a substitution of the Co (3d 7 4s 2 ) by the Ni (3d 8 4s 2 ) atoms, respectively.…”

“…[14,15] does not relate to a gap collapse, but to changes in the compensation degree, and as a result to the fact that the Fermi level (E F ), being fixed at first by the Coulomb gap of the impurity band, then drifts towards a continuous energy band with intruding inside it followed, so that the character of the conduction changes from activated to metallic-like [8][9][10][11][12]16,17].…”