Morphological defects and uniformity issues of 4H-SiC homoepitaxial layers grown on off-oriented (0001)Si faces

The morphological defects and uniformity of 4H-SiC epilayers grown by hot wall CVD at 1500 degrees C on off-oriented (0001) Si faces are characterized by atomic force microscope, Nomarski optical microscopy, and Micro-Raman spectroscopy. Typical morphological defects including triangular defects, wavy steps, round pits, and groove defects are observed in mirror-like SiC epilayers. The preparation of the substrate surface is necessary for the growth of high-quality 4H-SiC epitaxial layers with low-surface defect density under optimized growth conditions. (c) 2006 Elsevier Ltd. All rights reserved.

Silicon-on-insulator based optical waveguide and integrated switch matrix

zhangdi于2010-03-29批量导入

Homoepitaxial growth and MOS structures of 4H-SiC on off oriented n-type (0001)Si-faces

Homoepitaxial growth of 4H-SiC on off-oriented n-type Si-face (0001) substrates was performed in a home-made hot-wall low pressure chemical vapor deposition (LPCVD) reactor with SiH4 and C2H4 at temperature of 1500 C and pressure of 20 Torr. The surface morphology and intentional in-situ NH3 doping in 4H-SiC epilayers were investigated by using atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS). Thermal oxidization of 4H-SiC homoepitaxial layers was conducted in a dry O-2 and H-2 atmosphere at temperature of 1150 C. The oxide was investigated by employing x-ray photoelectron spectroscopy (XPS). 4H-SiC MOS structures were obtained and their C-V characteristics were presented.

A switch-on mechanism to activate maize ribosome-inactivating protein for targeting HIV-infected cells

Maize ribosome-inactivating protein (RIP) is a plant toxin that inactivates eukaryotic ribosomes by depurinating a specific adenine residue at the a-sarcin/ricin loop of 28S rRNA. Maize RIP is first produced as a proenzyme with a 25-amino acid internal inactivation region on the protein surface. During germination, proteolytic removal of this internal inactivation region generates the active heterodimeric maize RIP with full N-glycosidase activity. This naturally occurring switch-on mechanism provides an opportunity for targeting the cytotoxin to pathogen-infected cells. Here, we report the addition of HIV-1 protease recognition sequences to the internal inactivation region and the activation of the maize RIP variants by HIV-1 protease in vitro and in HIV-infected cells. Among the variants generated, two were cleaved efficiently by HIV-1 protease. The HIV-1 protease-activated variants showed enhanced N-glycosidase activity in vivo as compared to their un-activated counterparts. They also possessed potent inhibitory effect on p24 antigen production in human T cells infected by two HIV-1 strains. This switch-on strategy for activating the enzymatic activity of maize RIP in target cells provides a platform for combating pathogens with a specific protease.

Structural ordering and interface morphology in symmetrically strained (GaIn)As/Ga(PAs) superlattices grown on off-oriented GaAs(100)

In this work we investigate the structural properties of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of x-ray diffraction, reciprocal-space mapping, and x-ray reflectivity. The multilayers were grown by metalorganic vapor-phase epitaxy on (001) GaAs substrates intentionally off-oriented towards one of the nearest [110] directions. High-resolution triple-crystal reciprocal-space maps recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction clearly show a double periodicity of the x-ray peak intensity that can be ascribed to a lateral and a vertical periodicity occurring parallel and perpendicular to the growth surface. Moreover, from the intensity modulation of the satellite peaks, a lateral-strain gradient within the epilayer unit cell is found, varying from a tensile to a compressive strain. Thus, the substrate off-orientation promotes a lateral modulation of the layer thickness (ordered interface roughness) and of the lattice strain, giving rise to laterally ordered macrosteps. In this respect, contour maps of the specular reflected beam in the vicinity of the (000) reciprocal lattice point were recorded in order to inspect the vertical and lateral interface roughness correlation, A semiquantitative analysis of our results shows that the interface morphology and roughness is greatly influenced by the off-orientation angle and the lateral strain distribution. Two mean spatial wavelengths can be determined, one corresponding exactly to the macrostep periodicity and the other indicating a further interface waviness along the macrosteps. The same spatial periodicities were found on the surface by atomic-force-microscopy images confirming the x-ray results and revealing a strong vertical correlation of the interfaces up to the outer surface.

