Search Results

A low-cost approach to fabrication of multinary compounds for energy-related applications

Description: Non-vacuum electrodeposition and electroless deposition techniques with a potential to prepare large-area uniform precursor films using low-cost source materials and low-cost capital equipment are very attractive for the growth of compound materials for superconductors and photovoltaic applications. In the first part, a low-cost electrodeposition (ED) method will be discussed for fabrication of high-temperature Tl-oxide-based superconductors. In the second part, electrodeposition and electroless deposition of semiconductor Cu-In-Ga-Se thin films will be discussed.
Date: January 3, 2000
Creator: Bhattacharya, R.N. & Deb, S.K.
Partner: UNT Libraries Government Documents Department

Chromic mechanism in amorphous WO{sub 3} films

Description: The authors propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO{sub 3{minus}y}{center_dot}nH{sub 2}O). This model not only explains a variety of seemingly conflicting experimental results reported in the literature that cannot be explained by existing models, it also has practical implications with respect to improving the coloring efficiency and durability of electrochromic devices. According to this model, a typical as-deposited tungsten oxide film has tungsten mainly in W{sup 6+} and W{sup 4+} states and can be represented as W{sub 1{minus}y}{sup 6+} W{sub y}{sup 4+}O{sub 3{minus}y}{center_dot}nH{sub 2}O. The proposed chromic mechanism is based on the small polaron transition between the charge-induced W{sup 5+} state and the original W{sup 4+} state instead of the W{sup 5+} and W{sup 6+} states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten oxide films is also discussed.
Date: November 1, 1996
Creator: Zhang, J.G.; Benson, D.K.; Tracy, C.E.; Deb, S.K.; Czanderna, A.W. & Bechinger, C.
Partner: UNT Libraries Government Documents Department

MEASUREMENT OF NANOSTRUCTURES WITH MICROMACHINED MICROSCOPES

Description: We have made reproducible scanning probes with high efficiency, and predictable and reproducible character-istics. We obtained good efficiency with dimensions well below the diffraction limit, so that rela-tively small laser powers in the milliwatt range can be used. For single frequency operation, only low power is necessary to obtain very high fields for the excitation of well-defined Raman scattering, and to work in a reflection mode with good scanning speeds; obtained predictable results with very high fields suitable for obtaining Raman scattering and two-photon scattering; made a scanning probe mounted on a micromachined cantilever to obtain high definition reflection mode images that can be scanned rapidly;and observed Raman scattering using bowtie antennas with CW excitation.
Date: April 30, 2005
Creator: KINO, G.S. & MOERNER, W.E.
Partner: UNT Libraries Government Documents Department

Si Memory Chip as a Sensitive Neutron Detector

Description: A novel neutron detector is based on semiconductor technology. A boron-containing film is an integral part of the semiconductor device and is in physical contact with the charge-storage medium (CSM). The CSM is a proprietary cell design known as MirrorBit{trademark}, which is different from conventional memory designs such as SRAM or DRAM. The design doubles the resolution and sensitivity in the array. This enables a highly effective detection of the secondary particles, {sup 7}Li and {sup 4}He, produced due to neutron capture by {sup 10}B in the device. Other approaches using semiconductor materials for neutron detection have employed single-diode detectors that require off-system preamplifiers to filter and condition the signal. There are several advantages to this non-volatile detector, one being that it requires no power for detection and retains the signal until reset. Further, this detector, a semiconductor chip, can be seamlessly integrated into other systems. Finally, the semiconductor manufacturing process on which the detector is based will allow for a high-volume and low-cost alternative to current detectors. MirrorBit{trademark} chips were exposed to neutron flux and the signals recorded. Detailed results from this experiment will be described in this presentation.
Date: March 1, 2008
Creator: Quam, William
Partner: UNT Libraries Government Documents Department

