Search NASA⌕ Search

SEARCH · Search NASA

Results for “SUPERLATTICES”

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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Strain-Layer-Superlattice Light Modulator

Conceptual device combines resonant reflection and photovoltaic action to enable one light beam to impose spatial and temporal modulation on another light beam. Such spatial light modulator, with high speed and multiplicity of parallel signal channels, used in image processing or similar computation requiring high data-throughput rates. Microstructures of GaAs and InAs with multiple quantum wells and compositional superlattices grown by molecular-beam epitaxy. Enhanced electro-optical properties of arrangement of alternating layers enables writing light beam to modulate reading light beam.

Maserjian, Joseph↗
NASA NTRS1989

Tailorable infrared sensing device with strain layer superlattice structure

An infrared photodetector is formed of a heavily doped p-type Ge(x)Si(1-x)/Si superlattice in which x is pre-established during manufacture in the range 0 to 100 percent. A custom tailored photodetector that can differentiate among close wavelengths in the range of 2.7 to 50 microns is fabricated by appropriate selection of the alloy constituency value, x, to establish a specific wavelength at which photodetection cut-off will occur.

Cheng, Li-Jen↗
NASA NTRS1989

The correlation between the temperature dependence of the CRSS and the formation of superlattice-intrinsic stacking faults in the nickel-base superalloy PWA 1480

The PWA 1480 nickel-base superalloy is known to exhibit a unique minimum in the critical resolved shear stress (CRSS) at about 400 C. This paper reports an observation of a deformation mechanism whose temperature dependence correlates exactly with the reduction in the CRSS. It was found that, after monotonic or cyclic deformation of PWA 1480 at 20 C, the deformation substructures typically contain high density of superlattice-intrinsic stacking faults (S-ISFs) within the gamma-prime precipitates. As the temperature of deformation is increased, the density of S-ISFs is reduced, until finally no faults are observed after deformation in the range from 400 to 705 C. The reduction in the fault density corresponds exactly to the reduction in the CRSS, and the temperature at which the fault density is zero corresponds with the minimum in the CRRS. Two possible mechanisms related to the presence of the S-ISFs in the alloy are considered.

Milligan, Walter W.↗
NASA NTRS1990

Long-wavelength infrared detection in a Kastalsky-type superlattice structure

The first successful demonstration of long-wavelength infrared (LWIR) detection with a Kastalsky-type AlGaAs/GaAs superlattice structure is reported. The experimental response band of the detector is centered near 10 microns in very good agreement with the theoretical response band provided that electron-electron interactions are taken into account. The detector operates at significantly lower bias voltage than photoconductive multiple quantum well LWIR detectors. This could lead to important advantages in applications to photovoltaic detector arrays. The response at 83 K is about 50 percent of the response at 24 K.

Byungsung, O.↗
NASA NTRS1991

Hole-Impeded-Doping-Superlattice LWIR Detectors

Hole-Impeded-Doping-Superlattice (HIDS) InAs devices proposed for use as photoconductive or photovoltaic detectors of radiation in long-wavelength infrared (LWIR) range of 8 to 17 micrometers. Array of HIDS devices fabricated on substrates GaAs or Si. Radiation incident on black surface, metal contacts for picture elements serve as reactors, effectively doubling optical path and thereby increasing absorption of photons. Photoconductive detector offers advantages of high gain and high impedance; photovoltaic detector offers lower noise and better interface to multiplexer readouts.

Maserjian, Joseph↗
NASA NTRS1990

IR detectors based on n-i-p-i superlattices

The principles of operation of n-i-p-i photodetectors are discussed. Special consideration is given to issues that are relevant to the performance of IR detectors such as noise, dark current, and surface effects. In addition, a novel IR detector that promises to provide information about the spectral distribution of the infrared radiation emitted from an object and, consequently, about its temperature, independent of the distance between detector and object is discussed. This detector makes use of the possibility to modulate the internal electric fields of an n-i-p-i superlattice with an applied voltage. By this technique the spectral responsivity of the detector may be controlled electrically and some information about the shape of the emission spectrum may be obtained.

Ruden, P. Paul↗
NASA NTRS1991

Photon-assisted resonant tunneling through variably spaced superlattice energy filters

The observation of photon-assisted resonant tunneling in a multiple quantum well structure composed of doped quantum wells separated by variably space superlattice energy filters is reported. Electrons confined in the quantum wells are excited to the second quantized state by intersubband absorption of incident infrared radiation and are subsequently emitted through the filters under appropriate bias conditions. This is manifested by a distinct peak, with an associated negative differential photoconductance, in the photocurrent versus bias voltage characteristic at low temperatures.

Larsson, A.↗
NASA NTRS1992

Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys, and superlattices: Theoretical study of Cu/graphite bonding

The goals of the research were to provide a fundamental science basis for why the bonding of Cu to graphite is weak, to critically evaluate the previous analysis of the wetting studies with particular regard to the values used for the surface energies of Cu and graphite, and to make recommendations for future experiments or other studies which could advance the understanding and solution of this technological problem. First principles electronic structure calculations were used to study the problem. These are based on density functional theory in the local density approximation and the use of the linear muffin-tin orbital band structure method. Calculations were performed for graphite monolayers, single crystal graphite with the hexagonal AB stacking, bulk Cu, Cu(111) surface, and Cu/graphite superlattices. The study is limited to the basal plane of graphite because this is the graphite plane exposed to Cu and graphite surface energies and combined with the measured contact angles to evaluate the experimental adhesion energy.

