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Quantum efficiency characterization of LBNL CCD's Part 1: theQuantum Efficiency Machine

Description: Instrumentation was developed in 2004 and 2005 to measurethe quantum efficiency of the Lawrence Berkeley National Lab(LBNL)total-depletion CCD's, intended for astronomy and spaceapplications. This paper describes the basic instrument. Although it isconventional even to the parts list, there are important innovations. Axenon arc light source was chosen for its high blue/UV and low red/IRoutput as compared with a tungsten light. Intensity stabilization hasbeen difficult, but sinceonly flux ratios matter this is not critical.Between the light source andan Oriel MS257 monochromator are a shutterand two filter wheels. High-bandpass and low-bandpass filter pairsisolate the 150-nm wide bands appropriate to the wavelength, thusminimizing scattered light and providing order blocking. Light from theauxiliary port enters a 20-inch optical sphere, and the 4-inch outputport is at right angles to the input port. An 80 cm drift space producesnear-uniform illumination on the CCD. Next to the cold CCD inside thehorizontal dewar is a calibrated reference photodiode which is regulatedto the PD calibration temperature, 25$^\circ$ C. The ratio ofthe CCD andin-dewar reference PD signals provides the QE measurement. Additionalcross-calibration to a PD on the integrating spherepermitslower-intensity exposures.
Date: December 25, 2005
Creator: Groom, Donald E.; Bebek, Christopher J.; Fabricius, Maximilian; Karcher, Armin; Kolbe, William F.; Roe, Natalie A. et al.
Partner: UNT Libraries Government Documents Department

Quantum efficiency characterization of back-illuminated CCDs Part2: reflectivity measurements

Description: The usual quantum efficiency (QE) measurement heavily relies on a calibrated photodiode (PD) and the knowledge of the CCDs gain. Either can introduce significant systematic errors. But reflectivity can also be used to verify QE measurements. 1 - R > QE, where R is the reflectivity, and over a significant wavelength range, 1 - R = QE. An unconventional reflectometer has been developed to make this measurement. R is measured in two steps, using light from the lateral monochromator port via an optical fiber. The beam intensity is measured directly with aPD, then both the PD and CCD are moved so that the optical path length is unchanged and the light reflects once from the CCD; the PD current ratio gives R. Unlike traditional schemes this approach makes only one reflection from the CCD surface. Since the reflectivity of the LBNL CCDs might be as low as 2 percent this increases the signal to noise ratio dramatically. The goal is a 1 percent accuracy. We obtain good agreement between 1 - R and the direct QE results.
Date: January 19, 2006
Creator: Fabricius, Maximilian H.; Bebek, Chris J.; Groom, Donald E.; Karcher, Armin & Roe, Natalie A.
Partner: UNT Libraries Government Documents Department

Surface and bulk contribution to Cu(111) quantum efficiency

Description: The quantum efficiency (QE) of Cu(111) is measured for different impinging light angles with photon energies just above the work function. We observe that the vectorial photoelectric effect, an enhancement of the QE due to illumination with light with an electric vector perpendicular to the sample surface, is stronger in the more surface sensitive regime. This can be explained by a contribution to photoemission due to the variation in the electromagnetic potential at the surface. The contributions of bulk and surface electrons can then be determined.
Date: November 4, 2008
Creator: Pedersoli, Emanuele; Greaves, Corin Michael Ricardo; Wan, Weishi; Coleman-Smith, Christopher; Padmore, Howard A.; Pagliara, Stefania et al.
Partner: UNT Libraries Government Documents Department

Experience at Fermilab with high quantum efficiency photo-cathodes for rf electron guns

Description: As part of the A0 Photo-injector collaboration at Fermi-lab [1, 2] and the TeSLA collaboration [3], a high bright-ness, low emittance electron source has been developed. In the process, a system was constructed for coating molybde-num cathodes with a layer of cæsium telluride (Cs2 Te), a photo-emissive material of high quantum efficiency (QE). The use of Cs2 Te was first investigated at CERN [4] and LANL [5]. The development of the systems for the TeSLA Test Facility Linac and the Fermilab Photo-injector was done in Milano [6]. The system at Fermilab incorporates manipulator arms to transfer a cathode from the preparation chamber into a 1.3 GHz photo-electron RF gun while it re-mains in an ultra-high vacuum (UHV) environment, in or-der to avoid the deleterious effects of residual gases on the QE. A first prototype electron gun has been operated with a photo-cathode for several months [1]. This paper describes preliminary results obtained with the first 2 photo-cathodes and the first gun. Some of the desired parameters for the TeSLA Test Fa-cility beam are given in Table 1. The desired characteristics for the photo-cathodes include (i) high QE, (ii) high current density (>500 A/cm{sup 2} ), (iii) long lifetime, and (iv) low field emission. The choice of Cs2 Te is a compromise between long lifetime, rugged metal cathodes with low QE (typi-cally between 10{sup -6} and 10{sup -4} and semiconductor cathodes with high QE (>10%), which generally have a short life-time because of their sensitivity to contamination.
Date: October 1998
Creator: Fry, A.; Hahn, E.; Hartung, W.; Kuchnir, M.; Michelato, P. & Sertore, D.
Partner: UNT Libraries Government Documents Department

