Effect of different type intermediate layers on band structure and gain of Ga1-xInxNyAs1-y-GaAs quantum well lasers

Based on the band-anticrossing model, the effect of the strain-compensated layer and the strain-mediated layer on the band structure, the gain, and the differential gain of GaInNAs-GaAs quantum well lasers have been investigated. Different band-filling mechanisms have been illustrated. Compared to the GaInNAs-GaAs single quantum well with the same wavelength,, the introduction. (if the strain-compensated layer and the strain-mediated layer increases the transparency carrier density. However, these multilayer structures help to suppress the degradation of the differential gain.

Valence band structures of the InAs/GaAs quantum ring

In the framework of effective-mass envelope function theory, the valence energy subbands and optical transitions of the InAs/GaAs quantum ring are calculated by using a four-band valence band model. Our model can be used to calculate the hole states of quantum wells, quantum wires, and quantum dots. The effect of finite offset and valence band mixing are taken into account. The energy levels of the hole are calculated in the different shapes of rings. Our calculations show that the effect of the difference between effective masses of holes in different materials on the valence subband structures is significant. Our theoretical results are consistent with the conclusion of the recent experimental measurements and should be useful for researching and making low-dimensional semiconductor optoelectronic devices. (C) 2002 American Institute of Physics.

Optical properties and band lineup in GaNxAs1-x/GaAs single quantum wells

The optical properties and the band lineup in GaNAs/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL) technique were investigated. It was found that the low-temperature PL is dominated by the intrinsic localized exciton emission. By fitting the experimental datawith a simple calculation, band offset of the GaN0.015As0.985/GaAs heterostructure was estimated. Moreover, DeltaE(c), the discontinuity of the conduction band was found to be a nonlinear function of the nitrogen composition (chi) and the average variation of DeltaE(c) is about 0. 110eV per % N, such smaller than that reported on the literature to (0.156 similar to 0.175 eV/N %). In addition, Qc has little change whtn N composition increares, with an experimential relation of QC approximate tox(0.25). The band bowing coefficient (b) was also studied in this paper. The measured band bowing coefficient shows a strong function of chi, giving an experimental support to the theoretic calculation of Wei Su-Huai and Zunger Alex (1996).

A 5.6-mW Power Dissipation CMOS Frequency Synthesizer for L1/L2 Dual-Band GPS Application

This paper presents a wide tuning range CMOS frequency synthesizer for dual-band GPS receiver, which has been fabricated in a standard 0.18-um RF CMOS process. With a high Q on-chip inductor, the wide-band VCO shows a tuning range from 2 to 3.6GHz to cover 2.45GHz and 3.14GHz in case of process corner or temperature variation, with a current consumption varying accordingly from 0.8mA to 0.4mA, from a 1.8V supply voltage. The measurement results show that the whole frequency synthesizer costs a very low power consumption of 5.6mW working at L I band with in-band phase noise less than -82dBc/Hz and out-of-band phase noise about -112 dBc/Hz at 1MHz offset from a 3.142GHz carrier.

A new frequency offset estimation for OFDM-based systems

A new carrier frequency offset estimation scheme in orthogonal frequency division multiplexing (OFDM) is proposed. The scheme includes coarse frequency offset estimation and fine frequency offset estimation. The coarse frequency offset estimation method we present is a improvement of Zhang's method. The estimation range of the new method is as large as the overall signal-band width. A new fine frequency offset estimation algorithm is also discussed in this paper. The new algorithm has a better performance than the Schmidl's algorithm. The system we use to calculate and simulate is based on the high rate WLAN standard adopted by the IEEE 802.11 stanidardization group. Numerical results are presented to demonstrate the performance of the proposed algorithm.

A wide-band front-end for terrestrial and cable receptions

In this paper, a wide-band low noise amplifier, two mixers and a VCO with its buffers implemented in 50GHz 0.35 mu m SiGe BiCMOS technology for dual-conversion digital TV tuner front-end is presented. The LNA and up-converting mixer utilizes current injection technology to achieve high linearity. Without using inductors, the LNA achieves 0.1-1GHz wide bandwidth and 18.8-dB gain with less than 1.4-dB gain variation. The noise figure of the LNA is less than 5dB and its 1dB compression point is -2 dBm. The IIP3 of two mixers is 25-dBm. The measurement results show that the VCO has -127.27-dBc/Hz phase noise at 1-MHz offset and a linear gain of 32.4-MHz/V between 990-MHz and 1.14-GHz. The whole chip consume 253mW power with 5-V supply.

