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Apparent Charge Transfer at Semiconductor Surfaces

Description: We investigate the apparent charge transfer between adatoms in the GeXPb[l.XjGe(lll) interface both experimentally and theoretically. Scanning tunneling microscopy and surface core level measurements suggest significant charge transfer from the Ge adatoms to the Pb adatoms. However, first-principles calculations unambiguously find that the total electronic displacement is negligibly small, and that the results of published experiments can be explained as a result of bond rearrangement.
Date: May 11, 1999
Creator: Carpinelli, Joseph M.; Stumpf, Roland R. & Weitering, Hanno H.
Partner: UNT Libraries Government Documents Department

Femtosecond chirp-free studies of energy relaxation in semiconductor quantum dots: Search for a phonon bottleneck

Description: Contrary to the predictions of phonon bottleneck theories, we observe very fast subpicosecond energy relaxation in strongly confined semiconductor nanocrystals with electron level spacing as large as 20 LO phonon energies.
Date: August 1, 1997
Creator: Klimov, V. & McBranch, D.
Partner: UNT Libraries Government Documents Department

The integration of advanced photonics and MEMS : LDRD 26519 final report.

Description: In this work we have demonstrated the fabrication of two different classes of devices which demonstrate the integration of simple MEMS structures with photonics structures. In the first class of device a suspended, movable Si waveguide was designed and fabricated. This waveguide was designed to be able to be actuated so that it could be brought into close proximity to a ring resonator or similar structure. In the course of this work we also designed a technique to improve the input coupling to the waveguide. While these structures were successfully fabricated, post fabrication and testing involved a significant amount of manipulation of the devices and due to their relatively flimsy nature our structures could not readily survive this extra handling. As a result we redesigned our devices so that instead of moving the waveguides themselves we moved a much smaller optical element into close proximity to the waveguides. Using this approach it was also possible to fabricate a much larger array of actively switched photonic devices: switches, ring resonators, couplers (which act as switches or splitters) and attenuators. We successfully fabricated all these structures and were able to successfully demonstrate splitters, switches and attenuators. The quality of the SiN waveguides fabricated in this work were found to be qualitatively compatible to those made using semiconductor materials.
Date: December 1, 2003
Creator: Fleming, James Grant & Lin, Shawn-Yu
Partner: UNT Libraries Government Documents Department

Final Technical and Scientific Report

Description: The objective of this project is to study the ultrafast carrier dynamics of in two types of semiconductor quantum dots: self-assembled quantum dots (SAQDs) and patterned quantum dots (PQDs) and to correlate these dynamics with the shape, size and material composition of the dots, thereby obtaining a fundamental scientific understanding of these nanoscale systems.
Date: July 11, 2007
Creator: Krishna, Sanjay & Hufftaker, Diana
Partner: UNT Libraries Government Documents Department

Band anticrossing in highly mismatched group II-VI semiconductor alloys

Description: We have successfully synthesized highly mismatched Cd{sub 1-y}Mn{sub y}O{sub x}Te{sub 1-x} alloys by high dose implantation of O ions into Cd{sub 1-y}Mn{sub y}Te crystals. In crystals with y > 0.02, incorporation of O causes a large decrease in the band gap. The band gap reduction increases with y; the largest value observed is 190 meV in O-implanted Cd{sub 0.38}Mn{sub 0.62}Te. The results are consistent with the band anticrossing model which predicts that a repulsive interaction between localized states of O located above the conduction band edge and the extended states of the conduction band causes the band gap reduction. A best fit of the measured band gap energies of the O ion synthesized Cd{sub 1-y}Mn{sub y}O{sub x}Te{sub 1-x} alloys using the band anticrossing model for y < 0.55 suggests an activation efficiency of only {approx}5% for implanted O in Cd{sub 1-y}Mn{sub y}Te.
Date: October 3, 2001
Creator: Yu, K.M.; Wu, J.; Walukiewicz, W.; Beeman, J.W.; Ager, J.W.; Haller, E.E. et al.
Partner: UNT Libraries Government Documents Department

Inductively Coupled Plasma Etching of III-V Semiconductors in BCl(3)-Based Chemistries: Part II: InP, InGaAs, InGaAsP, InAs and AllnAs

Description: A parametric study of etch rates and surface morphologies of In-containing compound semiconductors (InP, InGaAs, InGaAsP, InAs and AlInAs) obtained by BClj-based Inductively Coupled Plasmas is reported. Etch rates in the range 1,500-3,000 &min. are obtained for all the materials at moderate source powers (500 W), with the rates being a strong function of discharge composition, rf chuck power and pressure. Typical root-mean-square surface roughness of-5 nm were obtained for InP, which is worse than the values obtained for Ga-based materials under the same conditions (-1 run). The near surface of etched samples is typically slightly deficient in the group V element, but the depth of this deficiency is small (a few tens of angstroms).
Date: December 2, 1998
Creator: Abernathy, C.R.; Han, J.; Hobson, W.S.; Hong, J.; Lambers, E.S.; Lee, J.W. et al.
Partner: UNT Libraries Government Documents Department

