Effect of temperature and magnetic field on disorder in semiconductor structures
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ONIC PROPERTIES OF SOLID
Effect of Temperature and Magnetic Field on Disorder in Semiconductor Structures N. V. Agrinskaya* and V. I. Kozub Ioffe Physical–Technical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia *e-mail: [email protected] Received August 10, 2016
Abstract—We present the results of consistent theoretical analysis of various factors that may lead to influence of temperature and external magnetic field on disorder in semiconductor structures. Main attention is paid to quantum well (QW) structures in which only QWs or both QW and barriers are doped (the doping level is assumed to be close to the value corresponding to the metal–insulator transition). The above factors include (i) ionization of localized states to the region of delocalized states above the mobility edge, which is presumed to exist in the impurity band; (ii) the coexistence in the upper and lower Hubbard bands (upon doping of QWs as well as barriers); in this case, in particular, the external magnetic field determines the relative contribution of the upper Hubbard band due to spin correlations at doubly filled sites; and (iii) the contribution of the exchange interaction at pairs of sites, in which the external magnetic field can affect the relation between ferromagnetic and antiferromagnetic configurations. All these factors, which affect the structure and degree of disorder, lead to specific features in the temperature dependence of resistivity and determine specific features of the magnetoresistance. Our conclusions are compared with available experimental data. DOI: 10.1134/S1063776117010095
1. INTRODUCTION It is well known that the main source of resistance of conductors on both sides of a metal–insulator transition is a certain type of disorder, viz., static disorder (impurities) or dynamic disorder (phonons). At the same time, the degree of static disorder is usually treated as a certain property of the material itself, which is independent of external factors such as temperature or magnetic field. This statement is almost indisputable for typical metals, in which disorder is associated with structure defects with characteristics that are not affected by these factors. However, this statement is not so obvious for semiconductor structures in which the main sources of static disorders are charged defects that can be in various charge states. These charge states may depend on temperature due to the redistribution of charge among different states. In addition, if an impurity center allows double occupancy (so-called upper Hubbard band), the form of filling of such centers can also depend on the external magnetic field due to spin correlations. It will be shown below that the dependence of the degree of the disorder on temperature and external magnetic field is determined by a number of factors. As a result, the sample resistance exhibits additional (apart from classical) dependences on the magnetic field and temperature.
It will be shown that these factors are manifested mos
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