Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Semiconductor structures”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Characterization of PVT Grown ZnSe by Low Temperature Photoluminescence

ZnSe, a II-VI semiconductor with a large direct band gap of 2.7 eV at room temperature and 2.82 eV at 10 K, is considered a promising material for optoelectric applications in the blue-green region of the spectrum. Photoemitting devices and diode laser action has been demonstrated as a result of decades of research. A key issue in the development of II-VI semiconductors is the control of the concentration of the various impurities. The II-VI semiconductors seem to defy the effort of high level doping due to the well known self compensation of the donors and the acceptors. A good understanding of roles of the impurities and the behavior of the various intrinsic defects such as vacancies, interstitials and their complexes with impurities is necessary in the development and application of these materials. Persistent impurities such as Li and Cu have long played a central role in the photoelectronic properties of many II-VI compounds, particularly ZnSe. The shallow centers which may promote useful electrical conductivity are of particular interest. They contribute the richly structured near gap edge luminescence, containing weak to moderate phonon coupling and therefore very accessible information about the energy states of the different centers. Significance of those residual impurities which may contribute such centers in II-VI semiconductors must be fully appreciated before improved control of their electrical properties may be possible. Low temperature photoluminescence spectroscopy is an important source of information and a useful tool of characterization of II-VI semiconductors such as ZnSe. The low temperature photoluminescence spectrum of a ZnSe single crystal typically consists of a broad band emission peaking at 2.34 eV, known as the Cu-green band, and some very sharp lines near the band gap. These bands and lines are used to identify the impurity ingredients and the defects. The assessment of the quality of the crystal based on the photoluminescence analysis is then possible. In this report we present the characterization of a ZnSe single crystal as grown by the physical vapor transport method, with special intention paid to the possible effects of the gravitational field to the growth of the crystal.

Wang, Ling Jun↗
NASA NTRS1993

Subwavelength structured surfaces and their applications

The term subwavelength structured (SWS) surface describes any surface that contains a subwavelength-period grating or gratings. The grating may be of any type provided the period is sufficiently fine so that, unlike conventional gratings, no diffraction orders propagate other than the zeroth orders. Because of the fine periods involved, the fabrication of such surfaces for applications in the visible and infrared portions of the spectral regime have only recently been considered. With refinements in holographic procedures and the push of the semiconductor industry for submicron lithography, production of SWS surfaces is becoming increasingly viable. The topics covered include the following: analytic approaches to analyze SWS surfaces, 1D periodic stratification and effective medium theory, design of waveplates using form birefringence, and 2D binary antireflection structured surfaces.

Raguin, Daniel H.↗
NASA NTRS2021

Semiconductor to Metal Transition in the Solids/Melts of Te and Pseudo-Binary of Hg1-xCdxTe for x = 0, 0.1 and 0.2

This paper reports the experimentally measured thermal and electrical conductivities from which the Lorenz numbers as functions of temperature were derived for the solids and melts of elemental Te and samples of Hg1-xCdxTe of x = 0, 0.1 and 0.2. The structural changes in the vicinity of the solid-liquid phase transition of elemental Te and various Hg1-xCdxTe solid solutions were assessed by closely examining these experimental properties and the derived Lorenz numbers. The values of Lorenz numbers for the solids of these samples were higher than the value of L0, i.e., the Lorenz number for the free electron gas derived by Sommerfeld, implying the characteristics of non-degenerate semiconductor. With the increasing value of x, or the larger bandgap, the materials become more non-degenerate with larger deviation from L0. As the solids started to melt, the measured values of Lorenz number for all samples started to decrease and eventually reached and maintained at values close to L0 at higher temperatures. The trend of the Lorenz number indicates that the transition from non-degenerate semiconductor of the solid samples to metal or degenerate semiconductor when the samples temperature reached above their liquidus temperatures.

thermal conductivity↗
NASA NTRS2015

Lightweight Integrated Solar Array and Transceiver

The Lightweight Integrated Solar Array and Transceiver (LISA-T) project will leverage several existing and on-going efforts at Marshall Space Flight Center (MSFC) for the design, development, fabrication, and test of a launch stowed, orbit deployed structure on which thin-film photovoltaics for power generation and antenna elements for communication, are embedded. Photovoltaics is a method for converting solar energy into electricity using semiconductor materials. The system will provide higher power generation with a lower mass, smaller stowage volume, and lower cost than the state of the art solar arrays, while simultaneously enabling deployable antenna concepts.

