Homoepitaxial growth and device characteristics of SiC on Si-face (0001) 6H-SiC

Homoepitaxial growth of SiC on a Si-face (0 0 0 1) GH-SIC substrate has been performed in a modified gas-source molecular beam epitaxy system with Si2H6 and C2H4 at temperatures ranging 1000 1450 degreesC while keeping a constant SiC ratio (0.7) in the gas phase. X-ray diffraction patterns, Raman scattering measurements. and low-temperature photoluminescence spectra showed single-crystalline SiC. Mesa-type SiC p-n junctions were obtained on these epitaxial layers, and their I-V characteristics are presented. (C) 2001 Elsevier Science B.V. All rights reserved.

Modification of emission wavelength of self-assembled In(Ga)As/GaAs quantum dots covered by InxGa1-xAs(0 <= x <= 0.3) layer

Red shifts of emission wavelength of self-organized In(Cla)As/GaAs quantum dots (QDs) covered by 3 nm thick InxGa1-xAs layer with three different In mole fractions (x = 0.1, 0.2 and 0.3, respectively) have been observed. Transmission electron microscopy images demonstrate that the stress along growth direction in the InAs dots was reduced due to introducing the InxGa1-xAs (x = 0.1, 0.2 and 0.3) covering layer instead of GaAs layer. Atomic force microscopy pictures show a smoother surface of InAs islands covered by an In0.2Ga0.8As layer. It is explained by the calculations that the redshifts of the photoluminescence (PL) spectra from the QDs covered by the InxGa1-xAs (x greater than or equal to 0.1) layers were mainly due to the reducing of the strain other than the InAs/GaAs intermixing in the InAs QDs. The temperature dependent PL spectra further confirm that the InGaAs covering layer can effectively suppress the temperature sensitivity of PL emissions. 1.3 mum emission wavelength with a very narrow linewidth of 19.2 mcV at room temperature has been obtained successfully from In,In0.5Ga0.5As/GaAs self-assembled QDs covered by a 3-nm In0.2Ga0.2As strain reducing layer. (C) 2001 Elsevier Science B.V. All rights reserved.

Optical properties of self-assembled ternary In(GA/Al)As quantum dots on (100) and (N 1 1)B InP substrates

In this paper, we investigated the self-assembled quantum dots formed on (100) and (N11)B (N = 2, 3, 4, 5) InP substrates by molecular beam epitaxy (MBE). Two kinds of ternary QDs (In0.9Ga0.1As and In0.9Al0.1As QDs) are grown on the above substrates; Transmission electron microscopy (TEM) and photoluminescence (PL) results confirm QDs formation for all samples. The PL spectra reveal obvious differences in integral luminescence, peak position, full-width at half-maximum and peak shape between different oriented surfaces. Highest PL integral intensity is observed from QDs on (411)B surfaces, which shows a potential for improving the optical properties of QDs by using high-index surface. (C) 2000 Elsevier Science B.V. All rights reserved.

Structural and photoluminescence properties of In-0.9(Ga/Al)(0.1)As self-assembled quantum dots on InP substrate

Self-assembled In0.9Ga0.1As, In0.9Al0.1As, and InAs quantum dots (QD) were fabricated in an InAlAs matrix lattice-matched to an InP substrate by molecular beam epitaxy. Preliminary characterizations were performed using transmission electron microscopy, photoluminescence, and reflection high-energy electron diffraction. Experimental results reveal clear differences in QD formation, size distribution, and luminescence between the InAs and In-0.9(Ga/Al)(0.1)As samples, which show the potential of introducing ternary compositions to adjust the structural and optical properties of QDs on an InP substrate. (C) 2000 American Institute of Physics. [S0021-8979(00)10213-0].

Tuning of conduction intersublevel absorption wavelengths in (In, Ga)As/GaAs quantum-dot nanostructures

We demonstrate that by increasing the amount of (In, Ga)As deposit in a quantum dot layer, the intersublevel absorption wavelength for (In, Ga)As/GaAs quantum-dot infrared photodetectors can be blue-shifted from 15 to 10 mu m while the photoluminescence peak is red-shifted. We directly compare the measured energy spacing between intersublevels obtained from infrared absorption spectroscopy with those obtained from photoluminescence spectroscopy. We find that the intersublevel energy spacing determined from absorption measurements is much larger than that obtained from the photoluminescence measurements. (C) 2000 American Institute of Physics. [S0003-6951(00)04524-1].

