Pump-Suppressed Nondegenerate Four-Wave Mixing in a Highly Nonlinear Photonic Crystal Fiber Sagnac Loop

We propose a configuration for suppressing pumps in a broad- and flat-hand tunable nondegenerate four-wave mixing (FWM) wavelength converter. The signal and pumps are coupled into a highly nonlinear photonic crystal fiber symmetrical Sagnac loop. After the FWM wavelength conversion in the loop, the idler is separated from the pumps without a filter. In our experiment, a flat wavelength conversion bandwidth of 36 rim, conversion efficiency of-11 dB., pump-to-signal suppression ratio of 48 dB, and idler-to-pump suppression ratio of 15 dB are achieved.

Frequency dependence of junction capacitance of GaN p-i-n UV detectors

In this paper frequency dependence of small-signal capacitance of p-i-n UV detectors, which were fabricated on GaN grown on sapphire substrate by metalorganic chemical vapor deposition, has been studied. The Schibli-Milnes model was used to analyze the capacitance-frequency characteristics. According to high frequency C-V measurements, the deep level mean concentration is about 2.98 x 10(20) cm(-3). The deep level is caused by the un-ionised Mg dopant. The calculated Mg activation energy is 260 meV and the hole thermal capture cross section of the deep level is about 2.73 x 10(-22) cm(2). The applicability of the Schibli-Milnes model is also discussed when the concentration of deep levels exceeds that of the heavily doped n-side. It is concluded that the analytic expression of the Schibli-Milnes model can still be used to describe the capacitance-frequency characteristics of GaN p-i-n UV detectors in good agreement with experiment. (c) 2005 Elsevier Ltd. All rights reserved.

Electron beam and laser testing on the novel stripixel detectors

The novel Si stripixel detector, developed at BNL (Brookhaven National Laboratory), has been applied in the development of a prototype Si strip detector system for the PHENIX Upgrade at RHIC. The Si stripixel detector can generate X-Y two-dimensional (2D) position sensitivity with single-sided processing and readout. Test stripixel detectors with pitches of 85 and 560 mu m have been subjected to the electron beam test in a SEM set-up, and to the laser beam test in a lab test fixture with an X-Y-Z table for laser scanning. Test results have shown that the X and Y strips are well isolated from each other, and 2D position sensitivity has been well demonstrated in the novel stripixel detectors. (c) 2005 Elsevier B.V. All rights reserved.

A novel hybrid phase-locked-loop frequency synthesizer using single-electron devices and CMOS transistors

This paper proposes a novel phase-locked loop (PLL) frequency synthesizer using single-electron devices (SEDs) and metal-oxide-semiconductor (MOS) field-effect transistors. The PLL frequency synthesizer mainly consists of a single-electron transistor (SET)/MOS hybrid voltage-controlled oscillator circuit, a single-electron (SE) turnstile/MOS hybrid phase-frequency detector (PFD) circuit and a SE turnstile/MOS hybrid frequency divider. The phase-frequency detection and frequency-division functions are realized by manipulating the single electrons. We propose a SPICE model to describe the behavior of the MOSFET-based SE turnstile. The authors simulate the performance of the PILL block circuits and the whole PLL synthesizer. Simulation results indicated that the circuit can well perform the operation of the PLL frequency synthesizer at room temperature. The PILL synthesizer is very compact. The total number of the transistors is less than 50. The power dissipation of the proposed PLL circuit is less than 3 uW. The authors discuss the effect of fabrication tolerance, the effect of background charge and the SE transfer accuracy on the performance of the PLL circuit. A technique to compensate parameter dispersions of SEDs is proposed.

Development of current-based microscopic defect analysis method using optical filling techniques for the defect study on heavily irradiated high-resistivity Si sensors/detectors

Current-based microscopic defect analysis method such as current deep level transient spectroscopy (I-DLTS) and thermally stimulated current have been developed over the years at Brookhaven National Laboratory (BNL) for the defect characterizations on heavily irradiated (Phi(n) >= 10(13) n/cm(2)) high-resistivity (>= 2 k Omega cm) Si sensors/detectors. The conventional DLTS method using a capacitance transient is not valid on heavily irradiated high-resistivity Si sensors/detectors. A new optical filling method, using lasers with various wavelengths, has been applied, which is more efficient and suitable than the traditional voltage-pulse filling. Optimum defect-filling schemes and conditions have been suggested for heavily irradiated high-resistivity Si sensors/detectors. (c) 2006 Published by Elsevier Ltd.

