Period-doubling reconstructions of semiconductor partial dislocations

Abstract

Atomic-scale understanding and control of dislocation cores is of great technological importance, because they act as recombination centers for charge carriers in optoelectronic devices. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90° partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling. The dimers in the single-period dislocation are able to interact, to form a dispersive one-dimensional band with deep-gap states. However, the inter-dimer interaction for the double-period dislocation becomes significantly reduced; hence, it is free of mid-gap states. The Ga core undergoes a further period-doubling transition to a quadruple-period reconstruction induced by the formation of small hole polarons. The competition between these dislocation phases suggests a new passivation strategy via population manipulation of the detrimental single-period phase. Theoretical simulations suggest a pathway toward reducing the population of efficiency-draining defects in gallium arsenide (GaAs) solar cells. Modern, multilayered light-harvesting devices can have lattice mismatches at interfaces where the crystals meet, and this can create dislocations - two-dimensional ribbons of atoms that disrupt the bulk crystal structure. Joongoo Kang from DGIST in Daegu, Korea, and collaborators at the USA's National Renewable Energy Laboratory have used sophisticated density-functional calculations to analyse GaAs dislocations that had different patterns of partnered atomic dimers. Repetitive ‘single-period’ dimers had deep gap states that degrade the optoelectronic performance. But less dense ‘double-period’ and newly discovered ‘quadruple-period’ structures can compete with the single-period phase and limit its influence — a passivation strategy that may be realized through shallow p-type doping of GaAs, suggest the researchers. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90° partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling, suggesting a new passivation strategy by biasing the competition between these phases through the tuning of the carrier density in the dislocation.