Strain and photoluminescence characterization of cubic (In,Ga)N films grown on GaAs(001) substrates

Cubic InxGa1-xN films were successfully grown on GaAs(001) substrates by metalorganic chemical-vapor deposition. The values of x content ranging from 0.10 to 0.24 obtained at different growth conditions were measured by double-crystal x-ray diffraction (XRD). The perpendicular and parallel elastic strain of the In0.2Ga0.8N layer, epsilon(perpendicular to)=0.4% and epsilon(parallel to)=-0.4% for GaN and epsilon(perpendicular to)=0.37% and epsilon(parallel to)=-0.37% for InGaN, respectively, were derived using the XRD measurements. The inhomogeneous strain and the average grain size of the In0.2Ga0.8N/GaN films were also studied by XRD. Photoluminescence spectra were used to measure the optical characterization of the InxGa1-xN thin films with different In composition, and the near-band-edge emission dependence of cubic InxGa1-xN on the x value is nearly linear with In content x less than or equal to 0.24. (C) 2000 American Institute of Physics. [S0021-8979(00)03908-6].

Normal-incidence intersubband (In, Ga)As/GaAs quantum dot infrared photodetectors

We report the device performance of normal-incidence (In, Ga)As/GaAs quantum dot intersubband infrared photodetectors. A primary intersubband transition peak is observed at the wavelength of 13 mu m (E-0 --> E-1) and a secondary peak at 11 mu m (E-0 --> E-2). The measured energy spacing in the conduction band of the quantum dots is in good agreement with low temperature photoluminescence measurement and calculations. A peak detectivity of 1 x 10(10) cm Hz(1/2)/W at 13 mu m was achieved at 40 K for these devices. (C) 1998 American Institute of Physics. [S0003-6951(98)01440-5].

Tunneling magnetoresistance in (Ga,Mn)As/Al-O/CoFeB hybrid structures

Tunneling magnetoresistance (TMR) in Ga(0.9)2Mn(0.08)As/Al-O/Co40Fe40B20 trilayer hybrid structure as a function of temperature from 10 to 50 K with magnetic field vertical bar H vertical bar <= 2000 Oe has been studied. TMR ratio of 1.6% at low fields at 10 K was achieved with the applied current of 1 mu A. The behavior of junction resistance was well explained by the tunneling resistance across the barrier. Strong bias dependences of magnetoresistance and junction resistance were presented. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068418]

Research of Face Detection System Applied for Detecting Faces with Complex Background and Illumination

An effective face detection system used for detecting multi pose frontal face in gray images is presented. Image preprocessing approaches are applied to reduce the influence of the complex illumination. Eye-analog pairing and improved multiple related template matching are used to glancing and accurate face detecting, respectively. To shorten the time cost of detecting process, we employ prejudge rules in checking candidate image segments before template matching. Test by our own face database with complicated illumination and background, the system has high calculation speed and illumination independency, and obtains good experimental results.

Research of Face Location System Based on Human Vision Simulations

In this paper we present a robust face location system based on human vision simulations to automatically locate faces in color static images. Our method is divided into four stages. In the first stage we use a gauss low-pass filter to remove the fine information of images, which is useless in the initial stage of human vision. During the second and the third stages, our technique approximately detects the image regions, which may contain faces. During the fourth stage, the existence of faces in the selected regions is verified. Having combined the advantages of Bottom-Up Feature Based Methods and Appearance-Based Methods, our algorithm performs well in various images, including those with highly complex backgrounds.

Growth Parameter Dependence of Structural Characterizations of Diluted Magnetic Semiconductor (Ga, Cr)As

We report the influence of growth parameters and post-growth annealing on the structural characterizations and magnetic properties of (Ga, Cr)As films. The crystalline quality and magnetic properties are sensitive to the growth conditions. The single-phase (Ga, Cr)As film with the Curie temperature of 10 K is synthesized at growth temperature T-s = 250 degrees C and with nominal Cr content x = 0.016. However, for the films with x > 0.02, the aggregation of Cr atoms is strongly enhanced as both T. and x increase, which not only brings strong compressive strain in the epilayer, but also roughens the surface. The origin of room-temperature ferromagnetism in (Ga, Cr)As films with nanoclusters is also discussed.

A face detection algorithm based on high dimensional space geometry

In this paper, a face detection algorithm which is based on high dimensional space geometry has been proposed. Then after the simulation experiment of Euclidean Distance and the introduced algorithm, it was theoretically analyzed and discussed that the proposed algorithm has apparently advantage over the Euclidean Distance. Furthermore, in our experiments in color images, the proposed algorithm even gives more surprises.

Face recognition based on PCA and multi-degree of freedom neurons

An algorithm of PCA face recognition based on Multi-degree of Freedom Neurons theory is proposed, which based on the sample sets' topological character in the feature space which is different from "classification". Compare with the traditional PCA+NN algorithm, experiments prove its efficiency.

Hypersausage neural networks and its application in face recognition

In this paper, we firstly give the nature of 'hypersausages', study its structure and training of the network, then discuss the nature of it by way of experimenting with ORL face database, and finally, verify its unsurpassable advantages compared with other means.

MVPE Ga 掺杂ZnO 薄膜材料的制备及其在LED 中的应用

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