Thin-film photovoltaics↗
NASA NTRSDate not supplied

Comparison of a Probabilistic TID Hardness Assurance Method to Military Standards

The rapid evolution of electronics has heralded countless benefits to humanity, enabling increases in computing power while decreasing costs. However, the constantly changing semiconductor device landscape proves to be an immense challenge for the reliability community, especially for those concerned with radiation effects on microelectronics. Changes in device manufacturing, from device structure to processing steps, may and often do change the way the device responds to radiation. While radiation hardened parts are not as much of a reliability concern, they also lag behind commercial off-the-shelf, or COTS, parts in terms of computing capabilities, some by over a decade. Many missions may have no choice but to utilize COTS. As such, these missions need to ensure their parts are reliable in the face of total ionizing dose (TID). However, part and testing facility costs limit the amount of testing possible.

Chloe Champagne↗
NASA NTRS1995

Silicon Micromachined Sensor for Broadband Vibration Analysis

The development of a family of silicon based integrated vibration sensors capable of sensing mechanical resonances over a broad range of frequencies with minimal signal processing requirements is presented. Two basic general embodiments of the concept were designed and fabricated. The first design was structured around an array of cantilever beams and fabricated using the ARPA sponsored multi-user MEMS processing system (MUMPS) process at the Microelectronics Center of North Carolina (MCNC). As part of the design process for this first sensor, a comprehensive finite elements analysis of the resonant modes and stress distribution was performed using PATRAN. The dependence of strain distribution and resonant frequency response as a function of Young's modulus in the Poly-Si structural material was studied. Analytical models were also studied. In-house experimental characterization using optical interferometry techniques were performed under controlled low pressure conditions. A second design, intended to operate in a non-resonant mode and capable of broadband frequency response, was proposed and developed around the concept of a cantilever beam integrated with a feedback control loop to produce a null mode vibration sensor. A proprietary process was used to integrat a metal-oxide semiconductor (MOS) sensing device, with actuators and a cantilever beam, as part of a compatible process. Both devices, once incorporated as part of multifunction data acquisition and telemetry systems will constitute a useful system for NASA launch vibration monitoring operations. Satellite and other space structures can benefit from the sensor for mechanical condition monitoring functions.

Gutierrez, Adolfo↗
NASA NTRS2004

Dark Current Degradation of Near Infrared Avalanche Photodiodes from Proton Irradiation

InGaAs and Ge avalanche photodiodes (APDs) are examined for the effects of 63-MeV protons on dark current. Dark current increases were large and similar to prior results for silicon APDs, despite the smaller size of InGaAs and Ge devices. Bulk dark current increases from displacement damage in the depletion regions appeared to be the dominant contributor to overall dark current degradation. Differences in displacement damage factors are discussed as they relate to structural and material differences between devices.

indium compounds↗
NASA NTRS2016

Integrated Multi-Color Light Emitting Device Made with Hybrid Crystal Structure

An integrated hybrid crystal Light Emitting Diode ("LED") display device that may emit red, green, and blue colors on a single wafer. The various embodiments may provide double-sided hetero crystal growth with hexagonal wurtzite III-Nitride compound semiconductor on one side of (0001) c-plane sapphire media and cubic zinc-blended III-V or II-VI compound semiconductor on the opposite side of c-plane sapphire media. The c-plane sapphire media may be a bulk single crystalline c-plane sapphire wafer, a thin free standing c-plane sapphire layer, or crack-and-bonded c-plane sapphire layer on any substrate. The bandgap energies and lattice constants of the compound semiconductor alloys may be changed by mixing different amounts of ingredients of the same group into the compound semiconductor. The bandgap energy and lattice constant may be engineered by changing the alloy composition within the cubic group IV, group III-V, and group II-VI semiconductors and within the hexagonal III-Nitrides.

