GaSb and InAs: New Materials for Metal-Semiconductor Point-Contact Diodes

Metal-semiconductor point contact diodes have proved to be good detectors and mixers for radiation from the far-infrared to visible. Until now GaAs, InSb and InP are the most studied and used semiconductor materials for these devices. In this work we present the performance in the visible and infrared region for metal-semiconductor point-contact diodes with GaSb or InAs as the semiconductor layers. These two new materials have shown good characteristics.     

怎样为应用选择最佳的控制技术

您是否曾经在一个糖果店门口止步,面对成千上百不同颜色、口味和形状的糖果不知所措.当处理开关电源设计,面对如何选择最合适的控制技术时,您也会遭遇同样的境况.     

Optimal design of Service Overlay Networks with economic and performance constraints

In the last years, Service Overlay Networks (SONs) have emerged as a promising means to address some of the issues (e.g. end‐to‐end QoS) affecting the current Internet and to favor the development and deployment of new value‐added Internet services. The deployment of an SON is a capital‐intensive investment, since bandwidth with certain QoS guarantees must be purchased from the individual network domains through bilateral Service Level Agreements. Thus, minimizing the economic cost of the logical end‐to‐end service delivery infrastructure is one of the key objectives for the SON provider. When a SON is aimed at end‐to‐end QoS provisioning, its topology must be designed so as to also satisfy the specific requirements of QoS‐sensitive applications. This paper deals with the problem of planning the SON topology in order to take into account both cost and QoS constraints. More specifically, the paper proposes a set of new algorithms for the design of an optimized SON topology, which minimizes the economic cost while simultaneously meeting bandwidth and delay constraints. A performance comparison among such algorithms is finally carried out. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,size-dependent optoelectronic and charge transport properties of thieno(bis)imide end-substituted molecular semiconductors

The synthesis of two new thieno(bis)imide (TBI, N) end functionalized oligothiophene semiconductors is reported. In particular, trimer (NT3N) and pentamer (NT5N) have been synthesized and characterized. Two different synthetic approaches for their preparation were tested and compared namely conventional Stille cross coupling and direct arylation reaction via C–H activation. Theoretical calculations, optical and electrochemical characterization allowed us to assess the role of the π-conjugation extent, i.e., of the oligomer size on the optoelectronic properties of these materials. In both TBI ended compounds, due to the strong localization of the LUMO orbital on the TBI unit, the LUMO energy is almost insensitive to the oligomer size, this being crucial for the fine-tailoring of the energy and the distribution of the frontier orbitals. Surprisingly, despite its short size and contrarily to comparable TBI-free analogues, NT3N shows electron charge transport with mobility up to μ_N = 10⁻⁴ cm² V⁻¹ s⁻¹, while increasing the oligomer size to NT5N promotes ambipolar behavior and electroluminescence properties with mobility up to μ_N = 0.14 cm² V⁻¹ s⁻¹ and to μ_P = 10⁻⁵ cm² V⁻¹ s⁻¹.     

FIR Laser Lines from CH3OD: A Review

The methanol isotopic species CH₃OD has also proved to be an efficient and powerful medium to generate radiation in the far infrared (FIR) region. After the critical review of 1994, six papers have been published dealing with new FIR laser lines from this molecule. As a consequence of the use of wide tunability waveguide CO₂ lasers as well as a new pulsed CO₂ laser operating at hot and sequential bands, as of optical pumping sources, the total number of the FIR laser lines increased from 122 in 1994 to 227 today. In this communication we present an updated and complete catalogue of FIR laser lines generated from CH₃OD. Information on wavelength, offset, relative polarization, intensity, and optimum operation pressure is generally available.     

Filtering for bimodal systems: the case of unknown switching statistics

This paper considers the problem of state estimation for discrete-time systems whose dynamics randomly switches between two linear stochastic behaviors (bimodal systems). The novelty of this paper is that no statistical information on the switching process is assumed available for the filter design. Two different approaches are here proposed to solve the estimation problem in these conditions. One method is based on a combined use of stochastic singular systems and of the minimax filtering theory, while the other relies on the maximum entropy principle. Based on these approaches two filtering algorithms are derived, whose features are theoretically and numerically compared. Some attention has been devoted to the study of the asymptotic properties of both the filters.     