An integrated spatial signature analysis and automatic defect classification system

Description: An integrated Spatial Signature Analysis (SSA) and automatic defect classification (ADC) system for improved automatic semiconductor wafer manufacturing characterization is presented. Both concepts of SSA and ADC methodologies are reviewed and then the benefits of an integrated system are described, namely, focused ADC and signature-level sampling. Focused ADC involves the use of SSA information on a defect signature to reduce the number of possible classes that an ADC system must consider, thus improving the ADC system performance. Signature-level sampling improved the ADC system throughput and accuracy by intelligently sampling defects within a given spatial signature for subsequent off-line, high-resolution ADC. A complete example of wafermap characterization via an integrated SSA/ADC system is presented where a wafer with 3274 defects is completely characterized by revisiting only 25 defects on an off-line ADC review station. 13 refs., 7 figs.
Date: August 1, 1997
Creator: Gleason, S.S.; Tobin, K.W. & Karnowski, T.P.
Partner: UNT Libraries Government Documents Department

Compliant substrate technology for dissimilar epitaxy

Description: Strained-layer semiconductor films offer tremendous potential with regards to optoelectronic applications for high speed communications, mobile communications, sensing, and novel logic devices. It is an unfortunate reality that many of the possible film/substrate combinations that could be exploited technologically are off limits because of large differences in lattice parameters, chemical compatibilities, or thermal expansion rates. These mechanical, chemical, and thermal incompatibilities manifest themselves primarily in terms of lattice defects such as dislocations and antiphase boundaries, and in some cases through enhanced surface roughness. An additional limitation, from a production point of view, is money. Device manufacturers as a rule want the cheapest substrate possible. Freeing the heteroepitaxial world of the bonds of (near) lattice matching would vastly expand the types of working devices that could be grown. As a result, a great deal of effort has been expended finding schemes to integrate dissimilar film/substrate materials while preserving the perfection of the film layer. One such scheme receiving significant attention lately is the so-called compliant substrate approach.
Date: March 1, 2000
Partner: UNT Libraries Government Documents Department

Real-space and energy representations for the interface roughness scattering in quantum-well structures

Description: The authors show that the real space representation of the interface-roughness as a fluctuating potential in the coordinate space is equivalent to the usual energy-fluctuation representation for intrasublevel scattering in a single quantum well with a generally shaped confinement-potential profile. The coordinate picture is, however, more general and can be used for higher-order effects and multi-sublevel scattering in coupled multi-quantum-well structures.
Date: April 24, 2000
Partner: UNT Libraries Government Documents Department

Growth and Printability of Multilayer Phase Defects on EUV MaskBlanks

Description: The ability to fabricate defect-free mask blanks is a well-recognized challenge in enabling extreme ultraviolet lithography (EUVL) for semiconductor manufacturing. Both the specification and reduction of defects necessitate the understanding of their printability and how they are generated and grow during Mo-Si multilayer (ML) deposition. A ML phase defect can be depicted by its topographical profile on the surface as either a bump or pit, which is then characterized by height or depth and width. The complexity of such seemingly simple phase defects lies in the many ways they can be generated and the difficulties of measuring their physical shape/size and optical effects on printability. An effective way to study phase defects is to use a programmed defect mask (PDM) as 'model' test sample where the defects are produced with controlled growth on a ML blank and accurate placement in varying proximity to absorber patterns on the mask. This paper describes our recent study of ML phase defect printability with resist data from exposures of a ML PDM on the EUV micro-exposure tool (MET, 5X reduction with 0.3NA).
Date: June 10, 2007
Creator: Liang, Ted; Ultanir, Erdem; Zhnag, Guojing; Park, Seh-Jin; Anderson, Erik; Gullikson, Eric et al.
Partner: UNT Libraries Government Documents Department