Photoelectrochemistry of Semiconductor Nanowire Arrays

Description: This project supported research on the growth and photoelectrochemical characterization of semiconductor nanowire arrays, and on the development of catalytic materials for visible light water splitting to produce hydrogen and oxygen. Silicon nanowires were grown in the pores of anodic aluminum oxide films by the vapor-liquid-solid technique and were characterized electrochemically. Because adventitious doping from the membrane led to high dark currents, silicon nanowire arrays were then grown on silicon substrates. The dependence of the dark current and photovoltage on preparation techniques, wire diameter, and defect density was studied for both p-silicon and p-indium phosphide nanowire arrays. The open circuit photovoltage of liquid junction cells increased with increasing wire diameter, reaching 350 mV for micron-diameter silicon wires. Liquid junction and radial p-n junction solar cells were fabricated from silicon nano- and microwire arrays and tested. Iridium oxide cluster catalysts stabilized by bidentate malonate and succinate ligands were also made and studied for the water oxidation reaction. Highlights of this project included the first papers on silicon and indium phosphide nanowire solar cells, and a new procedure for making ligand-stabilized water oxidation catalysts that can be covalently linked to molecular photosensitizers or electrode surfaces.
Date: November 10, 2009
Creator: Mallouk, Thomas E & Redwing, Joan M
Partner: UNT Libraries Government Documents Department

Inverted GaInP/(In)GaAs/InGaAs Triple-Junction Solar Cells with Low-Stress Metamorphic Bottom Junctions: Preprint

Description: We demonstrate high efficiency performance in two ultra-thin, Ge-free III-V semiconductor triple-junction solar cell device designs grown in an inverted configuration. Low-stress metamorphic junctions were engineered to achieve excellent photovoltaic performance with less than 3 x 106 cm-2 threading dislocations. The first design with band gaps of 1.83/1.40/1.00 eV, containing a single metamorphic junction, achieved 33.8% and 39.2% efficiencies under the standard one-sun global spectrum and concentrated direct spectrum at 131 suns, respectively. The second design with band gaps of 1.83/1.34/0.89 eV, containing two metamorphic junctions achieved 33.2% and 40.1% efficiencies under the standard one-sun global spectrum and concentrated direct spectrum at 143 suns, respectively.
Date: May 1, 2008
Creator: Geisz, J. F.; Kurtz, S. R.; Wanlass, M. W.; Ward, J. S.; Duda, A.; Friedman, D. J. et al.
Partner: UNT Libraries Government Documents Department

Design of Shallow P-Type Dopants in ZnO: Preprint

Description: This paper describes approaches to lower the acceptor ionization energy in ZnO by codoping acceptors with donor or isovalent atoms and proposes a universal approach to overcome the doping polarity problem for wide-band-gap semiconductors.
Date: May 1, 2008
Creator: Wei, S.-H.; Li, J. & Yan, Y.
Partner: UNT Libraries Government Documents Department

Advanced numerical methods and software approaches for semiconductor device simulation

Description: In this article the authors concisely present several modern strategies that are applicable to drift-dominated carrier transport in higher-order deterministic models such as the drift-diffusion, hydrodynamic, and quantum hydrodynamic systems. The approaches include extensions of upwind and artificial dissipation schemes, generalization of the traditional Scharfetter-Gummel approach, Petrov-Galerkin and streamline-upwind Petrov Galerkin (SUPG), entropy variables, transformations, least-squares mixed methods and other stabilized Galerkin schemes such as Galerkin least squares and discontinuous Galerkin schemes. The treatment is representative rather than an exhaustive review and several schemes are mentioned only briefly with appropriate reference to the literature. Some of the methods have been applied to the semiconductor device problem while others are still in the early stages of development for this class of applications. They have included numerical examples from the recent research tests with some of the methods. A second aspect of the work deals with algorithms that employ unstructured grids in conjunction with adaptive refinement strategies. The full benefits of such approaches have not yet been developed in this application area and they emphasize the need for further work on analysis, data structures and software to support adaptivity. Finally, they briefly consider some aspects of software frameworks. These include dial-an-operator approaches such as that used in the industrial simulator PROPHET, and object-oriented software support such as those in the SANDIA National Laboratory framework SIERRA.
Date: March 23, 2000
Creator: CAREY,GRAHAM F.; PARDHANANI,A.L. & BOVA,STEVEN W.
Partner: UNT Libraries Government Documents Department

Research Leading to High Throughput Manufacturing of Thin-Film CdTe PV Modules: Annual Subcontract Report, September 2004--September 2005

