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Moriarty, J. A.

Publications and source records attributed to Moriarty, J. A..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Silicon superlattices. 2: Si-Ge heterostructures and MOS systems

Five main areas were examined: (1) the valence-and conduction-band-edge electronic structure of the thin layer ( 11 A) silicon-superlattice systems; (2) extension of thin-layer calculations to layers of thickness 11 A, where most potential experimental interest lies; (3) the electronic structure of thicker-layer (11 to 110 A) silicon superlattices; (4) preliminary calculations of impurity-scattering-limited electron mobility in the thicker-layer superlattices; and (5) production of the fine metal lines that would be required to produce on MOS superlattice.

Moriarty, J. A.↗
NASA NTRS1983

Theory of silicon superlattices - Electronic structure and enhanced mobility

A realistic tight-binding band-structure model of silicon superlattices is formulated and used to study systems of potential applied interest, including periodic layered Si-Si(1-x)Ge(x) heterostructures. The results suggest a possible new mechanism for achieving enhanced transverse carrier mobility in such structures: reduced transverse conductivity effective masses associated with the superlattice band structure. For electrons in 100-line-oriented superlattices, a reduced conductivity mass arises intrinsically from the lower symmetry of the superlattice and its unique effect on the indirect bulk silicon band gap. An order of magnitude estimate of the range of mobility enhancement expected from this mechanism appears to be consistent with preliminary experimental results on Si-Si(1-x)Ge(x) superlattices.

Moriarty, J. A.↗
NASA NTRS1981

Silicon superlattices: Theory and application to semiconductor devices

Silicon superlattices and their applicability to improved semiconductor devices were studied. The device application potential of the atomic like dimension of III-V semiconductor superlattices fabricated in the form of ultrathin periodically layered heterostructures was examined. Whether this leads to quantum size effects and creates the possibility to alter familiar transport and optical properties over broad physical ranges was studied. Applications to improved semiconductor lasers and electrondevices were achieved. Possible application of silicon sperlattices to faster high speed computing devices was examined. It was found that the silicon lattices show features of smaller fundamental energyband gaps and reduced effective masses. The effects correlate strongly with both the chemical and geometrical nature of the superlattice.

Moriarty, J. A.↗
NASA NTRS1980

Improved characterization of the Si-SiO2 interface

Refined quasi-static and conductance methods, based on effectively thin composite insulating layers, low-carrier-concentration bulk semiconductors, and low-level illumination, have been applied to an improved characterization of the (100) Si-SiO2 interface. Accurate measurement of both the total density of interface states and its major components as a function of energy in the forbidden gap have been made over four decades (10-billion to 100-trillion states/eV sq cm) on a single sample. The normal U-shaped density of states is resolved into separate valence- and conduction-band-derived contributions as well as impurity-derived contributions corresponding to concentrations on the order of 20 ppm at the interface.

Su, P.↗
NASA NTRS1980

Si and GaAs photocapacitive MIS infrared detectors

Improvement of the previously reported photocapacitive MIS infrared detectors has led to the development of exceptional room-temperature devices. Unoptimized peak detectivities on the order of 10 to the 13th cm sq rt Hz/W, a value which exceeds the best obtainable from existing solid-state detectors, have now been consistently obtained in Si and GaAs devices using high-capacitance LaF3 or composite LaF3/native-oxide insulating layers. The measured spectral response of representative samples is presented and discussed in detail together with a simple theory which accounts for the observed behavior. The response of an ideal MIS photocapacitor is also contrasted with that of both a conventional photoconductor and a p-i-n photodiode, and reasons for the superior performance of the MIS detectors are given. Finally, fundamental studies on the electrical, optical, and noise characteristics of the MIS structures are analyzed and discussed in the context of infrared-detector applications.

Sher, A.↗
NASA NTRS1979

LaF3 insulators for MIS structures

Thin films of LaF3 deposited on Si or GaAs substrates have been observed to form blocking contacts with very high capacitances. This results in comparatively hysteresis-free and sharp C-V (capacitance-voltage) characteristics for MIS structures. Such structures have been used to study the interface states of GaAs with increased resolution and to construct improved photocapacitive infrared detectors.