Highly Mismatched Alloys for Intermediate Band Solar Cells

Description: It has long been recognized that the introduction of a narrow band of states in a semiconductor band gap could be used to achieve improved power conversion efficiency in semiconductor-based solar cells. The intermediate band would serve as a ''stepping stone'' for photons of different energy to excite electrons from the valence to the conduction band. An important advantage of this design is that it requires formation of only a single p-n junction, which is a crucial simplification in comparison to multijunction solar cells. A detailed balance analysis predicts a limiting efficiency of more than 50% for an optimized, single intermediate band solar cell. This is higher than the efficiency of an optimized two junction solar cell. Using ion beam implantation and pulsed laser melting we have synthesized Zn{sub 1-y}Mn{sub y}O{sub x}Te{sub 1-x} alloys with x<0.03. These highly mismatched alloys have a unique electronic structure with a narrow oxygen-derived intermediate band. The width and the location of the band is described by the Band Anticrossing model and can be varied by controlling the oxygen content. This provides a unique opportunity to optimize the absorption of solar photons for best solar cell performance. We have carried out systematic studies of the effects of the intermediate band on the optical and electrical properties of Zn{sub 1-y}Mn{sub y}O{sub x}Te{sub 1-x} alloys. We observe an extension of the photovoltaic response towards lower photon energies, which is a clear indication of optical transitions from the valence to the intermediate band.
Date: March 21, 2005
Creator: Walukiewicz, W.; Yu, K.M.; Wu, J.; Ager III, J.W.; Shan, W.; Scrapulla, M.A. et al.
Partner: UNT Libraries Government Documents Department

Final report on LDRD project : advanced optical trigger systems.

Description: Advanced optically-activated solid-state electrical switch development at Sandia has demonstrated multi-kA/kV switching and the path for scalability to even higher current/power. Realization of this potential requires development of new optical sources/switches based on key Sandia photonic device technologies: vertical-cavity surface-emitting lasers (VCSELs) and photoconductive semiconductor switch (PCSS) devices. The key to increasing the switching capacity of PCSS devices to 5kV/5kA and higher is to distribute the current in multiple parallel line filaments triggered by an array of high-brightness line-shaped illuminators. Commercial mechanically-stacked edge-emitting lasers have been used to trigger multiple filaments, but they are difficult to scale and manufacture with the required uniformity. In VCSEL arrays, adjacent lasers utilize identical semiconductor material and are lithographically patterned to the required dimensions. We have demonstrated multiple-line filament triggering using VCSEL arrays to approximate line generation. These arrays of uncoupled circular-aperture VCSELs have fill factors ranging from 2% to 30%. Using these arrays, we have developed a better understanding of the illumination requirements for stable triggering of multiple-filament PCSS devices. Photoconductive semiconductor switch (PCSS) devices offer advantages of high voltage operation (multi-kV), optical isolation, triggering with laser pulses that cannot occur accidentally in nature, low cost, high speed, small size, and radiation hardness. PCSS devices are candidates for an assortment of potential applications that require multi-kA switching of current. The key to increasing the switching capacity of PCSS devices to 5kV/5kA and higher is to distribute the current in multiple parallel line filaments triggered by an array of high-brightness line-shaped illuminators. Commercial mechanically-stacked edge-emitting lasers have been demonstrated to trigger multiple filaments, but they are difficult to scale and manufacture with the required uniformity. As a promising alternative to multiple discrete edge-emitting lasers, a single wafer of vertical-cavity surface-emitting lasers (VCSELs) can be lithographically patterned to achieve the desired layout of parallel line-shaped ...
Date: September 1, 2008
Creator: Roose, Lars D.; Hadley, G. Ronald; Mar, Alan; Serkland, Darwin Keith; Geib, Kent Martin; Sullivan, Charles Thomas et al.
Partner: UNT Libraries Government Documents Department

Comparison of Wide-Bandgap Semiconductors for Power Electronics Applications

Description: Recent developmental advances have allowed silicon (Si) semiconductor technology to approach the theoretical limits of the Si material; however, power device requirements for many applications are at a point that the present Si-based power devices cannot handle. The requirements include higher blocking voltages, switching frequencies, efficiency, and reliability. To overcome these limitations, new semiconductor materials for power device applications are needed. For high power requirements, wide-bandgap semiconductors like silicon carbide (SiC), gallium nitride (GaN), and diamond, with their superior electrical properties, are likely candidates to replace Si in the near future. This report compares wide-bandgap semiconductors with respect to their promise and applicability for power applications and predicts the future of power device semiconductor materials.
Date: January 2, 2004
Creator: Ozpineci, B.
Partner: UNT Libraries Government Documents Department

High Sensitivity Measurement of Implanted as in the Presence of Ge in Ge(x)Si(1-x)/Si Layered Alloys Using Trace Element Accelerator Mass Spectrometry

Description: This article discusses high sensitivity measurement of implanted As in the presence of Ge in Ge(x)Si(1-x)/Si layered alloys using trace element accelerator mass spectrometry.
Date: December 11, 2000
Creator: Datar, Sameer A.; Wu, Liying; Guo, Baonian N.; Nigam, Mohit; Necsoiu, Daniela; Zhai, Y. J. et al.
Partner: UNT College of Arts and Sciences