Optimization of metamorphic buffers for MBE growth of high quality AlInSb/InSb quantum structures: Suppression of hillock formation
Dislocation filtering in metamorphic buffers is studied with AFM and STEM.
Method for spiral growth suppression and hillocks elimination is reported.
Atomically flat, defect-free surfaces for InSb top-down nanostructures are obtained.
The optimization of metamorphic buffers for InSb/AlInSb QWs grown on GaAs (001) substrates is presented. With increasing surface offcut angle towards direction, the interaction of spiral growth around threading dislocations (TDs) with the offcut-induced atomic steps leads to a gradual change in the morphology of the AlSb buffer from one dominated by hillocks to that exhibiting near-parallel steps, and finally to a surface with increasing number of localized depressions. With the growth conditions used, the smoothest AlSb surface morphology was obtained for the offcut angles range of 0.8–1.3°. On substrates with 0° offcut, subsequent 3 repeats of Sb/Sb interlayers reduces the TD density of AlSb buffer by a factor of 10, while 70 times reduction in the surface density of TD-related hillocks is observed. The remaining hillocks have rectangular footprint and small facet angles with respect to GaAs (001) surface: 0.4° towards direction and 0.7° towards  direction. Their triangular-shaped sidewalls with regularly spaced atomic steps show occasional extra step insertion sites, characteristic of TD outcrops. Many of the observed sidewalls are dislocation free and offer atomically smooth areas of up to 1μm2, already suitable for high-quality InSb growth and subsequent top-down fabrication of InSb nanowires. It is proposed that the sidewalls of the remaining hillocks offer local vicinal surfaces with atomic step density optimal for suppression of TD-induced spiral growth, thus providing the important information on the exact substrate offcut needed to achieve large hillock-free and atomically smooth areas on AlInSb metamorphic buffers.