Description: Specific overall objectives of this subcontract are improvement in baseline field performance of manufactured CdTe PV modules while reducing environmental, health and safety risk in the manufacturing environment. Project objectives focus on four broad categories: (1) development of advanced front-contact window layers, (2) improved semiconductor film deposition, (3) development of improved accelerated life test procedures that indicate baseline field performance, and (4) reduction of cadmium-related environmental, health and safety risks. First Solar has significantly increased manufacturing capacity from less than 2 MW/yr to more than 20 MW/yr, while increasing the average module total-area power conversion efficiency from 7% to >9%. First Solar currently manufactures and sells 50-65-W thin-film CdTe PV modules at a rate of about 1.9 MW/month. Sales backlog (booked sales less current inventory divided by production rate) is more than a year. First Solar is currently building new facilities and installing additional equipment to increase production capacity by 50 MW/yr; the additional capacity is expected to come on line in the third quarter of 2006.
Date: April 1, 2006
Creator: Powell, R. C.
Partner: UNT Libraries Government Documents Department

Time-Resolved Photoluminescence and Photovoltaics

Description: The time-resolved photoluminescence (TRPL) technique and its ability to characterize recombination in bulk photovoltaic semiconductor materials are reviewed. Results from a variety of materials and a few recent studies are summarized and compared.
Date: January 1, 2005
Creator: Metzger, W. K.; Ahrenkiel, R. K.; Dippo, P.; Geisz, J.; Wanlass, M. W. & Kurtz, S.
Partner: UNT Libraries Government Documents Department

Optical Probe for Semiconductor: Cooperative Research and Development Final Report, CRADA Number CRD-06-206

Description: This CRADA involves development of a new semiconductor characterization tool, Optical Probe, which can be commercialized by GT Solar. GT Solar will participate in the design and testing of this instrument that will be developed under an IPP project.
Date: February 1, 2011
Creator: Sopori, B.
Partner: UNT Libraries Government Documents Department

Polymer Based Nanocomposites for Solar Energy Conversion

Description: Organic semiconductor-based photovoltaic devices offer the promise of low cost photovoltaic technology that can be manufactured via large-scale, roll-to-roll printing techniques. Existing organic photovoltaic devices are currently limited to solar power conversion efficiencies of 3?5%. This is because of poor overlap between the absorption spectrum of the organic chromophores and the solar spectrum, non-ideal band alignment between the donor and acceptor species, and low charge carrier mobilities. To address these issues, we are investigating the development of dendrimeric organic semiconductors that are readily synthesized with high purity. They also benefit from optoelectronic properties, such as band gap and band positions, which can be easily tuned by substituting different chemical groups into the molecule. Additionally, we are developing nanostructured oxide/conjugated polymer composite photovoltaics. These composites take advantage of the high electron mobilities attainable in oxide semiconductors and can be fabricated using low-temperature solution-based growth techniques. Here, we discuss the synthesis and preliminary device results of these novel materials and composites.
Date: January 1, 2005
Creator: Shaheen, S.; Olson, D.; White, M.; Mitchell, W.; Miedaner, A.; Curtis, C. et al.
Partner: UNT Libraries Government Documents Department

Bistability of Cation Interstitials in II-VI Semiconductors

Description: The stability of cation interstitials in II-VI semiconductors is studied using ab initio methods. We find that interstitials in the neutral charge state are more stable in the tetrahedral interstitial site near the cation, whereas in the (2+) charge state, they are more stable near the anion. The diffusion energy barrier changes when the defect charge state changes. Therefore, if electrons/holes are taken from the defect level by light, changing its charge state, the interstitial atom will be able to diffuse almost spontaneously due to a reduced diffusion barrier.
Date: November 1, 2005
Creator: Wei, S. H. & Dalpian, G. M.
Partner: UNT Libraries Government Documents Department

Electrostatic Effects in III-V Semiconductor Based Metal-optical Nanostructures

Description: The modification of the band edge or emission energy of semiconductor quantum well light emitters due to image charge induced phenomenon is an emerging field of study. This effect observed in quantum well light emitters is critical for all metal-optics based light emitters including plasmonics, or nanometallic electrode based light emitters. This dissertation presents, for the first time, a systematic study of the image charge effect on semiconductor–metal systems. the necessity of introducing the image charge interactions is demonstrated by experiments and mathematical methods for semiconductor-metal image charge interactions are introduced and developed.
Date: May 2012
Creator: Gryczynski, Karol Grzegorz
Partner: UNT Libraries