Park, Yeonjoon↗
NASA NTRS2017

Integrated Multi-Color Light Emitting Device Made with Hybrid Crystal Structure

An integrated hybrid crystal Light Emitting Diode ("LED") display device that may emit red, green, and blue colors on a single wafer. The various embodiments may provide double-sided hetero crystal growth with hexagonal wurtzite III-Nitride compound semiconductor on one side of (0001) c-plane sapphire media and cubic zinc-blended III-V or II-VI compound semiconductor on the opposite side of c-plane sapphire media. The c-plane sapphire media may be a bulk single crystalline c-plane sapphire wafer, a thin free standing c-plane sapphire layer, or crack-and-bonded c-plane sapphire layer on any substrate. The bandgap energies and lattice constants of the compound semiconductor alloys may be changed by mixing different amounts of ingredients of the same group into the compound semiconductor. The bandgap energy and lattice constant may be engineered by changing the alloy composition within the cubic group IV, group III-V, and group II-VI semiconductors and within the hexagonal III-Nitrides.

Park, Yeonjoon↗
NASA NTRS1990

New heterojunction LWIR detector options

Researchers investigate the heterojunction internal photoemission (HIP) approach that potentially offers long wavelength infrared (LWIR) photovoltaic detector performance (single pixel) that is competitive with the best of other approaches being considered. Most significantly, this approach offers a relatively simple device technology that promises producible and uniform FPA's. Researchers emphasize an exciting process based on intervalence band absorption. They investigate both III-V and Si-based heterojunctions grown by molecular beam epitaxy (MBE) in which the barrier can be tailored to the desired cutoff wavelength. In addition, MBE allows one to optimize the device structure with precise control of doping profiles and layer thicknesses, and perform band structure engineering by control of composition and heterojunction strain. Researchers also consider free carrier absorption in heterojunctions. Acceptable absorption coefficients can be achieved in very heavily n(exp +) doped semiconductor layers (approx. equals 10(exp 20)cm(exp -3). However, in this case the appreciable filling of conduction band states leads to a Schottky-like photoresponse with a gradual (quadratic) turn-on above threshold. A more satisfactory approach would be to use p(exp +) doping so that with the higher density of states in the heavy hole valence band there would be a narrow band of occupied states. This gives the desirable effect of a more rapid (linear) turn-on above threshold. Unfortunately, the higher hole effective mass also reduces (inversely) the free carrier absorption. For this and other reasons, the intervalence band absorption process looks much more promising.

Maserjian, Joseph↗
NASA NTRS1994

Modes in light wave propagating in semiconductor laser

The study of semiconductor laser based on an analogy of the Schrodinger equation and an equation describing light wave propagation in nonhomogeneous medium is developed. The active region of semiconductor laser is considered as optical waveguide confining the electromagnetic field in the cross-section (x,y) and allowing waveguide propagation along the laser resonator (z). The mode structure is investigated taking into account the transversal and what is the important part of the suggested consideration longitudinal nonhomogeneity of the optical waveguide. It is shown that the Gaussian modes in the case correspond to spatial squeezing and correlation. Spatially squeezed two-mode structure of nonhomogeneous optical waveguide is given explicitly. Distribution of light among the laser discrete modes is presented. Properties of the spatially squeezed two-mode field are described. The analog of Franck-Condon principle for finding the maxima of the distribution function and the analog of Ramsauer effect for control of spatial distribution of laser emission are discussed.

