76 research outputs found
Superconductivity in silicon nanostructures
We present the findings of the superconductivity observed in the silicon
nanostructures prepared by short time diffusion of boron on the n-type Si(100)
surface. These Si-based nanostructures represent the p-type ultra-narrow
self-assembled silicon quantum wells, 2nm, confined by the delta - barriers
heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the
delta - barriers appear to consist of the trigonal dipole centres, which are
caused by the negative-U reconstruction of the shallow boron acceptors. Using
the CV and thermo-emf techniques, the transport of two-dimensional holes inside
SQW is demonstrated to be accompanied by single-hole tunneling through these
negative-U centres that results in the superconductivity of the delta -
barriers. The values of the correlation gaps obtained from these measurements
are in a good agreement with the data derived from the temperature and magnetic
field dependencies of the magnetic susceptibility, which reveal a strong
diamagnetism and additionally identify the superconductor gap value.Comment: 4 pages, 6 figures, presented at the 4th International Conference on
Vortex Matter in Superconductors, Crete, Greece, September 3-9, 200
Registration of terahertz irradiation with silicon carbide nanostructures
The response to external terahertz (THz) irradiation from the silicon carbide
nanostructures prepared by the method of substitution of atoms on silicon is
investigated. The kinetic dependence of the longitudinal voltage is recorded at
room temperature by varying the drain-source current in the device structure
performed in a Hall geometry. In the frameworks of proposed model based on the
quantum Faraday effect the incident radiation results in the appearance of a
generated current in the edge channels with a change in the number of magnetic
flux quanta and in the appearance of features in the kinetic dependence of the
longitudinal voltage. The generation of intrinsic terahertz irradiation inside
the silicon carbide nanostructures is also revealed by the
electrically-detected electron paramagnetic resonance (EDEPR) measured the
longitudinal voltage as a function of the magnetic field value.Comment: 11 pages, 6 figure
Terahertz emission from silicon carbide nanostructures
For the first time, electroluminescence detected in the middle and far
infrared ranges from silicon carbide nanostructures on silicon, obtained in the
framework of the Hall geometry. Silicon carbide on silicon was grown by the
method of substitution of atoms on silicon. The electroluminescence from the
edge channels of nanostructures is induced due to the longitudinal drain-source
current. The electroluminescence spectra obtained in the terahertz frequency
range, 3.4, 0.12 THz, arise due to the quantum Faraday effect. Within the
framework of the proposed model, the longitudinal current induces a change in
the number of magnetic flux quanta in the edge channels, which leads to the
appearance of a generation current in the edge channel and, accordingly, to
terahertz radiation.Comment: 10 pages, 9 figure
Room-temperature quantum oscillations of static magnetic susceptibility of silicon-carbide epitaxial layers grown on a silicon substrate by the method of the coordinated substitution of atoms
The article presents the results of measurement and analysis of the field
dependences of the static magnetic susceptibility of thin epitaxial silicon
carbide films grown on the (110) surface of single-crystal silicon by the
method of the coordinated substitution of atoms. In weak magnetic fields, the
occurrence of two quantum effects at room temperature was experimentally found:
the hysteresis of the static magnetic susceptibility and, in the field
dependences, quantum Aharonov-Bohm oscillations of the static magnetic
susceptibility. The simultaneous occurrence of these effects is a consequence
of two- and one-particle interference of charge carriers (two-dimensional
holes) on microdefects consisting of dipole centers with negative correlation
energy (negative-U dipole centers).Comment: 8 pages, 2 figure
Квантовая лестница дырочной проводимости в кремниевых наносандвичах
The results of studying the quantum conductance staircase of holes in one−dimensional channels obtained by the split−gate method inside silicon nanosandwiches that are the ultra−narrow quantum well confined by the delta barriers heavily doped with boron on the n−type Si (100) surface are reported. Since the silicon quantum wells studied are ultra−narrow (~2 nm) and confined by the delta barriers that consist of the negative−U dipole boron centers, the quantized conductance of one−dimensional channels is observed at relatively high temperatures (T > 77 K). Further, the current−voltage characteristic of the quantum conductance staircase is studied in relation to the kinetic energy of holes and their sheet density in the quantum wells. The