Liquid-phase-epitaxy-grown InAsxSb1-x/GaAs for room-temperature 8-12 mu m infrared detectors

High-quality InAsxSb1-x (0 < x <= 0.3) films are grown on GaAs substrates by liquid phase epitaxy and electrical and optical properties of the films are investigated, revealing that the films exhibit Hall mobilities higher than 2x10(4) cm(2) V-1 s(-1) and cutoff wavelengths longer than 10 mu m at room temperature (RT). Photoconductors are fabricated from the films, and notable photoresponses beyond 8 mu m are observed at RT. In particular, for an InAs0.3Sb0.7 film, a photoresponse of up to 13 mu m with a maximum responsivity of 0.26 V/W is obtained at RT. Hence, the InAsxSb1-x films demonstrate attractive properties suitable for room-temperature, long-wavelength infrared detectors. (c) 2006 American Institute of Physics.

A novel fast lock-in phase-locked loop frequency synthesizer with direct frequency presetting circuit

This paper proposes a novel, fast lock-in, phase-locked loop (PLL) frequency synthesizer. The synthesizer includes a novel mixed-signal voltage-controlled oscillator (VCO) with a direct frequency presetting circuit. The frequency presetting circuit can greatly speed up the lock-in process by accurately the presetting oscillation frequency of the VCO. We fully integrated the synthesizer in standard 0.35 mu m, 3.3 V complementary metal-oxide-semiconductors (CMOS) process. The entire chip area is only 0.4 mm(2). The measured results demonstrate that the synthesizer can speed up the lock-in process significantly and the lock-in time is less than 10 mu s over the entire oscillation frequency range. The measured phase noise of the synthesizer is -85 dBc/Hz at 10 kHz offset. The synthesizer avoids the tradeoff between the lock-in speed and the phase noise/spurs. The synthesizer monitors the chip temperature and automatically compensates for the variation in frequency with temperature.

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength infrared detectors

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength (3-5 mum) infrared detectors are fabricated. The components display photovoltaic-type photocurrent response as well as the bias-controlled modulation of the peak wavelength of the main response, which is ascribed to the Stark shifts of the intersubband transitions from the local ground states to the extended first excited states in the quantum wells, at the 3-5.3 mum infrared atmospheric transmission window. The blackbody detectivity (D-bb*) of the detectors reaches to about 1.0x10(10) cm Hz(1/2)/W at 77 K under bias of +/-7 V. By expanding the electron wave function in terms of normalized plane wave basis within the framework of the effective-mass envelope-function theory, the linear Stark effects of the intersubband transitions between the ground and first excited states in the asymmetric step well are calculated. The obtained results agree well with the corresponding experimental measurements. (C) 2001 American Institute of Physics.

Design, simulation and testing of large area silicon drift detectors and detector array for X-ray spectroscopy

Large area (25 mm(2)) silicon drift detectors and detector arrays (5x5) have been designed, simulated, and fabricated for X-ray spectroscopy. On the anode side, the hexagonal drift detector was designed with self-biasing spiral cathode rings (p(+)) of fixed resistance between rings and with a grounded guard anode to separate surface current from the anode current. Two designs have been used for the P-side: symmetric self-biasing spiral cathode rings (p(+)) and a uniform backside p(+) implant. Only 3 to 5 electrodes are needed to bias the detector plus an anode for signal collection. With graded electrical potential, a sub-nanoamper anode current, and a very small anode capacitance, an initial FWHM of 1.3 keV, without optimization of all parameters, has been obtained for 5.9 keV Fe-55 X-ray at RT using a uniform backside detector.

Improved neutron radiation hardness for Si detectors: Application of low resistivity starting material and or manipulation of N-eff by selective filling of radiation-induced traps at low temperatures

Radiation-induced electrical changes in both space charge region (SCR) of Si detectors and bulk material (BM) have been studied for samples of diodes and resistors made on Si materials with different initial resistivities. The space charge sign inversion fluence (Phi(inv)) has been found to increase linearly with the initial doping concentration (the reciprocal of the resistivity), which gives improved radiation hardness to Si detectors fabricated from low resistivity material. The resistivity of the BM, on the other hand, has been observed to increase with the neutron fluence and approach a saturation value in the order of hundreds k Omega cm at high fluences, independent of the initial resistivity and material type. However, the fluence (Phi(s)), at which the resistivity saturation starts, increases with the initial doping concentrations and the value of Phi(s) is in the same order of that of Phi(inv) for all resistivity samples. Improved radiation hardness can also be achieved by the manipulation of the space charge concentration (N-eff) in SCR, by selective filling and/or freezing at cryogenic temperatures the charge state of radiation-induced traps, to values that will give a much smaller full depletion voltage. Models have been proposed to explain the experimental data.