Manko, Margarita A.↗
NASA NTRS1997

Bulk Growth of Wide Band Gap II-VI Compound Semiconductors by Physical Vapor Transport

The mechanism of physical vapor transport of II-VI semiconducting compounds was studied both theoretically, using a one-dimensional diffusion model, as well as experimentally. It was found that the vapor phase stoichiometry is critical in determining the vapor transport rate. The experimental heat treatment methods to control the vapor composition over the starting materials were investigated and the effectiveness of the heat treatments was confirmed by partial pressure measurements using an optical absorption technique. The effect of residual (foreign) gas on the transport rate was also studies theoretically by the diffusion model and confirmed experimentally by the measurements of total pressure and compositions of the residual gas. An in-situ dynamic technique for the transport rate measurements and a further extension of the technique that simultaneously measured the partial pressures and transport rates were performed and, for the first time, the experimentally determined mass fluxes were compared with those calculated, without any adjustable parameters, from the diffusion model. Using the information obtained from the experimental transport rate measurements as guideline high quality bulk crystal of wide band gap II-VI semiconductor were grown from the source materials which undergone the same heat treatment methods. The grown crystals were then extensively characterized with emphasis on the analysis of the crystalline structural defects.

Su, Ching-Hua↗
NASA NTRS1997

Bulk Growth of Wide Band Gap II-VI Compound Semiconductors by Physical Vapor Transport

The mechanism of physical vapor transport of II-VI semiconducting compounds was studied both theoretically, using a one-dimensional diffusion model, as well as experimentally. It was found that the vapor phase stoichiometry is critical in determining the vapor transport rate. The experimental heat treatment methods to control the vapor composition over the starting materials were investigated and the effectiveness of the heat treatments was confirmed by partial pressure measurements using an optical absorption technique. The effect of residual (foreign) gas on the transport rate was also studies theoretically by the diffusion model and confirmed experimentally by the measurements of total pressure and compositions of the residual gas. An in-situ dynamic technique for the transport rate measurements and a further extension of the technique that simultaneously measured the partial pressures and transport rates were performed and, for the first time, the experimentally determined mass fluxes were compared with those calculated, without any adjustable parameters, from the diffusion model. Using the information obtained from the experimental transport rate measurements as guideline high quality bulk crystal of wide band gap II-VI semiconductor were grown from the source materials which undergone the same heat treatment methods. The grown crystals were then extensively characterized with emphasis on the analysis of the crystalline structural defects.

Su, Ching-Hua↗
NASA NTRS1996

Comparison of Non-Parabolic Hydrodynamic Simulations for Semiconductor Devices

Parabolic drift-diffusion simulators are common engineering level design tools for semiconductor devices. Hydrodynamic simulators, based on the parabolic band approximation, are becoming more prevalent as device dimensions shrink and energy transport effects begin to dominate device characteristic. However, band structure effects present in state-of-the-art devices necessitate relaxing the parabolic band approximation. This paper presents simulations of ballistic diodes, a benchmark device, of Si and GaAs using two different non-parabolic hydrodynamic formulations. The first formulation uses the Kane dispersion relationship in the derivation of the conservation equations. The second model uses a power law dispersion relation {(hk)(exp 2)/2m = xW(exp Y)}. Current-voltage relations show that for the ballistic diodes considered. the non-parabolic formulations predict less current than the parabolic case. Explanations of this will be provided by examination of velocity and energy profiles. At low bias, the simulations based on the Kane formulation predict greater current flow than the power law formulation. As the bias is increased this trend changes and the power law predicts greater current than the Kane formulation. It will be shown that the non-parabolicity and energy range of the hydrodynamic model based on the Kane dispersion relation are limited due to the binomial approximation which was utilized in the derivation.

Smith, A. W.↗
NASA NTRS2010

Nanoionics-Based Switches for Radio-Frequency Applications

Nanoionics-based devices have shown promise as alternatives to microelectromechanical systems (MEMS) and semiconductor diode devices for switching radio-frequency (RF) signals in diverse systems. Examples of systems that utilize RF switches include phase shifters for electronically steerable phased-array antennas, multiplexers, cellular telephones and other radio transceivers, and other portable electronic devices. Semiconductor diode switches can operate at low potentials (about 1 to 3 V) and high speeds (switching times of the order of nanoseconds) but are characterized by significant insertion loss, high DC power consumption, low isolation, and generation of third-order harmonics and intermodulation distortion (IMD). MEMS-based switches feature low insertion loss (of the order of 0.2 dB), low DC power consumption (picowatts), high isolation (>30 dB), and low IMD, but contain moving parts, are not highly reliable, and must be operated at high actuation potentials (20 to 60 V) generated and applied by use of complex circuitry. In addition, fabrication of MEMS is complex, involving many processing steps. Nanoionics-based switches offer the superior RF performance and low power consumption of MEMS switches, without need for the high potentials and complex circuitry necessary for operation of MEMS switches. At the same time, nanoionics-based switches offer the high switching speed of semiconductor devices. Also, like semiconductor devices, nanoionics-based switches can be fabricated relatively inexpensively by use of conventional integrated-circuit fabrication techniques. More over, nanoionics-based switches have simple planar structures that can easily be integrated into RF power-distribution circuits.

