Abstract
Technological applications of novel metastable materials are frequently inhibited by abundant defects residing in these materials. Using first-principles methods, we investigate the defect thermodynamics and phase segregation in the technologically important metastable alloy GaAsBi. Our calculations predict defect energy levels in good agreement with those from numerous previous experiments and clarify the defect structures giving rise to these levels. We find that vacancies in some charge states become metastable or unstable with respect to antisite formation, and this instability is a general characteristic of zincblende semiconductors with small ionicity. The dominant point defects that degrade the electronic and optical performances are predicted to be AsGa, BiGa, AsGa+BiAs, BiGa+BiAs, VGa and VGa+BiAs, of which the first four and last two defects are minority-electron and minority-hole traps, respectively. VGa is also observed to have a critical role in controlling metastable Bi supersaturation by mediating Bi diffusion and clustering. To reduce the influences of these deleterious defects, we suggest shifting the growth away from an As-rich condition and/or using hydrogen passivation to reduce the minority-carrier traps. We expect this work to aid in the applications of GaAsBi for novel electronic and optoelectronic devices and to illuminate the control of deleterious defects in other metastable materials.
Highlights
The metastable alloy GaAsBi has been intensely studied since its first successful fabrication by metalorganic vapor phase epitaxy in 19981 and by molecular beam epitaxy in 20032 owing to three key advantages over other GaAs-based compounds
We find that vacancies in some charge states become metastable or unstable with respect to antisite formation, and this instability is a general characteristic of zincblende semiconductors with small ionicity
We address the following essential questions related to the defects in GaAsBi: What are the primary intrinsic point defects, and how do they interact to form pair defects under equilibrium conditions? How do the defects affect the minority-carriers? Which defects mediate the formation of Bi-rich clusters during thermal annealing? how can one reduce the deleterious effects of the dominant defects? Our results are predominantly based on the University Avenue, Madison, WI 53706, USA
Summary
The metastable alloy GaAsBi has been intensely studied since its first successful fabrication by metalorganic vapor phase epitaxy in 19981 and by molecular beam epitaxy in 20032 owing to three key advantages over other GaAs-based compounds. Bi atoms strongly increase the spin-orbit splitting of GaAsBi, and for Bi contents near 10%, it is expected to totally suspend one type of Auger recombination,[3,5] which induces the serious ‘efficiency droop’ in high-energy light-emitting diodes and laser diodes. These advantages indicate that GaAsBi would provide a major improvement in many semiconductor devices as long as high-quality materials with a significant Bi content can be obtained
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