Numerical analysis of a DAR IMPATT diode

The analysis and optimization of the n ⁺ pvnp ⁺ avalanche diode structure that includes two avalanche regions have been realized on basis of the nonlinear model and special optimization procedure. The admittance and energy characteristics of the DAR diode were analyzed in very wide frequency band from 30 up to 360 GHz. Output power level was optimized for the second frequency band near the 220 GHz.     

Metastable He deexcitation at semiconductor interfaces

A review is given of the application of metastable deexcitation spectroscopy (MDS) to the study of the interface formation between semiconductors and different materials. In particular we present an overview of the results obtained on nanostructured interfaces, where strain and reaction between the substrate and the overlayer atoms drive the growth mode and the morphology of the system. As prototypical examples we discuss the growth of CaF₂ on silicon and rare earths (Yb, Er) on silicon and gallium arsenide. The mechanisms and chemical reactions which bring to interface formation are examined on the basis of MDS results and their comparison with photoemission.     

半导体材料少子寿命测试仪的研制开发

少数载流子寿命(简称少子寿命)是半导体材料的一项重要参数，它对半导体器件的性能、太阳能电池的效率都有重要的影响。我们采用微波反射光电导衰减法研制了一台半导体材料少子寿命测试仪，本文将对测试仪的实验装置、测试原理及程序计算进行了较详细的介绍，并与国外同类产品的测试进行比较，结果表明本测试仪测试结果准确、重复性高，适合少子寿命的实验室研究和工业在线测试。     

p型透明导电氧化物薄膜的研究进展

p型透明导电膜是近来发现的一种新型的材料,在透明有源器件、传感器、透明电极和电路等方面具有广泛的潜在应用.近来在这方面的研究取得了一些突出的进展.本文主要综述了关于p型透明导电膜在材料、沉积工艺以及相关器件方面的研究进展.     

First principles total energy studies of the adsorption of germane on Ge(001)-c(2 × 4)

We perform first principles total energy calculations to study the energetics, and the atomic structure of the adsorption of germane (GeH₄) molecules on the Ge(001)-c(2 × 4) surface. The adsorption of a GeH₄ unit occurs after its dissociation into a germanium trihydride (GeH₃) and a hydrogen atom and a subsequent decomposition into a germanium dihydride (GeH₂) subunit and H atoms. Consequently, we first consider the adsorption of GeH₂ in two different configurations; the on-dimer and the intra-row geometries. Similar to the adsorption of SiH₂ and GeH₂ on Si(001), it is found that the on-dimer site is more stable than the intra-row geometry by 0.13 eV. However, in the adsorption of a GeH₂ fragment together with two H atoms we find that the intra-row geometry is energetically more favorable, again, similar to the adsorption of SiH₂ and GeH₂ (plus two H atoms) on the Si(001) surface.     

Study of TiN/BN bilayers produced by pulsed arc plasma

Bilayers of TiN/BN were produced by using a PAPVD (Plasma Assisted Physical Vapor Deposition) pulsed vacuum arc system. The equipment is formed by a reactor composed by a vacuum chamber with two face-to-face electrodes and an RLC circuit to produce the arc discharge. To obtain the BN coating a target of h-BN was used placed on the cathode and a substrates of silicon placed on the anode. The work gas was nitrogen at a pressure of 4.4×10⁻¹ mbar and a voltage of 240 V. In order to improve the adherence of the BN film, an interlayer of TiN was grown. In this case the chamber was filled with N₂ to produce the TiN coating, with a pressure of 1.7 mbar and a voltage of 300 V. By means of XRD (X-ray diffraction), the existence of TiN was determined finding different crystalline orientation in FCC phase. An FTIR (Fourier Transform Infrared Spectroscopy) was employed to determine sp³/sp² bonding ratio in the BN film.By plotting I-V curves the electrical properties of the bilayer were studied, observing a semiconductor behavior and this result was compared to the silicon substrate without coating.     

High aspect ratio CdS nanowires synthesized in microemulsion system

CdS nanowires with typical length more than 8 μm and width of 30 nm on average have been successfully synthesized through Cd(NO₃)₂ reacting with CS₂ and ethylenediamine in microemulsion system of sodium dodecylbenzene sulfonate (SBDS). The microstructures of the as-synthesized CdS nanowires were characterized using XRD, transmission electron microscopy (TEM) and HRTEM. The possible formation mechanism was discussed. The morphologies of CdS sample strongly depend on the concentration of surfactant in solutions.     

Ionic liquid assisted sonochemical synthesis of NiS submicron particles

A novel synthesis methodology is reported for the preparation of NiS submicron particles in a green solvent 1-butyl-3methylimidazolium tetrafluoroborate (BMImBF₄) ionic liquid (IL), using ultrasonic sonochemical technique. Structural, morphological and optical properties of nickel sulfide powders were obtained by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). Composition was corroborated by energy dispersive X-ray spectroscopy (EDXS), both in the SEM and in the TEM. Regular shape particles were obtained under high-intensity ultrasonic irradiation for 105 min from the reaction between nickel nitrate and thioacetamide in ethanol/BMImBF₄ (80:20), respectively. After vacuum annealing treatment at 180 °C overnight, spherical crystalline NiS particles were observed. The powders showed a band gap of 0.74 eV.     

Semiconductor supply planning by considering transit options to take advantage of pre-productions and order cancellations

One of the objectives of supply planning is to find when and how many productions have to be started to minimize total cost. We aim to find the optimum. Base data like the length of transit time are important parameters to plan for the optimum start of production. In this research, we considered two kinds of transit options: normal transit and emergency transit, and we distinguished between planned and executed transit. The decision regarding which transit option to choose for the execution is trivial because emergency is only used when it is needed since normal transit is more cost efficient. However, for planning purpose, it is more difficult to decide which transit option should be used since the uncertainty in demand and supply between plan and execution can allow to plan an emergency transit but to execute the delivery with normal transit, which is a huge benefit in the competitive capital intensive semiconductor industry. If we planned an emergency, we can save inventory and production cost as we can delay the start of production. In contrast, we need pay additional transit cost in case that emergency transit is actually executed. Many characteristics of the semiconductor industry, which might be the front runner for many other industries, are considered in this model such as demand uncertainty, supply uncertainty and economic volatility. In our numerical experiments, we could gain the optimum, depending on each economic situation. Furthermore, we conducted sensitivity analysis of the effect of demand and supply uncertainties on total cost.     

Photoluminescence and X-ray luminescence of Pb0.30Cd0.70I2 solid solutions. Comparative study

The nature and relative contributions (RCs) of various radiative recombination processes to the photoluminescence (PL) spectra for bulk nanostructured Pb_0.30Cd_0.70I₂ solid solutions have been established at different temperatures. The analysis indicates that the PL is caused by free, bound and self-trapped excitons as well as by donor-acceptor pairs emission with the participation of shallow and deep acceptor centers. It was shown that X-ray luminescence (XRL) spectra are also determined by these recombination processes. However, their RC and the temperature evolution are considerably different. Besides, XRL spectra contain an intense long-wavelength band associated with the emission of many LO-phonons. It was shown that the deep luminescence surface states, associated with the self-trapped excitons and deep intrinsic defects, mainly determine the intensity of XRL spectra both at 80 K and room temperature. The results obtained open the way to the optimization of the scintillator properties of the investigated materials.