Lambrecht, Walter R. L.↗
NASA NTRS1992

Reflection high-energy electron diffraction study of growth and interface formation of the Ga(1-x)In(x)Sb/InAs strained-layer superlattices

Reflection high-energy electron diffraction (RHEED) during molecular beam epitaxy is used to study the growth and interface formation of the Ga(1-x)In(x)Sb/InAs (x is not greater than 0.4) strained-layer superlattices (SLSs) on GaSb(100) substrates. A number of surface atomic structures were observed in the growth of the SLS: a (1 x 3) phase from the InAs epilayer surface, a (2 x 3) phase, a (2 x 4) phase, and diffuse (1 x 1)-like phases from the InAs epilayer surface. It is suggested that the long-range order quality of the interface of Ga(1-x)In(x)Sb on InAs may be better than that of the interface of InAs on Ga(1-x)In(x)Sb, but the abruptness of the interfaces would still be compatible. The RHEED intensity variations in the formation of the interfaces are discussed in terms of interface chemical reactions.

Fan, W. C.↗
NASA NTRS1992

GaAs/AlGaAs superlattice miniband detector with 14.5 microns peak response

Extended long wavelength infrared detection with a miniband-type AlGaAs/GaAs superlattice structure is reported. The experimental response band of the detector is peaked near 14.5 microns in good agreement with the theoretical response, provided that electron-elecltron interactions are taken into account. The detector operates at a low bias voltage, which could lead to important advantages in application to IR focal plane arrays.

Bandara, K. M. S. V.↗
NASA NTRS1992

Localization in one-dimensional random superlattices

The localization of electrons in intentionally disordered superlattices is simulated. By studying the density of states and the localization length, significant variation of the degree of localization is found with the type of random stacking sequence is found. It is predicted that more enhancement of luminescence can be achieved with new types or stacking sequences.

Su, W. P.↗
NASA NTRS1993

Strong far-infrared intersubband absorption under normal incidence in heavily n-type doped nonalloy GaSb-AlSb superlattices

We report on long-wavelength intersubband absorption under normal incidence in heavily doped binary-binary GaSb-AlSb superlattices. Due to a small energy difference between the ellipsoidal L valleys in GaSb and the low-density-of-states Gamma minimum, electrons spill over from the first Gamma subband into the higher-energy L subband in GaSb wells, where they are allowed to make an intersubband transition under normally incident radiation. A peak fractional absorption per quantum well of 6.8 x 10 exp 3 (absorption coefficient alpha of about 8500/cm) is observed at about 15 microns wavelength for a sheet concentration of 1.6 x 10 exp 12 sq cm/well.

Samoska, L. A.↗
NASA NTRS1992

Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys and superlattices

This proposal was mainly concerned with the theoretical study of semiconductor compounds, alloys, and superlattices of interest for photovoltaic applications. In the last year (1991) a study was devoted to metal/graphite bonding in relation to use of graphite fiber reinforcement of Cu for high thermal conductivity applications. The main research topics addressed during the full period of the grant are briefly described: studies of the In-Ga-As ternary system; band-offsets at common anion and InAs/GaSb/AlSb heterojunctions; alloy theory (cluster variation method); and Cu/graphite bonding. Most of the work was described more extensively in previous yearly reports and renewal applications and in publications. The last topic is described more fully in a separate report attached. A list of publications resulting directly from this grant or from other grants but related to this work and of conference presentations is given at the end.

Lambrecht, Walter R. L.↗
NASA NTRS1993

Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

An ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer super lattices grown by MBE at low temperature (500 C) is presented, and results are compared with x ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. It is shown that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. It was also noted that we do not observe any strain effect on the E(sub 1) critical point.

Sieg, R. M.↗
NASA NTRS2006

Progress in MBE grown type-II superlattice photodiodes

We report on the status of GaSb/InAs type-II superlattice diodes grown and fabricated at the Jet Propulsion Laboratory designed for infrared absorption in the 8-12(mu)m range. Recent devices have produced detectivities as high as 8x10 to the tenth power Jones with a differential resistance-area product greater than 6 Ohmcm(sup 2) at 80K with a long wavelength cutoff of approximately 12(mu)m. The measured quantum efficiency of these front-side illuminated devices is close to 30% in the 10-11(mu)m range without antireflection coatings.

molecular beam epitaxy (MBE)↗
NASA NTRS2011

n-B-pi-p Superlattice Infrared Detector

A specially designed barrier (B) is inserted at the n-pi junction [where most GR (generation-recombination) processes take place] in the standard n-pi-p structure to substantially reduce generation-recombination dark currents. The resulting n-Bpi- p structure also has reduced tunneling dark currents, thereby solving some of the limitations to which current type II strained layer superlattice infrared detectors are prone. This innovation is compatible with common read-out integrated circuits (ROICs).

Ting, David Z.↗
NASA NTRS2013

The DUV Stability of Superlattice-Doped CMOS Detector Arrays

In this paper, we present experimental results and band structure calculations that illuminate the unique properties of superlattice-doped detectors. Numerical band structure calculations are presented to analyze the dependencies of surface passivation on dopant profiles and interface trap densities (Figure 3). Experiments and calculations show that quantum-engineered surfaces, grown at JPL by low temperature molecular beam epitaxy, achieve a qualitative as well as quantitative uniqueness in their near-immunity to high densities of surface and interface traps.

doped silicon surfaces↗