Search NASA⌕ Search

SEARCH · Search NASA

Results for “EPITAXIAL DEPOSITION”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Quality control during IC processing

Manual gives detailed test procedures for controlling silicon-wafer processing in manufacture of integrated circuits. Included among 43 test procedures are: ionic, bacterial, and solids contamination of high-purity water needed for wafer processing; crystallographic reflection, purity, and orientation; substrate dimensions and finish; thickness of deposited epitaxial films; oxide quality; photoresist characteristics; pinholes in insulating layers; metallized adhesion; and quality of ohmic contact.

Source record↗
NASA NTRS1979

The study of 'microsurfaces' using thermal desorption spectroscopy

The use of a newly combined ultrahigh vacuum technique for studying continuous and particulate evaporated thin films using thermal desorption spectroscopy (TDS), transmission electron microscopy (TEM), and transmission electron diffraction (TED) is discussed. It is shown that (1) CO thermal desorption energies of epitaxially deposited (111) Ni and (111) Pd surfaces agree perfectly with previously published data on bulk (111) single crystal, (2) contamination and surface structural differences can be detected using TDS as a surface probe and TEM as a complementary technique, and (3) CO desorption signals from deposited metal coverages of one-thousandth of a monolayer should be detectable. These results indicate that the chemisorption properties of supported 'microsurfaces' of metals can now be investigated with very high sensitivity. The combined use of TDS and TEM-TED experimental methods is a very powerful technique for fundamental studies in basic thin film physics and in catalysis.

Thomas, M. E.↗
NASA NTRS1981

Evaluation and verification of epitaxial process sequence for silicon solar-cell production

Several process sequences are shown to be of potentially low cost and to perform effectively when applied to the high quality silicon crystals for which they were developed. The extent to which such process sequences can also perform effectively when applied to lower cost thin film solar cells formed by epitaxial deposition of Si on potentially inexpensive substrates of upgraded metallurgical grade Si was investigated.

Redfield, D.↗
NASA NTRS1981

Evaluation and verification of epitaxial process sequence for silicon solar cell production

The applicability of solar cell and module processing sequences, to be used on lower cost epitaxial silicon wafers was evaluated. The extent to which the process sequences perform effectively when applied to film solar cells formed by epitaxial deposition of Si on potentially inexpensive substrates of upgraded metallurgical grade Si is examined. It is concluded that these substrates are satisfactory in their cell performance.

Redfield, D.↗
NASA NTRS1991

Grooved surfaces on InP

Formation of a textured or grooved front surface on a solar cell can increase the efficiency in several ways, including enhanced absorption and light trapping. In III-IV materials the (111) plane is chemically different form the (1'1'1') plane, and both etching and epitaxial deposition behave differently on these surfaces. The current state of profile etching in InP is summarized. Data are presented on novel geometries attainable as a function of etchant temperature and composition, substrate orientation and carrier concentration, and the oxide thickness between the substrate and the photoresist. Depending on dopant concentration, the same etchant can produce either anisotropic or isotropic grooves. V-grooved solar cells were manufactured on InP, and the improved optical absorption was demonstrated. Preferred parameters for various applications are listed and discussed.

Bailey, Sheila G.↗
NASA NTRS1994

Making CoSi(2) Layers By Ion Implantation

Monolithic photovoltaic batteries containing vertical cells include buried CoSi(2) contact layers. Vertical-junction photovoltaic cells in series fabricated in monolithic structure. N- and p-doped silicon layers deposited epitaxially. The CoSi(2) layers, formed by ion implantation and annealing, serve as thin, low-resistance ohmic contacts between cells.

Namavar, Fereydoon↗
NASA NTRS1994

Microwave GaAs Integrated Circuits On Quartz Substrates

Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

Siegel, Peter H.↗
NASA NTRS2000

Characteristics of Monolithically Integrated InGaAs Active Pixel Imager Array

Switching and amplifying characteristics of a newly developed monolithic InGaAs Active Pixel Imager Array are presented. The sensor array is fabricated from InGaAs material epitaxially deposited on an InP substrate. It consists of an InGaAs photodiode connected to InP depletion-mode junction field effect transistors (JFETs) for low leakage, low power, and fast control of circuit signal amplifying, buffering, selection, and reset. This monolithically integrated active pixel sensor configuration eliminates the need for hybridization with silicon multiplexer. In addition, the configuration allows the sensor to be front illuminated, making it sensitive to visible as well as near infrared signal radiation. Adapting the existing 1.55 micrometer fiber optical communication technology, this integration will be an ideal system of optoelectronic integration for dual band (Visible/IR) applications near room temperature, for use in atmospheric gas sensing in space, and for target identification on earth. In this paper, two different types of small 4 x 1 test arrays will be described. The effectiveness of switching and amplifying circuits will be discussed in terms of circuit effectiveness (leakage, operating frequency, and temperature) in preparation for the second phase demonstration of integrated, two-dimensional monolithic InGaAs active pixel sensor arrays for applications in transportable shipboard surveillance, night vision, and emission spectroscopy.

