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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

High-performance K-band GaAs power field-effect transistors prepared by molecular beam epitaxy

The maturity of the molecular beam epitaxy (MBE) technique for preparing device quality GaAs material for microwave applications is demonstrated by the excellent performance characteristics of K-band GaAs power field-effect transistors (FETs) fabricated on the MBE wafers. An output power of 710 mW with 4.5-dB gain and 17.7 percent power-added efficiency was achieved at 21 GHz with a 1.26-mm gate width pi-gate device. A similar device with a 0.56-mm gate width produced an output power of 320 mW with 5.0-dB gain and 26.6 percent power-added efficiency at 21 GHz. These are the best results yet reported to date for GaAs power FETs operated in the K-band frequency range.

Saunier, P.↗
NASA NTRS1982

Use of column V alkyls in organometallic vapor phase epitaxy (OMVPE)

The use of the column V-trialkyls trimethylarsenic (TMAs) and trimethylantimony (TMSb) for the organometallic vapor phase epitaxy (OM-VPE) of III-V compound semiconductors is reviewed. A general discussion of the interaction chemistry of common Group III and Group V reactants is presented. The practical application of TMSb and TMAs for OM-VPE is demonstrated using the growth of GaSb, GaAs(1-y)Sb(y), Al(x)Ga(1-x)Sb, and Ga(1-x)In(x)As as examples.

Ludowise, M. J.↗
NASA NTRS1985

High-Mobility Epitaxial Silicon Wafers

New technique produces high-mobility multilayer films suitable for use on silicon process line. New material is multilayer film of alternate layers of silicon and alloy of silicon and germanium. Films grown thus far have electron mobilities 50 percent greater than epitaxial silicon films grown previously.

Stermer, R. L., Jr↗
NASA NTRS1983

Cleaning chemistry of GaAs(100) and InSb(100) substrates for molecular beam epitaxy

Ploog (1980) and Bachrach and Krusor (1981) have pointed out the importance of substrate preparation and surface cleaning for obtaining high quality films with the aid of molecular beam epitaxial growth techniques. In the present investigation, high resolution X-ray photoemission (XPS) is used to determine the oxide removal mechanism for GaAs(100) substrates which have undergone a standardized cleaning procedure. Other objectives of the investigation are related to a comparison of different cleaning procedures in order to minimize carbon contamination, the extension of these cleaning techniques to other III-V compound semiconductors such as InSb, and the evaluation of the sensitivity of the compositional results to electron-induced damage effects.

Vasquez, R. P.↗
NASA NTRS1984

Substrate orientation dependence of enhanced epitaxial regrowth of silicon

This work extends the study of dopant-enhanced epitaxial regrowth rate of amorphized Si from the 100 to the 110 and 111 line orientations of Si. Boron and phosphorus dopants are considered. The annealing temperatures are 500 and 550 C. Phosphorus enhances the growth rates in all three orientations by a constant factor of 8.1 + or - 0.9. Boron produces a higher enhancement factor of 12.2 + or - 1.2, except in the case of 100. Implications of the results on various growth models are considered. The crystalline quality of regrown 111 layers is improved in the doped samples.

Ho, K. T.↗
NASA NTRS1984

Lifetimes in Si CVD-epitaxial and other layers determined by spectral LBIC

In an effort to evaluate the minority carrier lifetimes in CVD-epitaxially grown layers in their dependence on the CVD process variables, the absolute spectral LBIC method was found to be the only available method capable of yielding both lifetime and surface recombination velocity in layers, independent of the resistivity of this layer or that of the substrate, as long as they are separated by a pn-junction. With this method, it was not only possible to determine the minority carrier lifetimes in as-grown epi-layers, but to observe their changes through the device fabrication processes. In addition, it was possible for the first time to determine the lifetimes in the alloy-regrowth p(+) layers of base high/low junction structures.