Sher, A.↗
NASA NTRS1978

Modified lattice-statics approach to dislocation calculations. II - Application

The atomic structure of a screw dislocation core of the 110 line type in aluminum is calculated by the modified lattice-statics method developed in the preceding paper. The method includes anharmonic as well as harmonic forces and permits relaxation of the atoms in all three dimensions. All forces used in the present calculations were derived from a first-principles interatomic pair potential obtained via pseudopotential theory. Several significant differences from the ordinary lattice statics results are noted, including the displacement field, Peierl's energy barrier, and the equilibrium core-center location.

Esterling, D. M.↗
NASA NTRS1978

Photocapacitive MIS infrared detectors

A new class of room-temperature infrared detectors has been developed through use of metal-insulator-semiconductor (MIS) or metal-insulator-semiconductor-insulator-metal (MISIM) slabs. The detectors, which have been fabricated from Si, Ge and GaAs, rely for operation on the electrical capacitance variations induced by modulated incident radiation. The peak detectivity for a 1000-A Si MISIM detector is comparable to that of a conventional Si detector functioning in the photovoltaic mode. Optimization of the photocapacitive-mode detection sensitivity is discussed.

Sher, A.↗
NASA NTRS1976

Two-electron bond-orbital model, 2

The two-electron bond-orbital model of tetrahedrally-coordinated solids is generalized and its application extended. All intrabond matrix elements entering the formalism are explicitly retained, including the direct overlap S between the anion and cation sp3 hybrid wavefunctions. Complete analytic results are obtained for the six two-electron eigenvalues and eigenstates of the anion-cation bond in terms of S, one-electron parameters V2 and V3, and two-electron correlation parameters V4, V5 and V6. Refined formulas for the dielectric constant and the nuclear exchange and pseudodipolar coefficients, as well as new expressions for the valence electron density, polarity of the bond and the cohesive energy, are then derived. The theory gives a good account of the experimentally observed trends in all properties considered and approximate quantitative agreement is achieved for the pseudodipolar coefficient.

Huang, C.↗
NASA NTRS1975

Two-electron bond-orbital model. I

The one-electron bond-orbital model of Harrison (1973) for tetrahedrally coordinated solids is modified to a two-electron model using a generalization of Falicov and Harris' (1969) method for treating the hydrogen molecule. Expressions for nuclear-exchange and pseudodipolar interactions are obtained in terms of bond-orbital model parameters. The eigenfunctions and eigenvalues of the Hamiltonian are employed along with standard perturbation theory to calculate the energy shifts resulting from the application of an external electric field and induced by the magnetic interaction between the nuclear spins and the bond-electron spins. The quantitative predictions of the derived formulas are examined for real semiconductors involving elements and compounds from periodic groups III, IV, and V. It is concluded that the present two-electron model makes it possible to assess the quantitative effects of electron correlation in the anion-cation bond for both nonmagnetic properties (electric susceptibility, dielectric constant) and magnetic properties (nuclear-exchange and pseudodipolar interactions) of various materials.

Huang, C.↗
NASA NTRS1975

Two-electron bond-orbital model, 1

Harrison's one-electron bond-orbital model of tetrahedrally coordinated solids was generalized to a two-electron model, using an extension of the method of Falicov and Harris for treating the hydrogen molecule. The six eigenvalues and eigenstates of the two-electron anion-cation Hamiltonian entering this theory can be found exactly general. The two-electron formalism is shown to provide a useful basis for calculating both non-magnetic and magnetic properties of semiconductors in perturbation theory. As an example of the former, expressions for the electric susceptibility and the dielectric constant were calculated. As an example of the latter, new expressions for the nuclear exchanges and pseudo-dipolar coefficients were calculated. A simple theoretical relationship between the dielectric constant and the exchange coefficient was also found in the limit of no correlation. These expressions were quantitatively evaluated in the limit of no correlation for twenty semiconductors.

Huang, C.↗