Nessel, James↗
NASA NTRS2009

Complementary Barrier Infrared Detector

The complementary barrier infrared detector (CBIRD) is designed to eliminate the major dark current sources in the superlattice infrared detector. The concept can also be applied to bulk semiconductor- based infrared detectors. CBIRD uses two different types of specially designed barriers: an electron barrier that blocks electrons but not holes, and a hole barrier that blocks holes but not electrons. The CBIRD structure consists of an n-contact, a hole barrier, an absorber, an electron barrier, and a p-contact. The barriers are placed at the contact-absorber junctions where, in a conventional p-i-n detector structure, there normally are depletion regions that produce generation-recombination (GR) dark currents due to Shockley-Read- Hall (SRH) processes. The wider-bandgap complementary barriers suppress G-R dark current. The barriers also block diffusion dark currents generated in the diffusion wings in the neutral regions. In addition, the wider gap barriers serve to reduce tunneling dark currents. In the case of a superlattice-based absorber, the superlattice itself can be designed to suppress dark currents due to Auger processes. At the same time, the barriers actually help to enhance the collection of photo-generated carriers by deflecting the photo-carriers that are diffusing in the wrong direction (i.e., away from collectors) and redirecting them toward the collecting contacts. The contact layers are made from materials with narrower bandgaps than the barriers. This allows good ohmic contacts to be made, resulting in lower contact resistances. Previously, THALES Research and Technology (France) demonstrated detectors with bulk InAsSb (specifically InAs0.91Sb0.09) absorber lattice-matched to GaSb substrates. The absorber is surrounded by two wider bandgap layers designed to minimize impedance to photocurrent flow. The wide bandgap materials also serve as contacts. The cutoff wavelength of the InAsSb absorber is fixed. CBIRD may be considered as a modified version of the THALES double heterostructure (DH) p-i-n device, but with even wider bandgap barriers inserted at the contact layer/absorber layer interfaces. It is designed to work with either bulk semiconductors or superlattices as the absorber material. The superlattice bandgap can be adjusted to match the desired absorption cutoff wavelength. This infrared detector has the potential of high-sensitivity operation at higher operating temperatures. This would reduce cooling requirements, thereby reducing the power, mass, and volume of the equipment and allowing an increased mission science return.

Ting, David Z.↗
NASA NTRS2002

Development of High Quantum Efficiency UV/Blue Photocathode Epitaxial Semiconductor Heterostructures for Scintillation and Cherenkov Radiation Detection

The primary goal of this research project was to further extend the use of advanced heteroepitaxial-semiconductor crystal growth techniques such as molecular beam epitaxy (MBE) and to demonstrate significant gains in UV/blue photonic detection by designing and fabricating atomically-tailored heteroepitaxial GaAlN/GaInN photocathode device structures. This NASA Explorer technology research program has focused on the development of photocathodes for Cherenkov and scintillation radiation detection. Support from the program allowed us to enhance our MBE system to include a nitrogen plasma source and a magnetic bearing turbomolecular pump for delivery and removal of high purity atomic nitrogen during GaAlN/GaInN film growth. Under this program we have also designed, built and incorporated a cesium activation stage. In addition, a connected UHV chamber with photocathode transfer/positioner components as well as a hybrid phototube stage was designed and built to make in-situ quantum efficiency measurements without ever having to remove the photocathodes from UHV conditions. Thus we have constructed a system with the capability to couple atomically-tailored MBE-grown photocathode heterostructures with real high gain readout devices for single photon detection evaluation.

Leopold, Daniel J.↗