Structural and photoelectric studies on double barrier quantum well infrared detectors

GaAs/AlAs/GaAlAs double barrier quantum well (DBQW) structures are employed for making 3-5 um photovoltaic infrared (IR) detectors with a peak detectivity of 5 x 10(11) cm Hz(1/2)/W at 80 K. Double crystal X-ray diffraction is combined with synchrotron radiation X-ray analysis to determine successfully the exact thickness of GaAs, AlAs and GaAlAs sublayers. The interband photovoltaic (PV) spectra of the linear array of the detectors are measured directly by edge excitation method, providing the information about spatial separation processes of photogenerated carriers in the multiquantum wells and the distribution of built-in field in the active region. The spectral response of the IR photocurrent of the devices is also measured and compared with the temperature dependent IR absorption of the DBQW samples in order to get a better understanding of the bias-controlled optical and transport behavior of the detector photoresponse and thus to optimize the detector performance. (C) 1999 Elsevier Science Ltd. All rights reserved.

First charge collection and position-precision data on the medium-resistivity silicon strip detectors before and after neutron irradiation up to 2x10(14) n/cm(2)

Test strip detectors of 125 mu m, 500 mu m, and 1 mm pitches with about 1 cm(2) areas have been made on medium-resistivity silicon wafers (1.3 and 2.7 k Ohm cm). Detectors of 500 mu m pitch have been tested for charge collection and position precision before and after neutron irradiation (up to 2 x 10(14) n/cm(2)) using 820 and 1030 nm laser lights with different beam-spot sizes. It has been found that for a bias of 250 V a strip detector made of 1.3 k Ohm cm (300 mu m thick) can be fully depleted before and after an irradiation of 2 x 10(14) n/cm(2). For a 500 mu m pitch strip detector made of 2.7 k Ohm cm tested with an 1030 nm laser light with 200 mu m spot size, the position reconstruction error is about 14 mu m before irradiation, and 17 mu m after about 1.7 x 10(13) n/cm(2) irradiation. We demonstrated in this work that medium resistivity silicon strip detectors can work just as well as the traditional high-resistivity ones, but with higher radiation tolerance. We also tested charge sharing and position reconstruction using a 1030 nm wavelength (300 mu m absorption length in Si at RT) laser, which provides a simulation of MIP particles in high-physics experiments in terms of charge collection and position reconstruction, (C) 1999 Elsevier Science B.V. All rights reserved.

Low Temperature Deposited Nano-structured Vanadium Oxide Thin Films for Uncooled Infrared Detectors

A novel process of room temperature ion beam sputtering deposition of vanadium oxide films and low temperature post annealing for uncooled infrared detectors was proposed in this work. VOx thin films with relatively low square resistance (70 K Omega / square) and large temperature coefficient of resistance (more than 3%/K) at room temperature were fabricated using this low temperature process which was very compatible with the process of uncooled infrared detectors based on micromachined technology. Furthermore, chemical composition and film surface have been characterized using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) respectively. The results showed that the main composition of the processed thin films was V2O5 and the thin films were in the process of crystallization.

Fast Locking and High Accurate Current Matching Phase-Locked Loop

In this paper, a charge-pump based phase-locked loop (CPLL) that can achieve fast locking and tiny deviation is proposed and analyzed. A lock-aid circuit is added to achieve fast locking of the CPLL. Besides, a novel differential charge pump which has good current matching characteristics and a PFD with delay cell has been used in this PLL. The proposed PILL circuit is designed based on the 0.35um 2P4M CMOS process with 3.3V/5V supply voltage. HSPICE simulation shows that the lock time of the proposed CPLL can be reduced by over 72% in comparison to the conventional PILL and its charge pump sink and source current mismatch is only 0.008%.

A Fast-Locking Phase-Locked Loop Using a Seven-State Phase Frequency Detector

A seven-state phase frequency detector (S.S PFD) is proposed for fast-locking charge pump based phase-locked loops (CPPLLs) in this paper. The locking time of the PLL can be significantly reduced by using the seven-state PFD to inject more current into the loop filter. In this stage, the bandwidth of the PLL is increased or decreased to track the phase difference of the reference signal and the feedback signal. The proposed architecture is realized in a standard 0.35 mu m 2P4M CMOS process with a 3.3V supply voltage. The locking time of the proposed PLL is 1.102 mu s compared with the 2.347 mu s of the PLL based on continuous-time PFD and the 3.298 mu s of the PLL based on the pass-transistor tri-state PFD. There are 53.05% and 66.59% reductions of the locking time. The simulation results and the comparison with other PLLs demonstrate that the proposed seven-state PFD is effective to reduce locking time.