J.C. Phillips

Topology of covalent non-crystalline solids I: Short-range order in chalcogenide alloys

The pronounced glass-forming tendencies of alloys of S and Se with Ge and/or As are discussed topologically. An atomic model is introduced which for predominantly covalent forces constitutes the first microscopic realization of Kauzmanns description of the glass transition as an entropy (not enthalpy or volume) crisis. The model contains no adjustable parameters and predicts the glass-forming tendency as a function of composition in excellent agreement with experiment. Several related properties, including phase diagrams, radial distribution functions and crystal structures are discussed in the context of chemical bonding and short-range order in the non-crystalline covalent networks of these materials.

Topology of covalent non-crystalline solids II: Medium-range order in chalcogenide alloys and ASi(Ge)

Abstract Characteristic order over distances of 15–30 A is indicated by various experiments on covalent non-crystalline solids. The data are reviewed and detailed structural models are developed containing 30–1000 atoms.

Heterojunction band discontinuities

The discontinuity ΔEc=0.56 eV in the conduction band edge at n‐CdS/p‐InP junctions is reported. This discontinuity and others are compared with photoemission data and with Van Vechten’s extension of these data to many tetrahedrally coordinated semiconductors. Agreement between measured discontinuities and theoretical predictions is very good. Predictions are made for band parameters pertinent to interfaces involving AIIBIVCV2 compounds with zinc blende, chalcopyrite, or wurtzite crystal structures.

Bonding constraints and defect formation at interfaces between crystalline silicon and advanced single layer and composite gate dielectrics

An increasingly important issue in semiconductor device physics is understanding of how departures from ideal bonding at silicon–dielectric interfaces generate electrically active defects that limit performance and reliability. Building on previously established criteria for formation of low defect density glasses, constraint theory is extended to crystalline silicon–dielectric interfaces that go beyond Si–SiO2 through development of a model that quantifies average bonding coordination at these interfaces. This extension is validated by application to interfaces between Si and stacked silicon oxide/nitride dielectrics demonstrating that as in bulk glasses and thin films, an average coordination, Nav, greater than three yields increasing defective interfaces.

Microscopic origin of anomalously narrow Raman lines in network glasses

Abstract Molecular models for the mysterious 495 and 606 cm −1 “defect” lines in the Raman spectra of g-SiO 2 are discussed in the context of a general theory and a survey of a wide range of experimental data, including hydroxylation, neutron bombardment, and isotope shifts.

Broken chemical order and phase separation in GexSe1−x glasses

Abstract The trend of broken chemical order in GexSe1−x glasses displays a minimum at x = 3 8 ; as well as at x = 1 3 ;. The composition dependence of site populations determined by Mossbauer spectroscopy can be quantitatively understood in terms of molecular phase separation in these glasses. The proposed molecular phases and their morphologies are discussed in terms of a quasi-equilibrium free energy for rapidly quenched-melts. It is shown that this general approach provides a microscopic basis for understanding the overall glass forming tendency not only in binary but also in many ternary chalcogenide glasses.

Minimization of dangling bond defects in hydrogenated silicon nitride dielectrics for thin film transistors (TFTs)

Abstract Plasma deposited hydrogenated amorphous silicon nitride alloys are the preferred gate dielectric for amorphous silicon thin film transistors (TFTs). This paper identifies for the first time a correlation between the relative concentrations of silicon, [Si], nitrogen, [N] and hydrogen, [H], in these alloys, and optimization of TFT performance. The TFT electron channel mobility, μe, has been shown to be a function of the NH3 to SiH4 source gas ratios which determine [Si], [N] and [H] in plasma deposited dielectrics. Optimized performance with μe∼1.5 cm2 V−1 s, has been demonstrated for remote plasma deposited nitrides with [Si]∼0.28, [N]∼0.42 and [H]∼0.3. This alloy composition has approximately the same average number of (i) bonds per atom, 〈N〉, and (ii) bonding constraints per atom, 〈C〉, as thin film SiO2, and also forms a continuous random network with a low density of defect states accounting for optimized TFT performance.

Solid solution formation in the systems CuMIIIX2-AgMIIIX2 where MIII=Al, Ga, In and X2=S, Se

Abstract A study of solid solution formation in the systems CuAlX2-AgAlX2, CuGaX2-AgGaX2 and CuInX2-AgInX2, where X=S, Se, has shown that when MIII=Al and Ga, CuMIIIX2 and AgMIIIX2 were not completely miscible. The CuInX2-AgInX2 system, however, showed complete solid solubility. The limits of solid solubility are explained in terms of the c/a ratio, and the internal atomic coordinate u. The lattice constant a is a linear function of composition, while c bows upwards. This behavior is also discussed in terms of trends in 2-c/a.

Reversible reconstruction and crystallization of GeSe2 glass

Abstract Absorption of photons at low power levels below the band edge reversibly alters the molecular structure of GeSe 2 glass. Several stages of ordering, including the formation of microcrystallites, have been observed by Raman scattering. The absorbed photons systematically increase the chemical ordering of the glass by breaking like-atom bonds and replacing them with GeSe bonds.

Topology of covalent non-crystalline solids III: Kinetic model of the glass transition

Abstract The temperature dependence of the viscosity of glass-forming materials is derived from the assumption of constant configurational specific heat in the supercooled liquid by using rate theory and a specific structural model. It is argued that the model is less restrictive than appearances suggest. It may be qualitatively corrent for many glass-forming systems, although it has been designed specifically for chalcogenide alloy glasses.