Propagation of measurement noise through backprojection reconstruction in electrical impedance tomography

A framework to analyze the propagation of measurement noise through backprojection reconstruction algorithms in electrical impedance tomography (EIT) is presented. Two measurement noise sources were considered: noise in the current drivers and in the voltage detectors. The influence of the acquisition system architecture (serial/semi-parallel) is also discussed. Three variants of backprojection reconstruction are studied: basic (unweighted), weighted and exponential backprojection. The results of error propagation theory have been compared with those obtained from simulated and experimental data. This comparison shows that the approach provides a good estimate of the reconstruction error variance. It is argued that the reconstruction error in EIT images obtained via backprojection can be approximately modeled as a spatially nonstationary Gaussian distribution. This methodology allows us to develop a spatial characterization of the reconstruction error in EIT images.     

The effects of deep-level defects on the electrical properties of Cd0.9Zn0.1Te crystals

The deep-level defects of CdZnTe (CZT) crystals grown by the modified vertical Bridgman (MVB) method act as trapping centers or recombination centers in the band gap, which have significant effects on its electrical properties. The resistivity and electron mobility-lifetime product of high resistivity Cd_0.9Zn_0.1Te wafer marked CZT1 and low resistivity Cd_0.9Zn_0.1Te wafer marked CZT2 were tested respectively. Their deep-level defects were identified by thermally stimulated current (TSC) spectroscopy and thermoelectric effect spectroscopy (TEES) respectively. Then the trap-related parameters were characterized by the simultaneous multiple peak analysis (SIMPA) method. The deep donor level (E_DD)dominating dark current was calculated by the relationship between dark current and temperature. The Fermi-level was characterized by current-voltage measurements of temperature dependence. The width of the band gap was characterized by ultraviolet-visible-infrared transmittance spectroscopy. The results show the traps concentration and capture cross section of CZT1 are lower than CZT2, so its electron mobility-lifetime product is greater than CZT2. The Fermi-level of CZT1 is closer to the middle gap than CZT2. The degree of Fermi-level pinned by EDD of CZT1 is larger than CZT2. It can be concluded that the resistivity of CZT crystals increases as the degree of Fermi-level pinned near the middle gap by the deep donor level enlarges.     

In situ characterization of laser diodes from wide-band electrical noise measurements

The wide-band electrical noise characteristics of 0.8-, 1.3-, and 1.5-μm laser diodes have been studied theoretically and for the first time also experimentally. The electrical noise is related to the optical intensity noise behavior, and can therefore be used for in situ measurements and characterization of laser diodes. Since the measurements are performed without any optical components, undesired optical feedback is eliminated. The results show that several important laser parameters and characteristics can be extracted from purely electrical noise measurements. Among these are the relaxation frequency, the threshold current, the emission linewidth, optical feedback properties, and longitudinal mode hopping behavior. Good agreement between the noise theory and the electrical noise measurements has been obtained. An expression for obtaining both the spectral linewidth and lineshape from electrical noise measurements is also derived.     

Extensive electrical and thermal characterization of an MCM-Dtechnology

In this paper, it is shown the work carried out on thermal characterization of the main materials employed in the deposited-type multichip module (MCM-D) technology. In this technology, silicon chips are mounted onto a silicon substrate by a flipchip technique. The substrates can be either passive with interconnection lines, Rs, Cs, and Ls or active with complementary metal oxide semiconductor (CMOS) technology cells. The metals used in this technology are aluminum for interconnection purposes, tantalum silicide for making resistors and a multilayer of wettable metal for solder connection. Measurements of sheet resistance and contact resistance versus temperature in the range of -28°C to 100°C of the metals used in the technology are shown. A set of classic test structures such as Kelvin contacts, cross bridge resistors (CBR), and Van der Pauw structures have been used for this purpose as well as a new Kelvin-like structure to test the contact resistance of the Flip Chip connection through the ball. This structure has been proven to be very sensitive allowing the measurement of changes in ball resistance in the range of mΩ. A thermal model of the MCM package has been obtained, taking into account all the thermal resistances added by this kind of package     

Structural defects and deep-level centers in 4H-SiC epilayers grown by sublimational epitaxy in vacuum

The parameters of deep-level centers in lightly doped 4H-SiC epilayers grown by sublimational epitaxy and CVD were investigated. Two deep-level centers with activation energies E _c -0.18 eV and E _c -0.65 eV (Z1 center) were observed and tentatively identified with structural defects of the SiC crystal lattice. The Z1 center concentration is shown to fall with decreasing uncompensated donor concentration N _d -N _a in the layers. For the same N _d -N _a , the Z1 center concentration is lower in layers with a higher dislocation density.     