Wolf, M.↗
NASA NTRS1985

Molecular beam epitaxial growth and transmission electron microscopy studies of thin GaAs/InAs(100) multiple quantum well structures

GaAs/InAs(100) multiple interface structures involving 7.4 percent lattice mismatch have been fabricated via molecular beam epitaxy and examined via transmission electron microscopy. It is found that high-quality, dislocation-free interfaces involving such high lattice mismatch can indeed be experimentally realized for very thin layers provided proper care is given to achieve a balance between the growth kinetics and the thermodynamics leading to the equilibrium ground state of the strained layer. The compressive strain is homogeneously accommodated and a tetragonal distortion is induced in the InAs layer with a perpendicular lattice constant in close agreement with that expected on the basis of the continuum theory and elastic constants of bulk InAs.

Grunthaner, F. J.↗
NASA NTRS1986

Compensation in epitaxial cubic SiC films

Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on SiC substrates are reported. The temperature dependent carrier concentrations indicate that the samples are highly compensated. Donor ionization energies, E sub D, are less than one half the values previously reported. The values for E sub D and the donor concentration N sub D, combined with results for small bulk platelets with nitrogen donors, suggest the relation E sub D (N sub D) = E sub D(O) - alpha N sub N sup 1/3 for cubic SiC. A curve fit gives alpha is approx 2.6x10/5 meV cm and E sub D (O) approx 48 meV, which is the generally accepted value of E sub D(O) for nitrogen donors in cubic SiC.

Segall, B.↗
NASA NTRS1986

High-efficiency broad-area single-quantum-well lasers with narrow single-lobed far-field patterns prepared by molecular beam epitaxy

Broad-area single-quantum-well graded-index waveguide separate-confinement heterostructure lasers were fabricated by molecular beam epitaxy. A high external quantum efficiency of 79 percent and stable, single-lobed far-field patterns with a beam divergence as narrow as 0.8 deg (1.9 times diffraction limit) for a 100 micron-wide laser were obtained under pulsed conditions.

Larsson, A.↗
NASA NTRS1986

Growth and characterization of epitaxial SrF2 on InP(100)

The epitaxial growth of 100-262.5-nm SrF2 films on n-type and p-type (100)InP in a conventional baked UHV system at base pressure about 200 ptorr, temperature 250-350 C, and growth rate from less than 100 to about 200 pm/s. Substrates are chemicomechanically polished, degreased, bombarded with 500-eV Ar ions for 3-4 min at 350 C, and annealed for 23-30 min at 350 C, producing a slightly In-rich (In/P = 1.02) In-island-free surface with a (4 x 1) or (1 x 1) LEED structure. Films grown at 350 C and less than 100 pm/s are found to be smooth and free of cracks in most cases, with a highly faceted (1 x 1) LEED structure. The electrical properties of the SrF2 films are found to be acceptable only when the ohmic contacts are applied prior to the substrate prior to SrF2 growth.

Sinharoy, S.↗
NASA NTRS1986

Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping

A study has been made of the effects of adding small amounts of In (0.2-1.2 pct) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by Briones and Collins (1982) and Skromme et al. (1985).

Bhattacharya, P. K.↗
NASA NTRS1986

Compensation in epitaxial cubic SiC films

Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on (100) Si substrates are presented, and the temperature-dependent carrier concentrations are analyzed. Samples are found to be highly compensated (greater than 90 percent) contrary to the assumption made in previously published work, and the donor ionization energies, E(D), are shown to be less than one-half the values quoted previously. New E(D) and donor concentration values, however, provide evidence for identifying the donors as nitrogen in cubic SiC.

Segall, B.↗
NASA NTRS1986

Low energy dislocation structures in epitaxy

The principle of minimum energy was applied to epitaxial interfaces to show the interrelationship beteen misfit, overgrowth thickness and misfit dislocation spacing. The low energy dislocation configurations were presented for selected interfacial geometries. A review of the interfacial energy calculations was made and a critical assessment of the agreement between theory and experiment was presented. Modes of misfit accommodation were presented with emphasis on the distinction between kinetic effects and equilibrium conditions. Two-dimensional and three-dimensional overgrowths were treated together with interdiffusion-modified interfaces, and several models of interfacial structure were treated including the classical and the current models. The paper is concluded by indicating areas of needed investigation into interfacial structure.