A new frequency offset estimation for OFDM-Based systems

A-new-carrier-frequency offset estimation scheme in orthogonal frequency division multiplexing (OFDM) is proposed. The scheme includes coarse frequency offset estimation and fine frequency offset estimation. The coarse frequency offset estimation method we present is a improvement of Zhang's method. The estimation range of the new method is as large as the overall signal-band width. A new fine frequency offset estimation algorithm is also discussed in this paper. The new algorithm has a better performance than the Schmidt's algorithm. The system we use to calculate and simulate is based on the high rate WLAN standard adopted by the IEEE 802.11 standardization group. Numerical results are presented to demonstrate the performance of the proposed algorithm.

Electroluminescence behavior of ZnO/Si heterojunctions: Energy band alignment and interfacial microstructure

n-ZnO/p-Si heterojunction light-emitting diodes (LEDs) show weak defect-related electroluminescence (EL). In order to analyze the origin of the weak EL, the energy band alignment and interfacial microstructure of ZnO/Si heterojunction are investigated by x-ray photoelectron spectroscopy. The valence band offset (VBO) is determined to be 3.15 +/- 0.15 eV and conduction band offset is -0.90 +/- 0.15 eV, showing a type-II band alignment. The higher VBO means a high potential barrier for holes injected from Si into ZnO, and hence, charge carrier recombination takes place mainly on the Si side rather than the ZnO layer. It is also found that a 2.1 nm thick SiOx interfacial layer is formed at the ZnO/Si interface. The unavoidable SiOx interfacial layer provides to a large number of nonradiative centers at the ZnO/Si interface and gives rise to poor crystallinity in the ZnO films. The weak EL from the n-ZnO/p-Si LEDs can be ascribed to the high ZnO/Si VBO and existence of the SiOx interfacial layer.

Measurement of w-InN/h-BN Heterojunction Band Offsets by X-Ray Photoemission Spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) of the w-InN/h-BN heterojunction. We find that it is a type-II heterojunction with the VBO being -0.30 +/- A 0.09 eV and the corresponding conduction band offset (CBO) being 4.99 +/- A 0.09 eV. The accurate determination of VBO and CBO is important for designing the w-InN/h-BN-based electronic devices.

A Low Power Dissipation Wide-Band CMOS Frequency Synthesizer for a Dual-Band GPS Receiver

This paper presents a wide tuning range CMOS frequency synthesizer for a dual-band GPS receiver,which has been fabricated in a standard 0.18μm RF CMOS process. With a high Q on-chip inductor, the wide-band VCO shows a tuning range from 2 to 3.6GHz to cover 2.45 and 3.14GHz in case of process corner or temperature variation,with a current consumption varying accordingly from 0.8 to 0.4mA,from a 1.8V supply voltage. Measurement results show that the whole frequency synthesizer consumes very low power of 5.6mW working at L1 band with in-band phase noise less than - 82dBc/Hz and out-of-band phase noise about - ll2dBc/Hz at 1MHz offset from a 3. 142GHz carrier. The performance of the frequency synthesizer meets the requirements of GPS applications very well.

Multi-phonon gamma-vibrational bands in odd-mass nuclei studied by triaxial projected shell model approach

Inspired by the recent experimental data [J.-G. Wang, et al., Phys. Lett. B 675 (2009) 420], we extend the triaxial projected shell model approach to study the gamma-band structure in odd-mass nuclei. As a first application of the new development, the gamma-vibrational structure of Nb-103 is investigated. It is demonstrated that the model describes the ground-state band and multi-phonon gamma-vibrations quite satisfactorily, supporting the interpretation of the data as one of the few experimentally-known examples of simultaneous occurrence of one- and two-gamma-phonon vibrational bands. This generalizes the well-known concept of the surface gamma-oscillation in deformed nuclei built on the ground-state in even-even systems to gamma-bands based on quasiparticle configurations in odd-mass systems. (c) 2010 Elsevier BM. All rights reserved.