Lattice-Matched GaInAsSb/A1GaAsSb/GaSb Materials for Thermophotovoltaic Devices

Description: High-performance GaInAsSb/AlGaAsSb/GaSb thermophotovoltaic (TPV) devices with quantum efficiency and fill factor near theoretical limits and open-circuit voltage within about 15% of the limit can be routinely fabricated. To achieve further improvements in TPV device performance, detailed materials studies of GaInAsSb epitaxial growth, the microstructure, and minority carrier lifetime, along with device structure considerations are reported. This paper discusses the materials and device issues, and their implications on TPV device performance. In addition, improvements in TPV performance with integrated distributed Bragg reflectors and back-surface reflectors are discussed.
Date: September 19, 2002
Creator: Wang, C.A.; Vineis, C.J.; Choi, H.K.; Connors, M.K.; Huang, R.H.; Daielson, L.R. et al.
Partner: UNT Libraries Government Documents Department

Photodetectors for Scintillator Proportionality Measurement

Description: We evaluate photodetectors for use in a Compton Coincidence apparatus designed for measuring scintillator proportionality. There are many requirements placed on the photodetector in these systems, including active area, linearity, and the ability to accurately measure low light levels (which implies high quantum efficiency and high signal-to-noise ratio). Through a combination of measurement and Monte Carlo simulation, we evaluate a number of potential photodetectors, especially photomultiplier tubes and hybrid photodetectors. Of these, we find that the most promising devices available are photomultiplier tubes with high ({approx}50%) quantum efficiency, although hybrid photodetectors with high quantum efficiency would be preferable.
Date: October 18, 2010
Creator: Moses, William W.; Choong, Woon-Seng; Hull, Giulia; Payne, Steve; Cherepy, Nerine & Valentine, J.D.
Partner: UNT Libraries Government Documents Department

Measurement of the hybrid photodiode response - Fiber optic window

Description: The hybrid photodiode (HPD[1]) will be used for the CMS HCAL readout [2]. A fiber-optic front window is used to reduce optical cross-talk between the pixels of the multi-pixel HPD�s. A mismatch of numerical aperture between optical fibers carrying light to the HPD window and the fibers composing the fiber-optic front window of the HPD could lead to light loss. The light loss would appear as a reduced effective quantum efficiency of the device. The goal of this set of measurements was to see if there was in fact a reduction in the effective quantum efficiency of the HPD�s.
Date: January 1, 1999
Creator: Ronzhin, A.; Green, D.; Freeman, J. & Barbaro, P. de
Partner: UNT Libraries Government Documents Department

Multi-kiloampere, electron-beam generation from bare aluminum photo-cathodes driven by an ArF laser

Description: An electron-beam-pumped laser operating at ArF (193 nm) producing up to 5.0 joules in a 150-ns pulse has been used to illuminate micro-machined aluminum cathodes. The cathode was pulsed from 2.25- up to 2.95-MV across a 20-cm-AK gap producing fields up to 145 kV/cm using REX (a 4-MeV, 5-kA, 100-ns pulsed diode). Extracted current versus laser power gives a quantum efficiency increasing with power density from 0.07 to 0.11%. The present work is significant in that the cathode operates in the presence of out-gassing materials with a background vacuum pressure in the mid 10{sup {minus}6} torr region and 100-ns-long electron beams of up to 3 kA have been produced. Both emission limited (current follows laser pulse) and space-charge-limited (current follows pulsed power) regimes have been studied up to {approximately} 50 A/cm{sup 2} by varying the cathode diameter. The beam temperature has been measured to be < 5 eV and directly compared in the same experimental setup to velvet based cathodes that measure {approximately} 100 eV.
Date: October 1, 1997
Creator: Carlson, R.L.; Ridlon, R.N.; Seitz, G.J. & Hughes, T.P.
Partner: UNT Libraries Government Documents Department