results show that the quantum conductance staircase of holes in p−Si quantum wires is caused by independent contributions of the one−dimensional (1D) subbands of the heavy and light holes; these contributions manifest themselves in the study of square−section quantum wires in the doubling of the quantum−step height (G0 = 4e2/h), except for the first step (G0 = 2e2/h) due to the absence of degeneracy of the lower 1D subband. An analysis of the heights of the first and second quantum steps indicates that there is a spontaneous spin polarization of the heavy and light holes, which emphasizes the very important role of exchange interaction in the processes of 1D transport of individual charge carriers. In addition, the field−related inhibition of the quantum conductance staircase is demonstrated in the situation when the energy of the field−induced heating of the carriers become comparable to the energy gap between the 1D subbands. The use of the split−gate method made it possible to detect the effect of a drastic increase in the height of the quantum conductance steps when the kinetic energy of holes is increased; this effect is most profound for quantum wires of finite length, which are not described under conditions of a quantum point contact. In the concluding section of this paper we present the findings for the quantum conductance staircase of holes that is caused by the edge channels in the silicon nanosandwiches prepared within frameworks of the Hall. This longitudinal quantum conductance staircase, Gxx, is revealed by the voltage applied to the Hall contacts, Vxy, to a maximum of 4e2/h. In addition to the standard plateau, 2e2/h, the variations of the Vxy voltage appear to exhibit the fractional forms of the quantum conductance staircase with the plateaus and steps that bring into correlation respectively with the odd and even fractional values.Представлены результаты изучения квантовой лестницы проводимости дырок в одномерных каналах, полученных методом расщепленного затвора внутри кремниевых наносандвичей, которые представляют собой сверхузкую квантовую яму, ограниченную дельта−барьерами, сильно легированными бором на поверхности n−типа Si (100). Так как исследуемая кремниевая квантовая яма является сверхузкой (~2 нм) и ограниченной дельта−барьерами, которые состоят из дипольных центров бора с отрицательной корреляционной энергией, квантовая лестница проводимости одномерных каналов наблюдается при относительно высоких температурах (T > 77 К). Кроме того, квантовая лестница проводимости исследована в зависимости от кинетической энергии дырок и их двумерной плотности в квантовых ямах. Показано, что квантовая лестница дырочной проводимости в р−Si квантовых проволоках обусловлена независимыми вкладами одномерных (1D) подзон тяжелых и легких дырок. Эти вклады проявляются при изучении квантовых проволок квадратного сечения в удвоении амплитуды квантовой ступени (G0 = 4e2/h), исключая первую ступень (G0 = 2e2/h) из−за отсутствия вырождения нижней 1D подзоны. Анализ высоты первой и второй квантовых ступеней указывает на существование спонтанной спиновой поляризации тяжелых и легких дырок, что подчеркивает очень важную роль обменного взаимодействия в процессах одномерного транспорта одиночных носителей. Кроме того, тушение квантовой лестницы дырочной проводимости в электрическом поле проявляется в ситуации, когда энергия полевого разогрева носителей становится сравнимой с энергетической щелью между 1D подзонами. Использование метода расщепленным затвором позволило обнаружить эффект резкого увеличения высоты квантовых ступеней проводимости, когда кинетическая энергия дырок увеличивается. Этот эффект является наиболее сильным для квантовых проволок конечной длины, которые нельзя описать в рамках квантового точечного контакта. Приведены результаты для квантовой лестницы дырочной проводимости, краевыми каналов в кремниевых наносандвичах, выполненных в рамках холловской геометрии. Эта продольная квантовая лестница проводимости, Gxx, выявляется при приложении напряжения к холловским контактам Vху и достигает максимума при 4е2/h. В дополнение к стандартному плато (2e2/h) варьирование напряжения Vxy выявляет дробные значения квантовой лестницы дырочной проводимости с плато и ступенями, величины которых коррелируют с четными и нечетными дробными значениями
Circularly polarized electroluminescence from silicon nanostructures heavily doped with boron
The circularly polarized electroluminescence (CPEL) from silicon
nanostructures which are the p-type ultra-narrow silicon quantum well (Si-QW)
confined by {\delta}-barriers heavily doped with boron, 5 10^21 cm^-3, is under
study as a function of temperature and excitation levels. The CPEL dependences
on the forward current and temperature show the circularly polarized light
emission which appears to be caused by the exciton recombination through the
negative-U dipole boron centers at the Si-QW {\delta}-barriers interface
- …