Understanding and reducing deleterious defects in the metastable alloy GaAsBi

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. Crystal defects can stop metastable alloys from working in novel devices, but a new study predicts ways to minimize such faults. When alloyed with bismuth atoms, gallium arsenide semiconductors could endow devices with unprecedented properties, such as high efficiency for high-power infrared laser diodes and temperature-insensitive performance for electronic devices. To reduce the defects caused by bismuth alloying including unwanted bismuth clusters that arise in typical fabrications, Guangfu Luo and Dane Morgan from the University of Wisconsin-Madison in the USA studied various possible alloy defects in the bismuth-containing gallium arsenide using density functional theory calculations. Their investigations revealed the dominant defect trap states and helped the team propose new ideas, including hydrogen passivation and new growth conditions, to reduce the populations of deleterious defects. Ab initio calculations reveal that defects AsGa, BiGa, AsGa+BiAs and BiGa+BiAs are the dominant minority-electron traps and defects VGa and VGa+BiAs are the dominant minority-hole traps in the metastable alloy GaAsBi grown under As-rich condition. Changing the growth away from the As-rich condition and/or using hydrogen passivation are suggested to reduce the deleterious effects of these defects.