High-efficiency cell structures and processes applied to photovoltaic-grade Czochralski silicon

Description: The authors performed a detailed study to examine the limiting performance available using photovoltaic-grade Cz silicon. Photovoltaic-grade silicon refers to silicon produced by the photovoltaic industry, which may differ from the silicon used in the semiconductor device industry in impurity and defect concentrations.The study included optimization of fabrication processes, development of advanced device structures, and detailed model calculations to project future performance improvements. Process and device optimization resulted in demonstration of 75-{micro}s bulk lifetimes and 17.6%-efficient large-area cells using photovoltaic-grade Cz silicon. Detailed calculations based on the material and device evaluation of the present work project efficiencies of 20% for photovoltaic-grade Cz silicon with properly optimized processing and device structures.
Date: December 1, 1996
Creator: Gee, J.M.; King, R.R. & Mitchell, K.W.
Partner: UNT Libraries Government Documents Department

Light-trapped, interconnected, Silicon-Film{trademark} modules. Final technical status report

Description: AstroPower has continued its development of an advanced thin-silicon-based photovoltaic module product. This module combines the performance advantages of thin light-trapped silicon layers with the capability of integration into a low-cost, monolithically interconnected module. This report summarized work carried out over a 3-year, cost-shared contract. Key results accomplished during this phase include an NREL-verified conversion efficiency of 12.5% on a 0.47-cm{sup 2} device. The device structure used an insulating substrate and an active layer less than 100 {micro}m thick. A new metalization scheme was designed using insulating crossovers. This technology was demonstrated on a 36-segment, 321-cm{sup 2}, interconnected module. That module was tested at NREL with an efficiency of 9.79%. Further advances in metalization have led to an advanced single back-contact design that will offer low cost through ease of processing and higher performance through reduced shading.
Date: April 1, 1998
Creator: Hall, R.B.; Rand, J.A.; Ford, D.H. & Ingram, A.E.
Partner: UNT Libraries Government Documents Department

Fundamental understanding and development of low-cost, high-efficiency silicon solar cells

Description: The overall objectives of this program are (1) to develop rapid and low-cost processes for manufacturing that can improve yield, throughput, and performance of silicon photovoltaic devices, (2) to design and fabricate high-efficiency solar cells on promising low-cost materials, and (3) to improve the fundamental understanding of advanced photovoltaic devices. Several rapid and potentially low-cost technologies are described in this report that were developed and applied toward the fabrication of high-efficiency silicon solar cells.
Date: May 1, 2000
Partner: UNT Libraries Government Documents Department


Description: Workshop on Photo-injectors for Energy Recovery Linac was held at National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory (BNL) on January 22 and 23, 2001. Fifty people attended the workshop; they came from three countries, representing universities, industries and national laboratories. This is the first workshop ever held on photo-injectors for CW operation, and for the first time, both DC and RF photo-injectors were discussed at the workshop. Workshop covered almost all major issues of photo-injectors, photocathode, laser system, vacuum, DC, 433 MHz/B-factory cavities based RF gun, 1.3 GHz RF gun and beam instrumentation. High quantum efficiency and long live time photocathode is the issue discussed during the workshop. Four working group leaders have done great jobs summarizing the workshop discussion, and identifying the major issues for future R and D.
Date: January 22, 2001
Creator: WANG,X.J.
Partner: UNT Libraries Government Documents Department

Diffraction Grating Structures in Solar Cells

Description: Sub-wavelength periodic texturing (gratings) of crystalline-silicon (c-Si) surfaces for solar cell applications can be designed for maximizing optical absorption in thin c-Si films. We have investigated c-Si grating structures using rigorous modeling, hemispherical reflectance, and internal quantum efficiency measurements. Model calculations predict almost {approximately}100% energy coupling into obliquely propagating diffraction orders. By fabrication and optical characterization of a wide range of 1D & 2D c-Si grating structures, we have achieved broad-band, low ({approximately} 5%) reflectance without an anti-reflection film. By integrating grating structures into conventional solar cell designs, we have demonstrated short-circuit current density enhancements of 3.4 and 4.1 mA/cm{sup 2} for rectangular and triangular 1D grating structures compared to planar controls. The effective path length enhancements due to these gratings were 2.2 and 1.7, respectively. Optimized 2D gratings are expected to have even better performance.
Date: December 1, 2000
Partner: UNT Libraries Government Documents Department

