Spin effects in magnetoresistance induced in an <Emphasis Type="Italic">n</Emphasis>-In<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs double quantum well by a parallel magnetic field

Magnetoresistance in n-In_xGa_1?xAs/GaAs (x ≈ 0.18) heterostructures with double quantum wells (DQWs) was studied in the magnetic field parallel to the DQW layer. Specific features of the magnetoresistance, related to the passing of the tunnel gap edges across the Fermi level, are revealed and studied. Agreement between the calculated and experimental positions of the observed features is obtained when the spin splitting of the energy spectrum is taken into account. Earlier, similar features were observed in the magnetoresistance of n-GaAs/Al_xGa_1?xAs DQW heterostructures, but the spin effects did not manifest themselves.     

Thermal-field forward current in GaN-based surface-barrier structures

The voltage and temperature dependences of the capacitance and forward current in surface-barrier Ni-n-GaN structures are experimentally studied. The results are compared with the Padovani-Stratton thermofield emission theory. It is established that, in a temperature range of 250–410 K, the forward current of the Ni-n-GaN surface-barrier structures (the electron density in GaN is ～10¹⁷ cm^?3) is caused by a thermofield emission of electrons, whose energy is ～0.1 eV below the potential-barrier top.     

Bloch oscillations in superlattices: The problem of a terahertz oscillator

The feasibility of designing a terahertz oscillator based on the Bloch oscillations of electrons in semiconductor superlattices is studied. It is shown that superlattices with high-Q Bloch oscillations can be used to generate a terahertz emission in pulsed electric fields with an off-duty factor that ensures the thermalization of electrons heated by the field. It is suggested that a terahertz oscillator is designed with a frequency that is tuned continuously by an electric field on the basis of anharmonic Bloch oscillations of electrons in semiconductor superlattices that have special miniband characteristics in which the major part of the effective electron mass is positive and increases as the electron energy increases. This circumstance makes it possible to eliminate the development of undesired domain instability (the Gunn effect).     

Spatial-resolution enhancement in computed tomography

We propose an approach that combines an asymmetric fan-beam configuration and a new reconstruction algorithm to enhancing spatial resolution in computed tomography (CT). The asymmetric configuration can be achieved by changing the center of rotation (COR) from the conventional symmetric configuration. It does not, however, require new detectors and X-ray source nor alter the relative geometry between the detector and the X-ray source. By effectively reducing the distance of the COR to the X-ray source, the asymmetric configuration can increase the effective sampling density in projection data without reducing the size of the field of view (FOV). The proposed algorithm, on the other hand, can reconstruct images directly from data acquired with this asymmetric configuration. We performed numerical studies to demonstrate and validate the proposed acquisition/reconstruction approach. Results in these studies confirm that the proposed approach can lead to enhanced spatial resolution in reconstructed images. The proposed acquisition/reconstruction approach may find applications in micro-CT and industrial CT in which the CORs may be changed.     

可信计算环境下基于进化理论的层信任模型实现

本文采用形式化的方法,借鉴和吸收生物学、经济学、社会科学等相关学科的理论,对可信计算进行深入分析,并进行严格的逻辑推理证明,提出了基于进化理论的层信任模型。该模型在逻辑结构上定义了可信计算环境基本的信任链和可信层,物理结构上通过广电网的基于法定权利义务关系的可信根广播和在可信终端建立基于可信存储的可信根来实现可信计算环境。该模型使得现有通用计算平台也适用于可信计算环境,提出了解决可信计算环境的外部性和公正性的方法,减少了可信终端主动防御带来的验证开销,用较小的代价实现了可信计算环境下可信计算实体的可信度收敛。     

基于Credence Gemini500的内嵌式AD转换器测试方法研究

本文中应用Credence公司的Gemini500测试系统对某一SoC芯片内嵌模数转换器进行了测试。根据芯片功能分析和封装形式,对测试板进行了优化设计。根据内嵌式ADC的时序特点进行了测试向量的设计。     

Stress Mechanism about Field Lightning Surge of High Voltage BJT Based Line Driver for ADSL System

In this paper, we have verified stress root caused by lightning surge in High voltage BJT based line driver of ADSL telecommunication and created failure mechanism. To reproduce damages in Line driver, we have applied STD surge waveform in operating condition, which is specified in IEC-6000-4-5, to component and board level. Visual isolation for Damage root was conducted with Real-time Electrical Stress Analysis (RTESA) utilizing Photon Emission Microscopy (PEM). The surge made with input of Tx output created junction breakdown of amplifier, which is made of HVBJT cells, and also caused current crowding from Vcc (supply voltage). In case of Positive pulse, current crowding was observed from between Collector and Vcc (+)12V. For negative pulse, at between Emitter and Vee (−)12V, current crowding was found. For both cases, device damage level was the same. All of these could be considered as transient latchup phenomenon created in BJT cell. Applying temporary clamping diode to line driver Tx, we have conducted Board level surge injection test. As a result, with the correlation between surge level from component level reproduction test and the one from system level, we have decided field lightning surge damage level and set up line driver protection margin.     

Electrically Conductive Carbon-Nanotube Framework Materials

Semiconductors - Conductive materials based on carbon and its modifications are most promising for creating biointerfaces. Such materials can be used for the targeted stimulation of cells and...     

Optical constants of silicon nanoparticle thin films grown by laser electrodispersion

The study of films consisting of amorphous close-packed silicon nanoparticles grown by laser electrodispersion is continued. The optical transmission and reflection spectra of films fabricated in vacuum and at various pressures of oxygen introduced into the chamber to passivate the nanoparticle surface are measured. The spectra of the refractive index and extinction coefficient are calculated. The shape of the spectra of the optical constants correlates with that of the spectra of bulk amorphous silicon; however, the values obtained differ from the parameters of bulk amorphous silicon. The differences are caused by the significant volume of voids between nanoparticles and a large number of dangling bonds (defects) on the nanoparticle surface. The optical constants decrease with increasing oxygen content in the films, which is indicative of the passivation of dangling bonds by oxygen.     

Influence of temperature on the mechanism of carrier injection in light-emitting diodes based on InGaN/GaN multiple quantum wells

The experimental current-voltage characteristics and dependences of the external quantum yield on the current density of light-emitting diodes based on InGaN/GaN multiple quantum wells for the wide temperature range T = 10–400 K are presented. It is shown that, at low-temperatures T < 100 K, the injection of holes into the quantum wells occurs from localized acceptor states. The low-temperature injection of electrons into p-GaN occurs due to quasi-ballistic transport in the region of multiple quantum wells. An increase in temperature leads to an increase in the current which is governed by thermally activated hole and electron injection from the allowed bands of GaN.