Analog characterization of low-voltage MQW traveling-wave electroabsorption modulators

In this paper, high-speed traveling-wave electroabsorption modulators (TW-EAMs) with strain-compensated InGaAsP multiple quantum wells as the absorption region for analog optical links have been developed. A record-high slope efficiency of 4/V, which is equivalent to a Mach-Zehnder modulator with a V/sub /spl pi// of 0.37 V and a high extinction ratio of > 30 dB/V have been measured. A detailed study of the nonlinearity and the spurious-free dynamic range (SFDR) is presented. By optimizing the bias voltage and the input optical power, the SFDR can be improved by 10-30 dB. After minimizing the third-order distortion, an SFDR as high as 128 dB-Hz/sup 4/5/ is achieved at 10 GHz. A simple link measurement was made using this EAM and an erbium-doped fiber amplifier and a 50-/spl Omega/ terminated photodetector. At 10 GHz, a link gain of 1 dB is achieved at a detected photocurrent of 7.6 mA with higher gains at lower frequencies. The dependence of link gains on bias voltage, input optical, and radio frequency powers are investigated in detail.     

Study of grown-in deep-level defects vs growth parameters in GaAs grown by VPE technique

Studies of the grown-in deep level defects vs substrate orientation and gas phase stoichiometry in the VPE GaAs grown by a novel Ga/AsCl₃/H₂ reactor has been made, using DLTS and C-V methods. Density of electron traps vs Ga/As ratio (i.e., 2/1, 3/1, 4/1, 5/1, and 6/1) was determined for epilayers grown on (100), (211A), and (211B) oriented semi-insulating Cr-doped GaAs substrates. Two electron traps with energies of E_c-0.71 eV (i.e., EB-4) and E_c-0.83 eV (i.e., EL-2) were observed in the samples studied. Results showed that density of both electron traps depends strongly on the Ga/As ratio for the (211A) oriented samples, and less strongly for the (100) oriented samples. In both cases, however, the defect density was found to decrease with increasing Ga/As ratio. This result was consistent with the published data in GaAs grown by the VPE, MOCVD, and LEC techniques. Combined thermal and recombination enhanced annealing study on these VPE GaAs specimens showed a significant reduction in the density of the EB4 level and a little reduction in the density of the EL2 level. This Research suported by the Air Force Office of Scientific Research under grant No. AFOSR-81-0187A. Supported by Wright Patterson AFB, under contract No. FF33615-81-C1406.     

Deep cryogenic noise and electrical characterization of thecomplementary heterojunction field-effect transistor (CHFET)

This paper discusses a characterization at 4 K of the complementary heterojunction field-effect transistor (CHFET), to examine its suitability for deep cryogenic (<10 K) readout electronics applications. The CHFET is a GaAs-based transistor analogous in structure and operation to silicon CMOS. The electrical properties including the gate leakage current, subthreshold transconductance, and input-referred noise voltage were examined. It is shown that both n-channel and p-channel CHFET's are fully functional at 4 K, with no anomalous behavior, such as hysteresis or kinks. Complementary circuit designs are possible, and a simple CHFET-based multiplexed op-amp is presented and characterized at 4 K. The noise and gate leakage current of the CHFET are presently several orders of magnitude too large for readout applications, however. The input-referred noise is on the order of 1 μV/√(Hz) at 100 Hz for a 50×50 μm n-channel CHFET. The gate current is strongly dependent on the doping at the gate edge, and is on the order of 10^-14 A for a 10×10 μm ² n-channel CHFET with light gate-edge region doping     

Correlation of noise characteristics and line shape with linewidthrebroadening of MQW DFB lasers

The line shape and noise characteristics of narrow linewidth MQW DFB lasers were measured in the range near the linewidth rebroadening. Excellent correlation between the linewidth rebroadening and line shape change was observed. The linewidth rebroadening is also related to the intensity and frequency noise characteristics     

Compression of picosecond pulses, generated by an electroabsorptionmodulator, in negative dispersion fibres

Optical pulses generated by an electroabsorption modulator are experimentally compressed in various negative-dispersion fibres. Theoretical and experimental pulsewidth evolutions are shown to be in excellent agreement when the voltage-dependent transmission and chirp functions are taken into account     

Study of deep-level defects and annealing effects in undoped and Sn-doped GaAs solar cells irradiated by one-MeV electrons

DLTS and C-V techniques have been employed to determine the defect energy levels and density, carrier capture cross sections, lifetimes and diffusion lengths in the Sn-doped and the undoped GaAs solar cells irradiated by one-MeV electrons under different electron fluences (10¹⁴ to 10¹⁶ cm^?2), fluxes (2 × 10⁹, 4 × 10¹⁰ e/cm²-s), and annealing conditions (150 ? T ? 230°C). The results show that density of both electron and hole traps will in general increase with incresing electron fluence and flux, and decrease with increasing annealing temperature and annealing time. Some distinct difference in defeat spectrum was observed in the undoped and the Sn-doped GaAs solar cells studied. The low temperature thermal annealing and the recombination enhanced annealing processes are found to be very effective in reducing the density of deep-level defects induced by one-MeV electrons. The results of our findings are discussed in detail in this paper.     

