Evidence for Charging Effects in CdTe/CdMgTe Quantum Point Contacts

Here we report on fabrication and low temperature magnetotransport measurements of quantum point contacts patterned from a novel two-dimensional electron system - CdTe/CdMgTe modulation doped heterostructure. From the temperature and bias dependence we ascribe the reported data to evidence for a weakly bound state which is naturally formed inside a CdTe quantum constrictions due to charging effects. We argue that the spontaneous introduction of an open dot is responsible for the replacement of flat conductance plateaus by quasi-periodic resonances with amplitude less than 2e^{2}/h, as found in our system. Additionally, below 1 K a pattern of weaker conductance peaks, superimposed upon wider resonances, is also observed.Comment: 4 pages, 4 figure

Spin currents in diluted magnetic semiconductors (extended version)

Spin currents resulting in the zero-bias spin separation have been observed in unbiased diluted magnetic semiconductor structures (Cd,Mn)Te/(Cd,Mg)Te. The pure spin current generated due to the electron gas heating by terahertz radiation is converted into a net electric current by application of an external magnetic field. We demonstrate that polarization of the magnetic ion system enhances drastically the conversion due to the spin-dependent scattering by localized Mn(2+) ions and the giant Zeeman splitting.Comment: 6 pages, 4 figure

Magneto-resistance quantum oscillations in a magnetic two-dimensional electron gas

Magneto-transport measurements of Shubnikov-de Haas (SdH) oscillations have been performed on two-dimensional electron gases (2DEGs) confined in CdTe and CdMnTe quantum wells. The quantum oscillations in CdMnTe, where the 2DEG interacts with magnetic Mn ions, can be described by incorporating the electron-Mn exchange interaction into the traditional Lifshitz-Kosevich formalism. The modified spin splitting leads to characteristic beating pattern in the SdH oscillations, the study of which indicates the formation of Mn clusters resulting in direct anti-ferromagnetic Mn-Mn interaction. The Landau level broadening in this system shows a peculiar decrease with increasing temperature, which could be related to statistical fluctuations of the Mn concentration.Comment: 8 pages, 6 figure

Fractional Quantum Hall Effect in a Diluted Magnetic Semiconductor

We report the observation of the fractional quantum Hall effect in the lowest Landau level of a two-dimensional electron system (2DES), residing in the diluted magnetic semiconductor Cd(1-x)Mn(x)Te. The presence of magnetic impurities results in a giant Zeeman splitting leading to an unusual ordering of composite fermion Landau levels. In experiment, this results in an unconventional opening and closing of fractional gaps around filling factor v = 3/2 as a function of an in-plane magnetic field, i.e. of the Zeeman energy. By including the s-d exchange energy into the composite Landau level spectrum the opening and closing of the gap at filling factor 5/3 can be modeled quantitatively. The widely tunable spin-splitting in a diluted magnetic 2DES provides a novel means to manipulate fractional states

Enhancement of the spin-gap in fully occupied two-dimensional Landau levels

Polarization-resolved magneto-luminescence, together with simultaneous magneto-transport measurements, have been performed on a two-dimensional electron gas (2DEG) confined in CdTe quantum well in order to determine the spin-splitting of fully occupied electronic Landau levels, as a function of the magnetic field (arbitrary Landau level filling factors) and temperature. The spin splitting, extracted from the energy separation of the \sigma+ and \sigma- transitions, is composed of the ordinary Zeeman term and a many-body contribution which is shown to be driven by the spin-polarization of the 2DEG. It is argued that both these contributions result in a simple, rigid shift of Landau level ladders with opposite spins.Comment: 4 pages, 3 figure

