ABSTRACT
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.
ACKNOWLEDGMENTS
The authors gratefully acknowledge financial support through the National Science Foundation, Grant No. DMR-0909028 and the U.S. Army Research Office MURI program, Grant No. W911NF-10-1-0524. The authors also acknowledge the use of facilities in the LeRoy Eyring Center for Solid State Science and the John M. Cowley Center for High Resolution Electron Microscopy at Arizona State University.
