Characterization of germanium implanted Si1−xGex layer

Characterization of a Si_1−xGe_x layer formed by high-dose germanium implantation and subsequent solid phase epitaxy is reported. Properties of this layer are obtained from electrical measurements on diodes and transistors fabricated in this layer. Results are compared with those of the silicon control devices. It was observed that the germanium implantation created considerable defects that are difficult to eliminate with annealing. These defects result in boron deactivation in the p-type regions of the devices, giving rise to larger resistance. Optimization of the device structure and fabrication process is discussed.     

Impurity study of CdZnTe substrates used for LPE HgCdTe

Impurites were tracked from raw material purification through to CdZnTe processing in an effort to identify the sources of elements which impact on IR photodetector performance. Chemical analyses by GDMS and ZCGFAA effectively showed the levels of impurities introduced into CdZnTe substrate material from the manufacturing processes. A new purification process (ISDZR) for raw materials was developed, resulting in improved CdZnTe substrate purity. Substrate CU contamination was found to have detrimental effects on LPE layer and device electrical properties for lightly doped HgCdTe.     

Analysis of leaky bucket mechanism based on burstiness characterization

In high-speed networks, a congestion control strategy has to manage bandwidth allocation based on the characteristics of input traffic sources. Accordingly, the definition of traffic characterization becomes significant in all aspects concerning network performance. In this paper, the burstiness characterization of a traffic stream is based on a virtual queue principle. We study the leaky bucket mechanism as a regulator element that controls input traffic before access to a newwork, as well as inside a network. To protect an input traffic stream, we investigate the optimal parameter settings of a leaky bucket. In addition, we analyse the worst case performance, and obtain upper bounds on loss probability and packet delay. We also determine the characteristics of an output stream in the worst case. Such performance bounds reveal the effectiveness of a leaky bucket, and provide enough information for the QOS satisfaction of the network users.     

Experimental and theoretical investigation of defects at (1 0 0) Si1−xGex/oxide interfaces

The identification of a nontrigonal Ge dangling bond at SiO₂/Si_1−xGe_x/SiO₂ heterostructures and its electrical activity are discussed, both from experimental and theoretical points of view. This dangling bond is observed from multifrequency electron-spin resonance experiments performed at 4.2 K, for typical Ge concentrations in the range 0.4 ≤ x ≤ 0.85. The electrical activity of this defect is revealed from capacitance-voltage characteristics measured at 300 and 77 K, and is found to behave like an acceptor defect. First-principles calculations of the electronic properties of this Ge dangling bond indicate that its energy level approaches the valence band edge of the Si_1−xGe_x layer as the Ge content increases, confirming its acceptor-like nature.     

New techniques in SIMS analysis of HgCdTe materials

This paper presents two new approaches used in the secondary ion mass spectrometry (SIMS) for high sensitivity dopant and impurity analysis in HgCdTe materials, namely, the high mass resolution with dynamic transfer and the MCs⁺ technique. It is shown that better detection limits for As and Cu can be obtained at a level of 2–5e14 at/cm³. The MCs⁺ technique has added advantages of better measurement precision, monitoring Cd composition in the same profile, and small device area analysis capability. Advantages and trade-offs of each technique are discussed and compared. An updated detection limit table for all elements measured in HgCdTe materials using SIMS is also presented.     

Characterization of amorphous Ni-Si binary alloy films by flash evaporation

We previously reported on an extremely small temperature coefficient of resistivity (TCR) of thin amorphous Ni-Si film resistors fabricated by new flash evaporating method, which have a wide range of resistivity.¹ In the present paper, we describe the structural and chemical properties of these films for the purpose of clarifying the cause of resistive change of films resulting from heat treatment. X-ray diffraction patterns show that Ni-Si films with greater than 20 wt.% Si remains predominantly amorphous after heat treatment. Changes in composition and binding energy of the films resulting from heat treatment are measured by means of XPS. Electrical characteristics are also investigated as a function of Si concentration and temperature. The resistance variations resulting from heat treatment are found to originate from a structural change. The activation energy needed for this change is obtained by analyzing the extent of change during isothermal heating and found to vary from 1 eV to 2.5 eV with increasing Si content from 20 wt.% to 80 wt.%.     