Reduction of modal noise in high-speed short-distance computer datalinks by an electrical signal

Measured and calculated data on the tradeoffs between modal noise reduction and intermodulation penalty are presented. The authors quantify how a high modulation bandwidth and optical power can be obtained using conventional high-speed semiconductor lasers, by combining a sinusoidal auxiliary microwave signal with the normal data signal. How the characteristics of the laser diode determine the optimum values of the auxiliary carrier parameters is shown. Some results of optical data link simulations are presented. A 2.4-Gb/s transmission experiment shows an improvement of the bit error rate due to the microwave signal     

FM noise reduction and subkilohertz linewidth of an AlGaAs laser bynegative electrical feedback

Negative electrical feedback was applied to a CSP-type AlGaAs laser, reducing its FM noise at the Fourier frequency range of f⩽40 MHz. The magnitude of the FM noise was far lower than the quantum noise level of the free-running laser at 100 Hz⩽f ⩽4.4 MHz. It was as low as 1×10^-7~1×10 ^-6 that of the free-running laser at 100 Hz⩽f⩽1 kHz. The full width at half maximum of the field spectrum was reduced to 560 Hz. The major factors necessary for realizing the very low FM noise level were: (1) the laser had almost constant FM response characteristics for a wide Fourier frequency range; (2) a high-finesse Fabry-Perot interferometer was employed for highly-sensitive FM noise detection and to get higher feedback gain; (3) the reflection mode of the Fabry-Perot interferometer was employed to increase the bandwidth and efficiency of the FM noise detection; and (4) a computer simulation was utilized for optimum design of the feedback loop     

Temperature dependence of the width of the deep-level band in silicon with a high concentration of defects

Temperature dependences of the peak location and the half-width of the absorption band related to neutral divacancies in the spectrum of Si irradiated with neutrons at a dose of 10¹⁹ cm^?2 were studied. The results were analyzed in terms of the concept of the defect-level band, whose width depends on the degree of compensation and on temperature.     

Optical characterization of (GaIn)(NAs)/GaAs MQW structures

(GaIn)(NAs)/GaAs multiple quantum well (MQW) structures with high structural perfection as determined from high-resolution x-ray diffraction (XRD) analysis have been deposited by low-temperature metal organic vapor phase epitaxy (MOVPE) at 525°C using triethylgallium (TEGa) and trimethylindium (TMIn) in combination with 1,1-dimethylhydrazine (UDMHy) and tertiarybutylarsine (TBAs). The optical characteristics of as-grown MQW structures as a function of quaternary composition and of well width are established by PL spectroscopy at 300 K. With increasing N-content a reduction in PL efficiency and an increase in PL linewidth is observed. This behavior might be correlated to an increase in defect density with increasing N-content and/or to a bandstructure effect in this novel material system. For an increase in Inconcentration the tendency for a reduction in the extreme bowing of the band gap is detected. Strong quantization effects are observed for well widths below 5 nm only in this novel MQW system, which indicates significantly larger electron masses as compared to N-free (GaIn)As.     

Slow state characterization by measurements of current-voltage characteristics of MOS capacitors

Slow current transients in metal-oxide-semiconductor (MOS) capacitors have been observed and related to slow states located in the oxide within tunneling distance of the silicon. This paper describes slow-state related current transients induced by voltage stepping as the basis of the recently developed technique for both energy-level and time-response characterization of the slow states. The voltage stepping measurements are compared to the standard linear voltage ramping technique.     

高效率聚合物薄膜太阳能电池

本文评述了一种新发明的基于光合作用原理的太阳能电池发电概念。这种太阳能电池具有低的成本和高的理论转换效率。     

A broad-band MQW semiconductor optical amplifier with high saturation output power and low noise figure

A broad-band semiconductor optical amplifier (SOA) that achieves both a high chip saturation output power and a low chip noise figure (NF) was developed by using a thin multiquantum well with low internal loss. The SOA exhibited a high chip saturation output power of >+19.6 dBm and a low chip NF of <4.5 dB over a 3-dB gain bandwidth of 120 nm (1450-1570 nm). For the amplification of optical signals modulated at 40-Gb/s nonreturn-to-zero format, a penalty-free amplification was confirmed up to an average chip output power of +18.1 dBm.