Gain Switch of an AlGaInP Red Light Semiconductor Laser Diode

We solve the single mode coupled rate equations by computer, simulate the behavior of a gain switch of an AlGalnP red light semiconductor laser diode, and find the characteristic of FWHM of pulses changing with the amplitude of modulation signal, the bias current, and the modulated frequency. On this basis, we conduct experiments. The experiment results accord with the simulations well.

An Improvement on 2× 2 Silicon-on-Insulator Mach-Zehnder Thermo-Optical Switch

An improved 2 ×2 silicon-on-insulator Mach-Zehnder thermo-optical switch is designed and fabricated, which is based on strongly guided multimode interference couplers and single- mode phase-shifting arms. The multimode interference couplers and input/output waveguides are deeply etched to improve coupler performances and coupler-waveguide coupling efficiencies. However, shallow etching is used in the phase-shifting arms to guarantee single-mode property. The strongly guided coupler presents an attractive uniformity about 0. 03 dB and a low propagation loss of -0.6 dB. The 2× 2 switch shows an insertion loss as low as -6.8 dB, where the fiber-waveguide coupling loss of -4.3 dB is included, and the response-time is measured as short as 6.8 μs, which are much better than our previous results.

A 12bit 300MHz Current-Steering CMOS D/A Converter

The proposed DAC consists of a unit current-cell matrix for 8MSBs and a binary-weighted array for 4LSBs, trading-off between the precision, speed, and size of the chip. In order to ensure the linearity of the DAC, a double Centro symmetric current matrix is designed by the Q2 random walk strategy. To achieve better dynamic performance, a latch is added in front of the current switch to change the input signal, such as its optimal cross-point and voltage level. For a 12bit resolution,the converter reaches an update rate of 300MHz.

An Improved Driving Circuit for Thermo-Optical Switch to Improve the Reliability of Thermo-Optical Switch Matrix

The influence of the heaters on the reliability of the thermo-optic (TO) switch matrix is analyzed and an improved driving circuit based on the analyzed results is designed and fabricated. The circuit can improve the reliability of the switch matrix device from 78.87% to 97.04% for a 4×4 optical switch device with a simplified tree structure. The simulation and experimental results show the circuit can provide suitable driving current for TO switch matrix.

2 x 2 electrooptical switch in silicon-on-insulator waveguide

A 2 x 2 Mach-Zehnder interferometer electrooptical switch integrated in silicon-on-insulator using multimode interference 3-dB couplers as splitter and combiner has been proposed and fabricated. Free carriers plasma dispersion effect was utilized to realize light modulation in silicon. Switching operation was achieved at an injection current of 358mA and which can be much reduced by optimizing the PIN structure and improving fabrication process. Extinction ratio of 7.7dB and crosstalk of 4.8dB has been observed.

The design of cascaded resistors in a new analog switch two-step ADC architecture

In this paper we introduce a new Half-flash analog switch ADC architecture. And we discuss two methods to design the values of the cascaded resistors which generate the reference voltages. Derailed analysis about the effect of analog switches and comparators on reference voltages, and the methods to set the resistor values and correspond;ng voltage errors are given.

An analysis of the performance of a new high-speed single-way analog switch

This paper introduces a new highspeed single-way analog switch which has both highspeed high-resolution mono-direction analog transmission gate function and high-speed digital logic gate function with normal bipolar technology. The analysis of static and transient switching performances as an analog transmission gate is emphasized in the paper. In order to reduce the plug-in effect on high-speed high-resolution systems, an optimum design scheme is also given. This scheme is to achieve accelerated dynamic response with very low bias power dissipation. The analysis of PSPICE simulation as well as the circuit test results confirms the feasibility of the scheme. Now, the circuit has been applied effectively to the designs of novel highspeed A/D and D/A converters.