Dynamic utility and price based radio resource management for rate adaptive traffic

This paper explores analytical Radio Resource Management models where the relationship between users and services is mapped through utility functions. Compared to other applications of these models to networking, we focus in particular on specific aspects of multimedia systems with adaptive traffic, and propose a novel framework for describing and investigating dynamic allocation of resources in wireless networks. In doing so, we also consider economic aspects, such as the financial needs of the provider and the users’ reaction to prices. As an example of how our analytical tool can be used, in this paper we compare different classes of RRM strategies, e.g., Best Effort vs. Guaranteed Performance, for which we explore the relationships between Radio Resource Allocation, pricing, provider’s revenue, network capacity and users’ satisfaction. Finally, we present a discussion about Economic Admission Control, which can be applied in Best Effort scenarios to further improve the performance. Part of this work has been presented at the conference ACM/IEEE MSWiM 2004, Venice (Italy). Leonardo Badia received a Laurea degree (with honors) in electrical engineering and a Ph.D. in information engineering from the University of Ferrara, Italy, in 2000 and 2004, respectively. He was a Research Fellow at the University of Ferrara from 2001 to 2006. During these years, he also had collaborations with the University of Padova, Italy, and Wireless@KTH, Royal Institute of Technology, Stockholm, Sweden. In 2006, he joined the “Institutions Markets Technologies” (IMT) Institute for Advanced Studies, Lucca, Italy, where he is currently a Research Fellow. His research interests include wireless ad hoc and mesh networks, analysis of transmission protocols, optimization tools and economic models applied to radio resource management. Michele Zorzi received a Laurea degree and a Ph.D. in electrical engineering from the University of Padova in 1990 and 1994, respectively. During academic year 1992–1993, he was on leave at UCSD, attending graduate courses and doing research on multiple access in mobile radio networks. In 1993 he joined the faculty of the Dipartimento di Elettronica e Informazione, Politecnico di Milano, Italy. After spending three years with the Center for Wireless Communications at UCSD, in 1998 he joined the School of Engineering of the University of Ferrara, Italy, where he became a professor in 2000. Since November 2003 he has been on the faculty at the Information Engineering Department of the University of Padova. His present research interests include performance evaluation in mobile communications systems, random access in mobile radio networks, ad hoc and sensor networks, energy constrained communications protocols, and broadband wireless access. He was Editor-In-Chief of IEEE Wireless Communications, 2003–2005, and currently serves on the Editorial Boards of IEEE Transactions on Communications, IEEE Transactions on Wireless Communications, Wiley’s Journal of Wireless Communications and Mobile Computing, and ACM/URSI/Kluwer Journal of Wireless Networks, and on the Steering Committee of the IEEE Transactions on Mobile Computing. He has also been a Guest Editor of special issues in IEEE Personal Communications (Energy Management in Personal Communications Systems) and IEEE Journal on Selected Areas in Communications (Multimedia Network Radios).     

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Buried‐channel semiconductor heterostructures are an archetype material platform for the fabrication of gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface; however, nearby surface states degrade the electrical properties of the starting material. Here, a 2D hole gas of high mobility (5 × 10⁵ cm² V^?1 s^?1) is demonstrated in a very shallow strained germanium (Ge) channel, which is located only 22 nm below the surface. The top‐gate of a dopant‐less field effect transistor controls the channel carrier density confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The high mobility leads to mean free paths ≈ 6 µm, setting new benchmarks for holes in shallow field effect transistors. The high mobility, along with a percolation density of 1.2 × 10¹¹cm^?2, light effective mass (0.09m_e), and high effective g‐factor (up to 9.2) highlight the potential of undoped Ge/SiGe as a low‐disorder material platform for hybrid quantum technologies.     

A 2D Full-Band Monte Carlo Study of HgCdTe-Based Avalanche Photodiodes

This work presents a numerical simulation study of HgCdTe-based avalanche photodetectors (APDs). The two-dimensional model used is based on a full-band Monte Carlo approach in which the electronic structure is computed using a nonlocal empirical pseudopotential model with spin–orbit corrections. The carrier–phonon scattering rates have been computed from first principles using a rigid pseudo-ion model. The most attractive feature of these devices is the potential for single-carrier ionization when electrons are used as the primary injection carrier. For this reason, this work focuses on two front-illuminated (electron-injection) device structures: a planar diffused PIN structure and a planar diffused PN photodiode with guard rings. To predict the performance of these APDs, the electron multiplication gain has been studied as a function of the position where photogenerated carriers are injected and as a function of the curvature of the p-type diffusion region. We find that, in the diffused PIN structure, the limited lateral spatial extent of the high-electric-field region leads to a reduction of the multiplication gain from the center of the device to the periphery. Furthermore, the higher the curvature, the more abruptly the gain decreases. For the simple PN structure, we find that the presence of the guard rings removes the high electric field from the surface and induces a more gradual roll-off of the gain from the center of the device to the periphery.