Atomic force microscopy of III-V nanostructures in air

Atomic force microscopy (AFM) in air was used to study the (<(1)over bar 10>) and (001) surfaces of III-V-heterostructures, grown by organometallic chemical vapor deposition (OMCVD) on planar or patterned (001) substrates. Topographies of the grown (001) surfaces as well as of ((1) over bar 10) cleaved cross-sections were examined. Although contamination and oxidation processes in air are expected to modify the structure of the surfaces in both cases, the AFM height profile, taken at constant force, yields structural information down to the monolayer level. On a cleaved surface of a III-V-heterostructure exposed to air, a natural oxide layer starts to grow immediately after cleaving. The growth rate of the oxide depends on the material composition and thus the topography can be used to map the composition within the scanned area. We used the AFM to characterize the growth on oxide on AlxGa1-xAs and GaAs-layers, and performed imaging of AlxGa1-xAs/GaAs heterostructures utilizing the topography for composition identification. On the (001) surface of GaAs and InP, exposed to air, we observed terraces, separated by steps of monolayer height, and exhibiting a staircase-like morphology. Average terrace size and direction depend on the misorientation of the substrate. Formation of isolated growth islands, probably due to spontaneous nucleation, was also observed.