Магнітоопір та намагніченість кремнієвих мікроструктур за низьких температур

Abstract

Досліджено особливості перенесення носіїв заряду мікрокристалів кремнію, легованих бором, до концентрацій, які відповідають переходу метал–діелектрик, та нікелем, що міститься у приповерхневій області кристала. Досліджено магнітні властивості до 4 кОЕ та магнітоопір ниткоподібних мікрокристалів кремнію під дією магнітних полів до 14 Тл за температур 4,2 К. Виконано детальний аналіз результатів теоретичних досліджень магнітних та магнітотранспортних властивостей Si<B, Ni>. Встановлено квадратичний характер залежності коефіцієнта від’ємного магнітоопору від намагніченості в ниткоподібних мікрокристалах кремнію.

Investigation of diluted semiconductors in the field of magnetoelectronics opens a possibility to design high sensitive sensors of a magnetic field. On the other hand, study of device performances in hard conditions, namely at cryogenic temperatures, including the temperatures of liquid helium, is an important problem. In this work, considerable attention is paid to establishing the relationship between magnetic and magneto-trasport properties of silicon microcrystals doped with nickel and boron to concentrations in the vicinity of the metaldielectric phase transition, which is important in the development of magnetic field sensors, spin valves, etc. The peculiarities of charge carrier’s transfer in silicon microcrystals doped with nickel impurities, located in the near-surface area of the crystal, are investigated. The magnetization of up to 0.4 Т and the magnetoresistance of silicon microcrystals under the action of magnetic fields up to 14 T in the low temperature range down to 4.2 K were studied. A detailed analysis of the results of theoretical studies of magnetic and magnetic transport properties of Si<B, Ni> whiskers was carried out. The quadratic nature of the dependence of the negative magnetoresistance on the magnetization in silicon microcrystals is established for the magnetization exceeding 5∙105 A/m. However, for small values of magnetization up to 5∙105 A/m, the quadratic dependence of the magnetoresistance on the magnetization is violated, which is connected with the hopping mechanism of carrier transport over one occupied impurity levels. The coefficient of proportionality between the magnetoresistance and the magnetization of the crystals increases if the impurity concentration increases, approaching the metal-dielectric transition, and at temperature decrease. The maximum value of the negative magnetoresistance coefficient for the investigated Si<B, Ni> samples is about 10 %, corresponding to the magnetization of the sample, equal to 6.53∙105 A/m. It was established that the reason of the low-temperature transfer of charge carriers for silicon microcrystals doped by a boron and nickel impurities to the concentration corresponding to the metaldielectric transition is the polarization hopping conductivity in the field of magnetic impurity. The large magnitudes of the negative magnetoresistance correspond to the hopping conductivity of charge carriers by twice occupied admixture states. It was established that the introduction of a magnetic impurity could affect the electromagnetic properties of the crystal associated with the transport of charge carriers by hopping tunneling in the near-surface zone. The results of lowtemperature properties of silicon microcrystals doped with boron and nickel can form the basis of the development of sensitive sensors of a magnetic field with a magnetoresistive principle of operation, including multifunctional sensors.