GaAs1-xBix growth on Ge: anti-phase domains, ordering, and exciton localization

Tadas Paulauskas,Mária Čaplovičová,Sandra Stanionytė,Bronislovas Čechavičius,Arnas Naujokaitis,Vaidas Pačebutas,Viliam Vretenár,Martynas Skapas,Evelina Dudutienė,Viktorija Strazdienė,Andrejus Geižutis,Arūnas Krotkus,Rafał Jakieła

doi:10.1038/s41598-020-58812-y

Tadas Paulauskas, Mária Čaplovičová + Show 11 more

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https://doi.org/10.1038/s41598-020-58812-y

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The dilute bismide alloy GaAs1-xBix has drawn significant attention from researchers interested in its fundamental properties and the potential for infrared optoelectronics applications. To extend the study of bismides, molecular-beam heteroepitaxy of nominally 1.0 eV bandgap bismide on Ge substrates is comprehensively investigated. Analysis of atomic-resolution anti-phase domain (APD) images in the direct-epitaxy revealed a high-density of Ga vacancies and a reduced Bi content at their boundaries. This likely played a key role in the preferential dissolution of Bi atoms from the APD interiors and Bi spiking in Ge during thermal annealing. Introduction of GaAs buffer on offcut Ge largely suppressed the formation of APDs, producing high-quality bismide with single-variant CuPtB-type ordered domains as large as 200 nm. Atomic-resolution X-ray imaging showed that 2-dimensional Bi-rich (111) planes contain up to x = 9% Bi. The anomalously early onset of localization found in the temperature-dependent photoluminescence suggests enhanced interactions among Bi states, as compared to non-ordered samples. Growth of large-domain single-variant ordered GaAs1-xBix films provides new prospects for detailed analysis of the structural modulation effects and may allow to further tailor properties of this alloy for optoelectronic applications.

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In contrast to a commonly employed Voronoi cell segmentation, the current approach allows for more accurate quantification of HAADF images that contain closely-spaced atomic-columns, e.g. GaAs (~1.4 Å)
The values of SCS primarily depend on the number and size of atoms in the column
The positions of Bi atoms along the column will influence the HAADF intensity and the SCS, since the electron probe intensity decreases with increasing specimen depth

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Introduction

Gaussian functions were fitted to the atomic-column positions. In contrast to a commonly employed Voronoi cell segmentation, the current approach allows for more accurate quantification of HAADF images that contain closely-spaced atomic-columns, e.g. The values of SCS primarily depend on the number and size of atoms in the column. Columnar distortions and the related broadening of SCS distributions are expected due to large Bi atoms, this effect is expected to be small compared to e.g., influence of point defects.

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