Micro-Raman characterization of Germanium thin films evaporated on various substrates

We perform an extensive micro-Raman analysis of Germanium thin films physically evaporated on several substrates including silicon, silicon oxide and glass. We investigate the dependence of crystal quality on thin film deposition parameters such as substrate temperature and growth rate. We also study the continuous transitional change of the material structure from amorphous to crystalline phases. Ge films obtained by this simple and low cost technique are a viable solution towards the realization of virtual substrates and devices.     

Spectral study and classification of worldwide locations considering several multijunction solar cell technologies

Multi‐junction solar cells are widely used in high‐concentration photovoltaic systems (HCPV) attaining the highest efficiencies in photovoltaic energy generation. This technology is more dependent on the spectral variations of the impinging Direct Normal Irradiance (DNI) than conventional photovoltaics based on silicon solar cells and consequently demands a deeper knowledge of the solar resource characteristics. This article explores the capabilities of spectral indexes, namely, spectral matching ratios (SMR), to spectrally characterize the annual irradiation reaching a particular location on the Earth and to provide the necessary information for the spectral optimization of a MJ solar cell in that location as a starting point for CPV module spectral tuning. Additionally, the relationship between such indexes and the atmosphere parameters, such as the aerosol optical depth (AOD), precipitable water (PW), and air mass (AM), is discussed using radiative transfer models such as SMARTS to generate the spectrally resolved DNI. The network of ground‐based sun and sky‐scanning radiometers AErosol RObotic NETwork (AERONET) is exploited to obtain the atmosphere parameters for a selected bunch of 34 sites worldwide. Finally, the SMR indexes are obtained for every location, and a comparative analysis is carried out for four architectures of triple junction solar cells, covering both lattice match and metamorphic technologies. The differences found among cell technologies are much less significant than among locations. Copyright © 2016 John Wiley & Sons, Ltd.     

Spectrum‐Based Color Reproduction Algorithm for Makeup Simulation of 3D Facial Avatar

Various simulation applications for hair, clothing, and makeup of a 3D avatar can provide more useful information to users before they select a hairstyle, clothes, or cosmetics. To enhance their reality, the shapes, textures, and colors of the avatars should be similar to those found in the real world. For a more realistic 3D avatar color reproduction, this paper proposes a spectrum‐based color reproduction algorithm and color management process with respect to the implementation of the algorithm. First, a makeup color reproduction model is estimated by analyzing the measured spectral reflectance of the skin samples before and after applying the makeup. To implement the model for a makeup simulation system, the color management process controls all color information of the 3D facial avatar during the 3D scanning, modeling, and rendering stages. During 3D scanning with a multicamera system, spectrum‐based camera calibration and characterization are performed to estimate the spectrum data. During the virtual makeup process, the spectrum data of the 3D facial avatar is modified based on the makeup color reproduction model. Finally, during 3D rendering, the estimated spectrum is converted into RGB data through gamut mapping and display characterization.     

Seeded growth of AlN crystals on nonpolar seeds via physical vapor transport

Seeded growth of AlN single crystals was demonstrated in an induction-heated, high-temperature reactor via a physical vapor transport (PVT) process. AlN seeds were prepared from a self-seeded boule containing large single-crystalline grains. Seeded growth was interrupted several times in order to refill the AlN powder source, and a dedicated process scheme was used to ensure epitaxial growth on the seed surface, after prior exposure to air. The growth temperatures were in the range of 2200–2300°C, and the reactor pressure was in the range of 500–900 torr of UHP-grade nitrogen during each growth run. Under these growth conditions, a seed (10 mm diameter) expanded at an angle of 45°, and a larger single crystal up to 18 mm in diameter was obtained. The as-grown surface had three facets, of which facet (1120) was smooth and featureless while the other two, (4150) and (2570), showed serrated morphologies. The double-crystal x-ray rocking curve and glow discharge mass spectroscopy analysis confirmed that the grown crystal was of high crystalline quality with low impurity incorporation.