L-shell emission from high-Z solid targets by intense (10{sup 19}W/cm{sup 2}) irradiation with a 248nm laser

Description: Efficient (1.2% yield) multikilovolt x-ray emission from Ba(L) (2.4--2.8{angstrom}) and Gd(L) (1.7--2.1{angstrom}) is produced by ultraviolet (248nm) laser-excited BaF{sub 2} and Gd solids. The high efficiency is attributed to an inner shell-selective collisional electron ejection.
Date: November 22, 1999
Creator: Nelson, T. R.; Borisov, A. B.; Boyer, K.; Schroeder, W. A.; Santoro, J.; Van Tassle, A. J. et al.
Partner: UNT Libraries Government Documents Department

A diffusion model for picosecond electron bunches from negative electron affinity GaAs photo cathodes

Description: Even though theoretical estimates predict response times for the photo emission process of electrons from a negative electron affinity GaAs photo emitter in excess of hundreds of picoseconds, recent measurements found electron bunch durations of 40 ps or less. This work presents precise measurements of picosecond electron bunches from a negative affinity bulk GaAs photo cathode and develops a model which explains the measured bunch durations as well as the observed bunch shapes. The bunch shape turns out to be independent from the quantum efficiency of the photo emitter.
Date: October 27, 1998
Creator: Hartmann, P.; Bermuth, J.; Harrach, D. v.; Hoffmann, J.; Kobis, S.; Reichert, E. et al.
Partner: UNT Libraries Government Documents Department

Characterization of Si nanostructures using internal quantum efficiency measurements

Description: Hemispherical reflectance and internal quantum efficiency measurements have been employed to evaluate the response of Si nanostructured surfaces formed by using random and periodic reactive ion etching techniques. Random RIE-textured surfaces have demonstrated solar weighted reflectance of {approx} 3% over 300--1,200-nm spectral range even without the benefit of anti-reflection films. Random RIE-texturing has been found to be applicable over large areas ({approximately} 180 cm{sup 2}) of both single and multicrystalline Si surfaces. Due to the surface contamination and plasma-induced damage, RIE-textured surfaces did not initially provide increased short circuit current as expected from the enhanced absorption. Improved processing combined with wet-chemical damage removal etches resulted in significant improvement in the short circuit current with IQEs comparable to the random, wet-chemically textured surfaces. An interesting feature of the RIE-textured surfaces was their superior performance in the near IR spectral range. The response of RIE-textured periodic surfaces can be broadly classified into three distinct regimes. One-dimensional grating structures with triangular profiles are characterized by exceptionally low, polarization-independent reflective behavior. The reflectance response of such surfaces is similar to a graded-index anti-reflection film. The IQE response from these surfaces is severely degraded in the UV-Visible spectral region due to plasma-induced surface damage. One-dimensional grating structures with rectangular profiles exhibit spectrally selective absorptive behavior with somewhat similar IQE response. The third type of grating structure combines broadband anti-reflection behavior with significant IQE enhancement in 800--1,200-nm spectral region. The hemispherical reflectance of these 2D grating structures is comparable to random RIE-textured surfaces. The IQE enhancement in the long wavelength spectral region can be attributed to increased coupling into obliquely propagating transmitted diffracted orders inside the Si substrate. Random RIE texturing techniques are expected to find widespread commercial applicability in low-cost, large-area multicrystalline Si solar cells. Grating-texturing techniques are expected to find applications in thin-film and ...
Date: April 1, 2000
Partner: UNT Libraries Government Documents Department

