Molecular beam epitaxy using bismuth as a constituent in InAs and a surfactant in InAs/InAsSb superlattices

Alloying bismuth with InAs provides a ternary material system near the 6.1 Å lattice constant, which covers the technologically important mid- and long-wavelength infrared region. One challenge for this material system is that it is not straightforward to incorporate bismuth into the bulk InAs lattice, since bismuth has a tendency to surface-segregate and form droplets during growth. In this work, the conditions for InAsBi growth using molecular beam epitaxy are explored. A growth window is identified (temperatures ⪞ 270 °C, V/III flux ratios 0.98 ⪝ As/In ⪝ 1.02, and Bi/In ≅ 0.065) for droplet-free, high-quality crystalline material, where InAsBi layers with compositions of up to 5.8% bismuth (nearly lattice-matched to GaSb) are attained. The structural quality of InAsBi bulk and quantum well samples is evaluated using x-ray diffraction and transmission electron microscopy. The optical quality is assessed using photoluminescence, which is observed from quantum well structures up to room temperature and from thick, low Bi-content bulk layers at low temperatures. Bismuth is also used as a surfactant during the growth of InAs/InAsSb superlattices at 430 °C where it is observed that a small bismuth flux changes the surface reconstruction of InAs from (2×1) to (1×3), reduces the sticking coefficient of antimony, results in a slight increase in photoluminescence intensity, does not significantly incorporate, and does not alter the surface morphology.