Van Der Merwe, Jan H.↗
NASA NTRS1987

Antiphase boundaries in epitaxially grown beta-SiC

When the surface of beta-SiC, grown epitaxially on (001) silicon by chemical vapor deposition, is chemically etched, boundaries appear which may be observed by optical or scanning electron microscopy. Examination by plan-view and cross-sectional transmission electron microscopy shows boundaries in the film which exhibit line or fringe contrast. Convergent beam electron diffraction has been used to show that these boundaries separate domains that are in an antiphase relationship to each other. A model is presented which discusses the formation of these domains from independent nucleation on a stepped substrate surface.

Pirouz, P.↗
NASA NTRS1987

TEM investigation of beta-SiC grown epitaxially on Si substrate by CVD

A transmission electron microscopy study is being conducted on the microstructure of beta-SiC films grown epitaxially on 001-plane silicon by chemical vapor deposition. Observations have been made in plain view and in cross-section. A high density of stacking faults has been found in the bulk of the epilayer which are bounded by partials of the Shockley type with Burgers vectors 1/6 211-line. Cross-sectional high resolution electron microscopy of the interface has shown it to be semicoherent with misfit dislocations to accommodate the lattice parameter difference between the substrate and the epilayer. In addition to misfit dislocations, a high density of twins and some stacking faults are present in the SiC near the interface. Mechanisms for the nucleation and growth of these defects are discussed.

Chorey, C. M.↗
NASA NTRS1988

Molecular-Beam-Epitaxy Program

Molecular Beam Epitaxy (MBE) computer program developed to aid in design of single- and double-junction cascade cells made of silicon. Cascade cell has efficiency 1 or 2 percent higher than single cell, with twice the open-circuit voltage. Input parameters include doping density, diffusion lengths, thicknesses of regions, solar spectrum, absorption coefficients of silicon (data included for 101 wavelengths), and surface recombination velocities. Results include maximum power, short-circuit current, and open-circuit voltage. Program written in FORTRAN IV.

Sparks, Patricia D.↗
NASA NTRS1987

Characterization of graded interface In(x)Ga(1-x)As/In(0.52)Al(0.48)As (x between 0.53 and 0.70) structures grown by molecular-beam epitaxy

Modulation-doped In(x)Ga(1-x)As/In(0.52)Al(0.48)As/InP structures were grown by molecular-beam epitaxy with x values between 53 and 70 percent. For pseudomorphic cases, graded instead of abrupt interfaces were used. Hall mobility and persistent photoconductivity measurements as a function of temperature were used to characterize samples with different structural parameters. Consistent trends in the variation of mobilities and two-dimensional carrier concentration, n(2D), under light and dark conditions have been observed and discussed in terms of applicable scattering mechanisms. The Hall mobilities are comparable to the best results obtained to date but with significantly higher n(2D) concentration.

Peng, C. K.↗
NASA NTRS1988

Minority-carrier lifetime analysis of silicon epitaxy and bulk crystals with nonuniformly distributed defects

Existing analyses of the pulsed response of an MOS capacitor for minority-carrier lifetime determination result in a lifetime value averaged over most of the depletion region width. In this report, an analysis of MOS C-t data is presented that enables minority-carrier generation lifetime to be plotted as a function of depletion region depth. The technique is shown to be useful for samples with bulk or buried interfacial layer defects that have defect-free surfaces. Data are presented for intrinsically gettered bulk crystals and extrinsically gettered Si(2-pct Ge) epitaxial layers with misfit dislocations. In addition, for samples that do have uniform lifetimes, the measurement time required for determining carrier lifetime has been reduced by more than an order of magnitude.

Radzimski, Zbignew↗