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Full-Text Articles in Physics
Boron Alloying In Gan, Gus L. W. Hart, Laurian Escalanti
Boron Alloying In Gan, Gus L. W. Hart, Laurian Escalanti
Faculty Publications
Using first-principles calculations in the local density approximation, we studied effects of adding up to 6% boron to zinc-blende GaN. We found that the band gap increases monotonically with boron incorporation, in agreement with experiment. A composition-independent band-gap bowing parameter of 4.30 eV was determined, and proved to be large compared to bowing for other mixed cation systems. The formation enthalpy of mixing, ΔH, was determined for BxGa1-xN, BxGa1-xAs, and GaAs1-xNx. A comparison of enthalpies indicates that the production of BxGa1-xN films with boron concentrations of at least 5% may be possible.
Ordering Tendencies In Octahedral Mgo-Zno Alloys, Gus L. W. Hart, Mahdi Sanati, Alex Zunger
Ordering Tendencies In Octahedral Mgo-Zno Alloys, Gus L. W. Hart, Mahdi Sanati, Alex Zunger
Faculty Publications
Isostrutural II-VI alloys whose components are either rocksalt stable (e.g., CaO-MgO) or zincblende stable (e.g., ZnS-ZnSe) are known to be thermodynamically unstable at low temperatures, showing a miscibility gap and no bulk ordering. In contrast, we show that heterostructural MgO-ZnO is stable, under certain conditions, in the sixfold-coordinated structure for Zn concentrations below 67%, giving rise to spontaneously ordered alloys. Using first-principles calculations, we explain the origin of this stability, the structures of their low-temperature ordered phases, short-range-order patterns, and their optical band-gap properties.
Origins Of Nonstoichiometry And Vacancy Ordering In Sc1-X□Xs, Gus L. W. Hart, Alex Zunger
Origins Of Nonstoichiometry And Vacancy Ordering In Sc1-X□Xs, Gus L. W. Hart, Alex Zunger
Faculty Publications
Whereas nearly all compounds AnBm obey Dalton's rule of integer stoichiometry (n:m, both integer), there is a class of systems, exemplified by the rocksalt structure Sc1-x□xS, that exhibits large deviations from stoichiometry via vacancies, even at low temperatures. By combining first-principles total energy calculations with lattice statistical mechanics, we scan an astronomical number of possible structures, identifying the stable ground states. Surprisingly, all have the same motifs: (111) planes with (112) vacancy rows arranged in (110) columns. Electronic structure calculations of the ground states (identified out of ~3 × 10^6 structures) reveal the remarkable origins of nonstoichiometry.