31 research outputs found
Near contact phenomena and transient effects in far infrared photoconductors
A combination of experimental and modeling work is summarized in two areas: first, the calculation of excess free carrier and space charge distributions near contacts and their effects on device resistivity, and second, the characterization of a slow transient response (tau approx. 1 sec) in Ge:Be detectors which is due to trapping associated with Be(+) formation. In both cases, analytical models, based on continuity and rate equations, have been developed to enable the application of these findings to a wide variety of photoconductor materials
Terawatt-scale photovoltaics: Transform global energy
Solar energy has the potential to play a central role in the future global energy system because of the scale of the solar resource, its predictability, and its ubiquitous nature. Global installed solar photovoltaic (PV) capacity exceeded 500 GW at the end of 2018, and an estimated additional 500 GW of PV capacity is projected to be installed by 2022–2023, bringing us into the era of TW-scale PV. Given the speed of change in the PV industry, both in terms of continued dramatic cost decreases and manufacturing-scale increases, the growth toward TW-scale PV has caught many observers, including many of us (1), by surprise. Two years ago, we focused on the challenges of achieving 3 to 10 TW of PV by 2030. Here, we envision a future with ∼10 TW of PV by 2030 and 30 to 70 TW by 2050, providing a majority of global energy. PV would be not just a key contributor to electricity generation but also a central contributor to all segments of the global energy system. We discuss ramifications and challenges for complementary technologies (e.g., energy storage, power to gas/liquid fuels/chemicals, grid integration, and multiple sector electrification) and summarize what is needed in research in PV performance, reliability, manufacturing, and recycling
Terawatt-scale photovoltaics: Transform global energy
Solar energy has the potential to play a central role in the future global energy system because of the scale of the solar resource, its predictability, and its ubiquitous nature. Global installed solar photovoltaic (PV) capacity exceeded 500 GW at the end of 2018, and an estimated additional 500 GW of PV capacity is projected to be installed by 2022–2023, bringing us into the era of TW-scale PV. Given the speed of change in the PV industry, both in terms of continued dramatic cost decreases and manufacturing-scale increases, the growth toward TW-scale PV has caught many observers, including many of us (1), by surprise. Two years ago, we focused on the challenges of achieving 3 to 10 TW of PV by 2030. Here, we envision a future with ∼10 TW of PV by 2030 and 30 to 70 TW by 2050, providing a majority of global energy. PV would be not just a key contributor to electricity generation but also a central contributor to all segments of the global energy system. We discuss ramifications and challenges for complementary technologies (e.g., energy storage, power to gas/liquid fuels/chemicals, grid integration, and multiple sector electrification) and summarize what is needed in research in PV performance, reliability, manufacturing, and recycling
Reduction Algorithms for the Multiband Imaging Photometer for Spitzer
We describe the data reduction algorithms for the Multiband Imaging
Photometer for Spitzer (MIPS) instrument. These algorithms were based on
extensive preflight testing and modeling of the Si:As (24 micron) and Ge:Ga (70
and 160 micron) arrays in MIPS and have been refined based on initial flight
data. The behaviors we describe are typical of state-of-the-art infrared focal
planes operated in the low backgrounds of space. The Ge arrays are bulk
photoconductors and therefore show a variety of artifacts that must be removed
to calibrate the data. The Si array, while better behaved than the Ge arrays,
does show a handful of artifacts that also must be removed to calibrate the
data. The data reduction to remove these effects is divided into three parts.
The first part converts the non-destructively read data ramps into slopes while
removing artifacts with time constants of the order of the exposure time. The
second part calibrates the slope measurements while removing artifacts with
time constants longer than the exposure time. The third part uses the
redundancy inherit in the MIPS observing modes to improve the artifact removal
iteratively. For each of these steps, we illustrate the relevant laboratory
experiments or theoretical arguments along with the mathematical approaches
taken to calibrate the data. Finally, we describe how these preflight
algorithms have performed on actual flight data.Comment: 21 pages, 16 figures, PASP accepted (May 2005 issue), version of
paper with full resolution images is available at
http://dirty.as.arizona.edu/~kgordon/papers/PS_files/mips_dra.pd
Optical attenuation coefficient in individual ZnO nanowires
Optics Express, Volume 21, No. 5, pp. 6321-6326 (11 March 2013)Attenuation coefficient measurements for the propagation of
bandedge luminescence are made on individual ZnO nanowires by
combining the localized excitation capability of a scanning electron
microscope (SEM) with near-field scanning optical microscopy (NSOM) to
record the distribution and intensity of wave-guided emission.
Measurements were made for individual nanostructures with triangular
cross-sections ranging in diameter from 680 to 2300 nm. The effective
attenuation coefficient shows an inverse dependence on nanowire diameter
(dà à ¢ 1), indicating scattering losses due to non-ideal waveguiding behavior
Optimizing Performance of Far-Infrared Photoconductors: New Approach for Interpretation and Calibration of Transient Response
The goals of the proposed work were to determine if final steady state current values for Ge:Ga photoconductors could be predicted from the initial fast component of the transient response and to develop algorithms to operationalize this approach. This required transient measurements as a function of photon background and signal sizes, for both single shot and modulated signals. In addition, we proposed to address the nature of the hook response and the effects of non-equilibrium background fluctuations
Minority carrier lifetime variations associated with misfit dislocation networks in heteroepitaxial GaInP
The article of record as published may be found at http://dx.doi.org/10.1088/0268-1242/25/5/055017Variations in minority carrier transport properties associated with networks of misfit
dislocations have been measured using a unique optical technique in p-type GaInP grown on
Ge...This work was supported by the National Science Foundation under grant no DMR-0526330 and by the DNDO Academic Research Initiative under grant no ARI/NSF 083007
Cross-Sectional Transport Imaging in a Multijunction Solar Cell
IEEE Journal of PhotovoltaicsThe article of record as published may be found at http://dx.doi.org/10.1109/jphotov.2016.2623088We combine a highly localized electron-beam point source excitation to generate excess free carriers with the spatial resolution of optical near-field imaging to map recombination in a cross-sectioned multijunction (Ga0.5In0.5P/GaIn0.01As/Ge) solar cell. By mapping the spatial variations in emission of light for fixed generation (as opposed to traditional cathodoluminescence (CL), which maps integrated emission as a function of position of generation), it is possible to directly monitor the motion of carri- ers and photons. We observe carrier diffusion throughout the full width of the middle (GaInAs) cell, as well as luminescent coupling from point source excitation in the top cell GaInP to the middle cell. Supporting CL and near-field photoluminescence (PL) measure- ments demonstrate the excitation-dependent Fermi level splitting effects that influence cross-sectioned spectroscopy results, as well as transport limitations on the spatial resolution of conventional cross-sectional far-field measurements.Funded by Naval Postgraduate SchoolFulbright Senior Scholar AwardNational Renewable Energy LaboratoryNational Science FoundationLaboratory and Directed Research and Development progra