Gold and ytterbium interfacing effects on the properties of the CdSe/Yb/CdSe nanosandwiched structures

Owing to the performance of the CdSe as an optoelectronic material used for the production of quantum dots, photosensors and wave traps we here, in this article, report the enhancements in structural and electrical properties that arises from the nanosandwiching of a 40 nm thick Yb film between two films of CdSe (CYbC-40). The CdSe films which were deposited onto glass, Yb and Au substrates are characterized by X-ray diffraction, temperature dependent electrical conductivity and impedance spectroscopy measurements in the frequency range of 10–1800 MHz. The analysis of the XRD patterns have shown that the glass/CdSe/Yb/CdSe films exhibit larger grain size and lower strain, defect density and lower stacking faults compared to the not sandwiched CdSe. In addition, it was observed that the Yb shifts the donor states of the n-type CdSe from 0.44 to 0.29 eV leading to a modification in the built in voltage of the material. On the other hand, the design of the energy band diagram has shown the ability of the formation of the Au/CYbC-40/Yb as Schottky (SB) and the Au/CYbC-40/Au as back to back Schottky barriers (BBSB). While the SB device show low band pass filter characteristics, the BBSB device performed as band stop filters. The BBSB device exhibited negative capacitance effects with filtering features that reveal a return loss of 42 dB at ∼1440 MHz.     

On the reverse leakage current of Schottky contacts on free-standing GaN at high reverse biases

In this work, a dislocation-related tunneling leakage current model is developed to explain the temperature-dependent reverse current–voltage(I–V –T) characteristics of a Schottky barrier diode fabricated on free-standing GaN substrate for reverse-bias voltages up to-150 V. The model suggests that the reverse leakage current is dominated by the direct tunneling of electrons from Schottky contact metal into a continuum of states associated with conductive dislocations in GaN epilayer.A reverse leakage current ideality factor, which originates from the scattering effect at metal/GaN interface, is introduced into the model. Good agreement between the experimental data and the simulated I–V curves is obtained.     

碳纳米管薄膜晶体管中的接触电阻效应

利用不同功函数的金属作为接触电极,研究了网络状碳纳米管薄膜晶体管(CNT-TFT)的接触电阻效应。研究表明金属Pd与碳纳米管薄膜形成良好的欧姆接触, Au则形成近欧姆接触,这两种接触的器件的开态电流和迁移率较高。Ti和Al都与碳纳米管薄膜形成肖特基接触,且Al接触比Ti接触的势垒更高,接触电阻也更大,相应器件的开态电流和迁移率都较低。该结果表明对于CNT-TFT仍然可以通过接触来调控器件的性能,这对CNT-TFT的实用化进程具有重要的促进作用。     

Sulphide passivation of GaN based Schottky diodes

Wet chemical passivation of n-GaN surface was carried out by dipping GaN samples in ammonium sulphide diluted in aqueous and alcoholic solvent base solutions. Photoluminescence (PL) investigations indicated that sulphide solution effectively led to the reduction of GaN surface states. Increased band edge PL peak showed that S²⁻ ions are more active in alcohol based solvents. X-ray photoelectron spectroscopy revealed reduction in surface oxides by introduction of sulphide species. Ni/n-GaN Schottky barrier diodes were fabricated on passivated surfaces. Remarkable improvement in the Schottky barrier height (0.98 eV for passivated diodes as compared to 0.75 eV for untreated diodes) has been observed.     

Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range

The perylene(C20H12) layer effect on the electrical and dielectric properties of Al/p-Si(MS) and Al/perylene/p-Si(MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz–2 MHz. Experimental results show that C–V characteristics give an anomalous peak for two structures at low frequencies due to interface states(Nss) and series resistance(Rs). The increases in C and G/ω at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant(ε) and dielectric loss(ε) are subtracted using C and G/ω data at 1.5 V. The ε and ε values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(σac)–ln(ω) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2–V characteristics, the doping acceptor atom concentration(NA) and barrier height(ΦB) for Schottky barrier diodes(SBDs) of MS and MPS types are also obtained to be 1.484 × 1015 and 1.303 × 1015cm 3, and 1.10 and 1.13 eV, respectively.     

Experimental and numerical analyses of high voltage 4H-SiC junction barrier Schottky rectifiers with linearly graded field limiting ring

This paper describes the successful fabrication of 4H-SiC junction barrier Schottky(JBS) rectifiers with a linearly graded field limiting ring(LG-FLR). Linearly variable ring spacings for the FLR termination are applied to improve the blocking voltage by reducing the peak surface electric field at the edge termination region, which acts like a variable lateral doping profile resulting in a gradual field distribution. The experimental results demonstrate a breakdown voltage of 5 kV at the reverse leakage current density of 2 mA/cm2(about 80% of the theoretical value). Detailed numerical simulations show that the proposed termination structure provides a uniform electric field profile compared to the conventional FLR termination, which is responsible for 45% improvement in the reverse blocking voltage despite a 3.7% longer total termination length.     

Modeling of a millimeter wave planar Schottky diode using both improved equivalent circuit model and 3D-EM model

In this paper, a planar Schottky varistor diode is studied and modeled by equivalent circuit method and three dimensional full wave electromagnetic (3D-EM) method, respectively. The diode's equivalent circuit is extracted from millimeter-wave small-signal S-parameter measurements. Since the package of the diode influences the electromagnetic field distribution at millimeter and sub-millimeter wavelengths, a 3D-EM model and an improved equivalent circuit model is applied to describe the field precisely. The simulated results of equivalent circuit, improved equivalent circuit and 3D-EM model are compared with the measured results. In addition, the effects caused by silver paste conductive adhesive are considered in 3D-EM model and improved equivalent circuit model. The results show that both the 3D-EM model and improved equivalent circuit model have good S-parameter consistency with measured results.     

多脉冲直线感应加速器外接复位系统

基于硅堆隔离网络的多脉冲直线感应加速器(LIA)需要外接独立的复位系统,以满足其加速腔磁芯在主脉冲励磁前的复位需求。介绍了猝发三脉冲LIA外接复位系统的工作原理、电路参数以及具体的电路设计,并针对大型LIA感应腔数量众多、运行时电磁环境复杂的特点,介绍了复位系统在工程实施中的主要技术难点和最终布局。该复位系统解决了磁芯在励磁和复位这两种高压模式间的切换问题,实现了10~20kV可调复位电压的稳定输出,建立了在复杂电磁环境下可稳定运行的远程监控系统,确保了三脉冲LIA的92个加速腔能够在主脉冲励磁前稳定、快速、充分的复位。     

Improved GaSb surfaces using a (NH4)2S/(NH4)2S04 solution

Bulk (1 0 0) n-GaSb surfaces have been treated with a sulphur based solution ((NH₄)₂S/(NH₄)₂SO₄) to which sulphur has been added, not previously reported for the passivation of GaSb surfaces. Au/n-GaSb Schottky barrier diodes (SBDs) fabricated on the treated material show significant improvement compared to that of the similar SBDs on the as-received material as evidenced by the lower ideality factor (n), higher barrier height (?_b) and lower contact resistance obtained. Additionally, the reverse leakage current, although not saturating, has been reduced by almost an order of magnitude at −0.2 V. The sample surfaces were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The native oxide, Sb–O, present on the as-received material is effectively removed on treating with ([(NH₄)₂S/(NH₄)₂SO₄]+S) and (NH₄)₂S. Analysis of the as-received surface by XPS, prior to and after argon sputtering, suggests that the native oxide layer is ≤8.5 nm.