Kim, Q.↗
NASA NTRS2005

Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

Qiu, Yueming↗
NASA NTRS2003

Process for Smoothing an Si Substrate after Etching of SiO2

A reactive-ion etching (RIE) process for smoothing a silicon substrate has been devised. The process is especially useful for smoothing those silicon areas that have been exposed by etching a pattern of holes in a layer of silicon dioxide that covers the substrate. Applications in which one could utilize smooth silicon surfaces like those produced by this process include fabrication of optical waveguides, epitaxial deposition of silicon on selected areas of silicon substrates, and preparation of silicon substrates for deposition of adherent metal layers. During etching away of a layer of SiO2 that covers an Si substrate, a polymer becomes deposited on the substrate, and the substrate surface becomes rough (roughness height approximately equal to 50 nm) as a result of over-etching or of deposition of the polymer. While it is possible to smooth a silicon substrate by wet chemical etching, the undesired consequences of wet chemical etching can include compromising the integrity of the SiO2 sidewalls and undercutting of the adjacent areas of the silicon dioxide that are meant to be left intact. The present RIE process results in anisotropic etching that removes the polymer and reduces height of roughness of the silicon substrate to less than 10 nm while leaving the SiO2 sidewalls intact and vertical. Control over substrate versus sidewall etching (in particular, preferential etching of the substrate) is achieved through selection of process parameters, including gas flow, power, and pressure. Such control is not uniformly and repeatably achievable in wet chemical etching. The recipe for the present RIE process is the following: Etch 1 - A mixture of CF4 and O2 gases flowing at rates of 25 to 75 and 75 to 125 standard cubic centimeters per minute (stdcm3/min), respectively; power between 44 and 55 W; and pressure between 45 and 55 mtorr (between 6.0 and 7.3 Pa). The etch rate lies between approximately equal to 3 and approximately equal to 6 nm/minute. Etch 2 - O2 gas flowing at 75 to 125 stdcm3/min, power between 44 and 55 W, and pressure between 50 and 100 mtorr (between 6.7 and 13.3 Pa).

Turner, Tasha↗
NASA NTRS1993

A technique for eliminating white phosphorus deposits in vapor phase epitaxy systems

A technique of heating the exhaust lines is described whereby phosphorus in the exhaust portion of an organometallic vapor phase epitaxy reactor is encouraged to deposit in the red form rather than the pyrophoric white form. This technique is simple, effective, and does not hinder or limit the conditions under which the reactor may be operated.

Wilt, D. M.↗
NASA NTRS1993

Organometallic chemical vapor deposition and characterization of ZnGeP2/GaP multiple heterostructures on GaP substrates

The growth of ZnGeP2/GaP double and multiple heterostructures on GaP substrates by organometallic chemical vapor deposition is reported. These epitaxial films were deposited at a temperature of 580 C using dimethylzinc, trimethylgallium, germane, and phosphine as source gases. With appropriate deposition conditions, mirror smooth epitaxial GaP/ZnGeP2 multiple heterostructures were obtained on (001) GaP substrates. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) studies of the films showed that the interfaces are sharp and smooth. Etching study of the films showed dislocation density on the order of 5x10(exp 4)cm(sup -2). The growth rates of the GaP layers depend linearly on the flow rates of trimethylgallium. While the GaP layers crystallize in zinc-blende structure, the ZnGeP2 layers crystallize in the chalcopyrite structure as determined by (010) electron diffraction pattern. This is the first time that multiple heterostructures combining these two crystal structures were made.

Xing, G. C.↗
DOE OSTI2026

Synthesis and composition control of epitaxial FeWO4 thin films using pulsed laser deposition

We report the growth of epitaxial FeWO4 thin films on c-plane sapphire via pulsed laser deposition using a Fe 2 O 3 /WO 3 target ablated in an O 2 atmosphere. At a constant O 2 pressure of 1 mTorr, x-ray diffraction (XRD) confirms FeWO 4 as the major crystalline phase for substrate temperatures from 500 to 800 °C. As temperature increases, x-ray fluorescence (XRF) shows the Fe/W ratio remains nearly constant at 0.90 ± 0.02, while x-ray photoelectron spectroscopy (XPS) shows Fe 3+ to Fe 2+ conversion increases from 20% to 35%. Morphological analysis reveals phase separation, likely of amorphous Fe 3+ oxide from crystalline FeWO 4 , increasing with Fe 3+ conversion. This is attributed to an O-rich laser ablated flux, where conversion is driven by the Arrhenius temperature dependence of Fe 3+ → Fe 2+ reduction on the film surface. At a constant substrate temperature of 750 °C, XRD confirms FeWO 4 formation for O 2 pressures from 0.5 to 10 mTorr. As pressure increases, XRF shows the Fe/W ratio decreases from 0.98 to 0.70, while XPS shows Fe 3+ conversion rises from 15% to 70%. Morphology shows phase separation decreasing with increasing Fe 3+ conversion. This is attributed to scattering, where higher O 2 pressure makes the laser ablated flux O-deficient relative to Fe and W, facilitating Fe 2+ formation. Films with Fe 3+ conversion above ∼30% and Fe/W ratios from 0.86 to 0.96 exhibit FeWO 4 optical and electronic properties suitable for photoanode applications.

36 MATERIALS SCIENCE↗
NASA NTRS1990

AIAs Diffusion/Schottky Barrier on GaAs

Ultrathin epitaxial film of AIAs deposited on GaAs substrate to serve as Schottky barrier and/or as barrier to diffusion. Deposited without interrupting processing vacuum in which substrate deposited and in which any subsequent layers deposited. In new technique, epitaxial film of AIAs deposited directly on GaAs substrate to depth of only two atomic layers - less than 1 nanometer thick. Film thin enough so it does not constitute electronic barrier, but thick enough to act as barrier to interdiffusion of gold and GaAs. Film also used as barrier to interdiffusion of dopants at heterojunctions.

Kaiser, William J.↗
NASA NTRS1966

Fabrication of multilayer dielectric films.

Evaporation system for fabrication of multilayer dielectric films for mirrors or filters, obtaining thickness variation reduction and simultaneous deposition

FILM THICKNESS↗