Role of the impurity band during the insulator-metal transition as the composition of highly doped and compensated TiCo
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TRONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS
Role of the Impurity Band during the Insulator–Metal Transition as the Composition of Highly Doped and Compensated TiCo1 – xNixSb Semiconductor Alloy Is Varied. Donor Impurities V. A. Romakaa, b, M. G. Shelyapinac, Yu. V. Stadnykd^, D. Frucharte, L. P. Romakad, and V. F. Chekurina aPidstryhach
Institute for Applied Problems of Mechanics and Mathematics, National Academy of Sciences of Ukraine, Naukova Str. 3b, Lviv, 79053 Ukraine bNational University Lvivska Politekhnika, 12 Bandery Str., Lviv, 79013 Ukraine cFock Institute of Physics, St. Petersburg State University, St. Petersburg, 198504 Russia dFranko National University, Kyryl and Mephodiy Str. 6, Lviv, 79005 Ukraine ^e-mail: [email protected] eLaboratoire de Cristallographie, CNRS, BP 166, 38042 Grenoble Cedex 9, France Submitted June 23, 2005; accepted for publication December 1, 2005
Abstract—The role of the impurity donor band in the conductivity of the heavily doped and compensated intermetallic TiCoSb semiconductor is determined. The electronic structure of the TiCo1 – xNixSb semiconductor alloy is calculated. A model of impurity band transformation in the TiCoSb semiconductor due to donor impurity doping is suggested. The transition from activated to metallic conductivity when varying the TiCo1 – xNixSb alloy composition is detected, which we identify with the Anderson transition. PACS numbers: 71.20.Nr, 71.30.+h, 72.20.Pa, 75.20.Ck, 81.05.Hd DOI: 10.1134/S1063782606070074
1. INTRODUCTION When studying the influence of impurities on the kinetic, magnetic, and structural parameters of intermetallic compounds of the MgAgAs structure type, in particular semiconductors MCo(Sn, Sb) (M = Ti, Zr, Hf), we concluded that impurity states play a crucial role in the conductivity of such compounds. This conclusion was based on an analysis of both the theoretical and experimental results obtained by us, and of published data on the conductivity, Seebeck coefficient, and magnetic susceptibility of M(Co, Ni)(Sn, Sb) semiconductors and their alloys, as well as on the study of the structural features of these compounds [1–12]. The influence of acceptor impurities with concentrations from NA = 3.5 × 1020 to 5.3 × 1021 cm–3 on the kinetic and magnetic phenomena in intermetallic semiconductors n-ZrNiSn and n-TiNiSn was studied. Furthermore, the density of electrons was calculated for Zr1 – xScxNiSn and Ti1 – xScxNiSn semiconductor alloys. These studies allowed us to suggest a model of impurity band transformation as a result of doping of these semiconductors with acceptor impurities and to observe the theoretically predicted insulator–metal conductivity transition, which is the Anderson transition [13, 14]. In this context, it is noteworthy that the fabrication technology of these semiconductor materials in all the studies known to us, including the cited ones, is based
on alloying a mixture of initial components, followed by uncontrolled melt cooling. In other words, one of the ways for producing amorphous solid
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