Пленки ALD Al2O3, SiNx и SiON в качестве пассивирующих покрытий в AlGaN/GaN HEМТ

The effect of passivating ALD Al2O3, SiNx and SiON coatings of different thicknesses on the change in the charge and density of states of AlGaN/GaN heterostructures are studied. The electrophysical parameters of the structures were evaluated using C-V characteristics measured at different frequencies and I-V characteristics. Based on the considered zone diagrams of structures with different control voltages and the evaluation of the elemental composition of the films by Auger spectroscopy, it was shown that the cause of the formation of a large positive charge upon deposition of ALD Al2O3 and SiNx films is the appearance of an additional piezoelectric charge in the AlGaN buffer layer. It is shown that the use of SiON films with an oxygen concentration of more than 3% does not lead to the formation of an additional positive charge, but can cause current fluctuations when measuring I-V characteristics. A possible mechanism of carrier transport in the SCR region, leading to such fluctuations, is considered.В полевых транзисторах на основе широкозонных нитридных гетероструктур широко используются диэлектрические слои в качестве как одного из основных элементов в активных областях приборов, так и пассивирующих слоев. К диэлектрикам предъявляются жесткие требования по высокой диэлектрической проницаемости, большой ширине запрещенной зоны, сплошности покрытия. Кроме того, пленки должны выдерживать высокие электрические поля и иметь низкую плотность поверхностных состояний на границе диэлектрик/полупроводник. Для этих целей в качестве эффективных покрытий обычно используются низкотемпературные пленки, выращенные с помощью плазмохимического осаждения из газовой фазы, атомно-слоевого осаждения (ALD) и плазменно-стимулированного осаждения. Для гетероструктур AlGaN/GaN наиболее перспективными и чаще всего используемые являются пленки ALD Al2О3, SiNх (Si3N4), SiON, ALD AlN.Исследовано влияние пассивирующих покрытий ALD Al2O3, SiNx и SiON разной толщины на изменение заряда и плотности состояний гетероструктур AlGaN/GaN. Электрофизические параметры структур оценивались с помощью C—V-характеристик, измеренных на разных частотах, и I—V-характеристик. На основании рассмотренных зонных диаграмм структур при разном управляющем напряжении и оценки элементного состава пленок методом Оже-спектроскопии показано, что причиной образования большого положительного заряда при нанесении пленок ALD Al2O3 и SiNx является возникновение дополнительного пьезоэлектрического заряда в буферном слое AlGaN. Показано, что использование пленок SiON с концентрацией кислорода в них более 3 % не приводит к формированию дополнительного положительного заряда, но может вызывать флуктуации тока при измерении I—V-характеристик. Рассмотрен возможный механизм транспорта носителей в области пространственного заряда, приводящий к таким флуктуациям

Influence of copper on the diffusion length of the minority carriers in devices based on n-type Si/SiO2

In the present study we demonstrate that the introduction of Cu leads to a significant reduction of the diffusion length in n-type Si/SiO2 structures. Using capacitance versus time measurements we show that the quasi-neutral generation mechanism is not dominant in Cu-contaminated samples at 90 °C. We correlate this behaviour with Cu-related defects which act as strong recombination centres in Si. Their electrical properties are determined and their origin will be discussed

Carbon-related defects in microelectronics

In the present study electrically active carbon and hydrogen-related (CH) defects, which can act as strong recombination centers in high power devices and CMOS photodetectors, are investigated in n-type Si. Several different CH-related defects are observed by using the deep level transient spectroscopy (DLTS) technique on hydrogenated Si samples with different oxygen content. The concentration of these defects is determined as low as 1012-1013 cm-3. By comparing samples with different O, C, and H concentrations the origin of the CH-related defects is derived. We show that the concentration of the electrically inactive substitutional C can be estimated by a comparison of the depth profiles of the electrically active CH-related defects in a sample with those in a reference sample which has an identical oxygen and known carbon content. This approach is applicable even for concentrations of substitutional C lower than 1015 cm-3

Carbon-hydrogen-related complexes in Si

Several deep level transient spectroscopy (DLTS) peaks (E42, E65, E75, E90, E262, and H180) are observed in n- and p-type Czochralski-grown Si samples subjected to hydrogenation by a dc H plasma treatment. The concentration of the defects is found to be proportional to the carbon and hydrogen content in our samples. The analysis of the depth profiles performed in Si samples hydrogenated by wet chemically etching shows that all these defects contain a single H atom. E65 and E75 appear only in samples with a high oxygen content which shows that oxygen is a constituent of these defects. The analysis of the enhancement of the emission rate of the defects with electric field shows that E65, E75, E90, and E262 are single acceptors whereas E42 is a double acceptor. The presence of a barrier for hole capture (about 53 meV) can explain the absence of the enhancement of the emission rate of H180, which can be attributed to a single acceptor state. From a comparison with theory, we assign E90 to CH1BC, E42 (E262) to CH1AB, and H180 to CH1Td. The similarity of the electrical properties of E65 and E75 to those of E90 suggest that E65 and E75 may originate from the CH1BC defect with an oxygen atom in its nearest neighborhood. Our results on the CH-related complexes give a conclusive explanation of some previously reported controversial experimental data