Inner-shell photoionized x-ray lasers

Description: The inner-shell photoionized x-ray lasing scheme is an attractive method for achieving x-ray lasing at short wavelengths, via population inversion following inner-shell photoionization (ISPI). This scheme promises both a short wavelength and a short pulse source of coherent x rays with high average power. In this dissertation a very complete study of the ISPI x-ray laser scheme is done concerning target structure, filter design and lasant medium. An investigation of the rapid rise time of x-ray emission from targets heated by an ultra-short pulse high-intensity optical laser was conducted for use as the x-ray source for ISPI x-ray lasing. Lasing by this approach in C at a wavelength of 45 {angstrom} requires a short pulse (about 50 fsec) driving optical laser with an energy of 1-5 J and traveling wave optics with an accuracy of {approximately} 15 {micro}m. The optical laser is incident on a high-Z target creating a high-density plasma which emits a broadband spectrum of x rays. This x-ray source is passed through a filter to eliminate the low-energy x rays. The remaining high-energy x rays preferentially photoionize inner-shell electrons resulting in a population inversion. Inner-shell photoionized x-ray lasing relies on the large energy of a K-{alpha} transition in the initially neutral lasant. The photo energy required to pump this scheme is only slightly greater than the photon energy of the lasing transition yielding a lasing scheme with high quantum efficiency. However, the overall efficiency is reduced due to low x-ray conversion efficiency and the large probability of Auger decay yielding an overall efficiency of {approximately} 10{sup {minus}7} resulting in an output energy of {micro}J's. They calculate that a driving laser with a pulse duration of 40 fs, a 10{micro}m x 1 cm line focus, and an energy of 1 J gives an effective gain length product (gl) ...
Date: June 1, 1998
Creator: Moon, S.J.
Partner: UNT Libraries Government Documents Department

Engineering the Electronic Band Structure for Multiband Solar Cells

Description: Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.
Date: July 12, 2010
Creator: Lopez, N.; Reichertz, L. A.; Yu, K. M.; Campman, K. & Walukiewicz, W.
Partner: UNT Libraries Government Documents Department

&quot;High Quantum Efficiency of Band-Edge Emission from ZnO Nanowires&quot;

Description: External quantum efficiency (EQE) of photoluminescence as high as 20 percent from isolated ZnO nanowires were measured at room temperature. The EQE was found to be highly dependent on photoexcitation density, which underscores the importance of uniform optical excitation during the EQE measurement. An integrating sphere coupled to a microscopic imaging system was used in this work, which enabled the EQE measurement on isolated ZnO nanowires. The EQE values obtained here are significantly higher than those reported for ZnO materials in forms of bulk, thin films or powders. Additional insight on the radiative extraction factor of one-dimensional nanostructures was gained by measuring the internal quantum efficiency of individual nanowires. Such quantitative EQE measurements provide a sensitive, noninvasive method to characterize the optical properties of low-dimensional nanostructures and allow tuning of synthesis parameters for optimization of nanoscale materials.
Date: December 1, 2010
Creator: Gargas, Daniel; Gao, Hanwei; Wang, Hungta & Peidong, Yang
Partner: UNT Libraries Government Documents Department

CDC and PIN-CMOS Developments for Large Optical Telescope.

Description: Higher quantum efficiency in near-IR, narrower point spread function and higher readout speed than with conventional sensors have been receiving increased emphasis in the development of CCDs and silicon PIN-CMOS sensors for use in large optical telescopes. Some key aspects in the development of such devices are reviewed.
Date: April 3, 2006
Creator: Radeka, V.
Partner: UNT Libraries Government Documents Department

Large-area PSPMT based gamma-ray imager with edge reclamation

Description: We describe a coded aperture, gamma-ray imager which uses a CsI(Na) scintillator coupled to an Hamamatsu R3292 position-sensitive photomultiplier tube (PSPMT) as the position-sensitive detector. We have modified the normal resistor divider readout of the PSPMT to allow use of nearly the full 10 cm diameter active area of the PSPMT with a single scintillator crystal one centimeter thick. This is a significant performance improvement over that obtained with the standard readout technique where the linearity and position resolution start to degrade at radii as small as 3.5 cm with a crystal 0.75 crn thick. This represents a recovery of over 60% of the PSPMT active area. The performance increase allows the construction of an imager with a field of view 20 resolution elements in diameter with useful quantum efficiency from 60-700 keV. In this paper we describe the readout technique, its implementation in a coded aperture imager and the performance of that imager.
Date: September 21, 2000
Creator: Ziock, K-P & Nakae, L
Partner: UNT Libraries Government Documents Department


Description: The development of a suitable photocathode for use in a high average current photoinjector at temperatures ranging from 273 K down to 2 K is a subject of considerable interest, and active research. The choice of photocathode material is often a trade-off made based on the quantum efficiency of the cathode material, the tolerance to adverse vacuum conditions, and the laser wavelength needed to produce photoelectrons. In this paper an overview of the BNL work to date on CsK{sub 2}Sb photocathodes on a variety of substrates, irradiated at multiple wavelengths, and at temperatures down to 170 K will be discussed. The application of this photocathode material into a SRF photoinjector will also be discussed.
Date: May 16, 2005
Creator: BURRILL, A.; BEN-ZVI, I.; RAO, T.; PATE, D. & SEGALOV, Z.
Partner: UNT Libraries Government Documents Department