2-D and 3-D processing and interpretation of multi-fold ground penetrating radar data:a case history from an archaeological site

A 2.5-D and 3-D multi-fold GPR survey was carried out in the Archaeological Park of Aquileia (northern Italy). The primary objective of the study was the identification of targets of potential archaeological interest in an area designated by local archaeological authorities. The second geophysical objective was to test 2-D and 3-D multi-fold methods and to study localised targets of unknown shape and dimensions in hostile soil conditions. Several portions of the acquisition grid were processed in common offset (CO), common shot (CSG) and common mid point (CMP) geometry. An 8×8 m area was studied with orthogonal CMPs thus achieving a 3-D subsurface coverage with azimuthal range limited to two normal components. Coherent noise components were identified in the pre-stack domain and removed by means of FK filtering of CMP records. Stack velocities were obtained from conventional velocity analysis and azimuthal velocity analysis of 3-D pre-stack gathers. Two major discontinuities were identified in the area of study. The deeper one most probably coincides with the paleosol at the base of the layer associated with activities of man in the area in the last 2500 years. This interpretation is in agreement with the results obtained from nearby cores and excavations. The shallow discontinuity is observed in a part of the investigated area and it shows local interruptions with a linear distribution on the grid. Such interruptions may correspond to buried targets of archaeological interest. The prominent enhancement of the subsurface images obtained by means of multi-fold techniques, compared with the relatively poor quality of the conventional single-fold georadar sections, indicates that multi-fold methods are well suited for the application to high resolution studies in archaeology.

Evaluation of nonlinear chromatographic performance by frontal analysis using a simple multi-plate mathematical model

A multi-plate (NIP) mathematical model was proposed by frontal analysis to evaluate nonlinear chromatographic performance. One of its advantages is that the parameters may be easily calculated from experimental data. Moreover, there is a good correlation between it and the equilibrium-dispersive (E-D) or Thomas models. This shows that it can well accommodate both types of band broadening that is comprised of either diffusion-dominated processes or kinetic sorption processes. The MP model can well describe experimental breakthrough curves that were obtained from membrane affinity chromatography and column reversed-phase liquid chromatography. Furthermore, the coefficients of mass transfer may be calculated according to the relationship between the MP model and the E-D or Thomas models. (C) 2004 Elsevier B.V. All rights reserved.

Copper phthalocyanine on InSb(111)A?interface bonding, growth mode and energy band alignment

Copper phthalocyanine on InSb(111)A?interface bonding, growth mode and energy band alignment, D.A. Evans, H.J. Steiner, S. Evans, R. Middleton, T.S. Jones, S. Park, T.U. Kampen, D.R.T. Zahn, G. Cabailh and I.T. McGovern, J. Phys.: Condens. Matter, 15, S2729?S2740, (2003)

Space-borne study of seasonal, multi-year, and decadal phytoplankton dynamics in the Bay of Biscay

Seasonal and inter-annual variations in phytoplankton community abundance in the Bay of Biscay are studied. Preliminarily processed by the National Aeronautics and Space Administration (NASA) to yield normalized water-leaving radiance and the top-of-the-atmosphere solar radiance, Sea-viewing Wide Field-of-View Sensor (SeaWiFS), Moderate Resolution Imaging Spectroradiometer (MODIS), and Coastal Zone Color Scanner (CZCS) data are further supplied to our dedicated retrieval algorithms to infer the sought for parameters. By applying the National Oceanic and Atmospheric Administration's (NOAA's) Advanced Very High Resolution Radiometer (AVHRR) data, the surface reflection coefficient in the only band in the visible spectrum is derived and employed for analysis. Decadal bridged time series of variations of diatom-dominated phytoplankton and green dinoflagellate Lepidodinium chlorophorum within the shelf zone and the coccolithophore Emiliania huxleyi in the pelagic area of the Bay are documented and analysed in terms of impacts of some biogeochemical and geophysical forcing factors.