Electronic structure and the glass transition in pnictide and chalcogenide semiconductor alloys. Part II: The intrinsic electronic midgap states

Abstract

We propose a structural model that treats in a unified fashion both the atomic motions and electronic excitations in quenched melts of pnictide and chalcogenide semiconductors. In Part I (submitted to J. Chem. Phys.), we argued these quenched melts represent aperiodic $pp\sigma$-networks that are highly stable and, at the same time, structurally degenerate. These networks are characterized by a continuous range of coordination. Here we present a systematic way to classify these types of coordination in terms of discrete coordination defects in a parent structure defined on a simple cubic lattice. We identify the lowest energy coordination defects with the intrinsic midgap electronic states in semiconductor glasses, which were argued earlier to cause many of the unique optoelectronic anomalies in these materials. In addition, these coordination defects are mobile and correspond to the transition state configurations during the activated transport above the glass transition. The presence of the coordination defects may account for the puzzling discrepancy between the kinetic and thermodynamic fragility in chalcogenides. Finally, the proposed model recovers as limiting cases several popular types of bonding patterns proposed earlier, including: valence-alternation pairs, hypervalent configurations, and homopolar bonds in heteropolar compounds.

17 pages, 15 figures, revised version, final version to appear in J. Chem. Phys

References in corpus (13)

• Direct experimental evidence of a growing length scale accompanying the glass transition
• Theory of Structural Glasses and Supercooled Liquids
• Fragilities of Liquids Predicted from the Random First Order Transition Theory of Glasses
• Direct observation of molecular cooperativity near the glass transition
• Spatial correlations in the dynamics of glassforming liquids: Experimental determination of their temperature dependence
• Theory of Aging in Structural Glasses
• Barrier Softening near the onset of Non-Activated Transport in Supercooled Liquids: Implications for Establishing Detailed Connection between Thermodynamic and Kinetic Anomalies in Supercooled Liquids
• The Intrinsic Quantum Excitations of Low Temperature Glasses
• Direct Visualization of Two-State Dynamics on Metallic Glass Surfaces Well Below Tg
• Simulation of the physical properties of the chalcogenide glass As${}_2$S${}_3$ using a density-functional-based tight-binding method
• Stress distribution and the fragility of supercooled melts
• Electronic structure and the glass transition in pnictide and chalcogenide semiconductor alloys. Part I: The formation of the $pp\sigma$-network
• Comment on the ``Novel Isotope Effects Observed in Polarization Echo Experiments in Glasses''

Cited by in corpus (7)

• Theory of the Structural Glass Transition: A Pedagogical Review
• The chemical bond as an emergent phenomenon
• Electronic structure and the glass transition in pnictide and chalcogenide semiconductor alloys. Part I: The formation of the $pp\sigma$-network
• Self-consistent elastic continuum theory of degenerate, equilibrium aperiodic solids
• Temperature-driven narrowing of the insulating gap as a precursor of the insulator-to-metal transition: Implications for the electronic structure of solids
• Emergence of pseudo-time during optimal Monte Carlo sampling and temporal aspects of symmetry breaking and restoration
• First principles study of bandgap tuning in GePbSe