Highlights

Nanometer-scale Sharpness in Corner-overgrown Heterostructures

Scientific Achievement

A corner-overgrown GaAs/AlGaAs heterostructure was investigated with transmission and scanning transmission electron microscopy, demonstrating self-limiting growth of an extremely sharp corner profile of 3.5 nm width.  In the AlGaAs layers we observe self-ordered diagonal stripes, precipitating exactly at the corner, which are regions of increased Al content measured by an XEDS analysis.  A quantitative model for self-limited growth is adapted to the present case of faceted MBE growth, and the corner sharpness has been correlated with quantum-confined structures.  We note that MBE corner overgrowth maintains nm-sharpness even after microns of growth, allowing the realization of corner-shaped nanostructures.

Significance

The TEM/STEM/XEDS results demonstrate that the corner overgrowth technique yields extremely sharp self-limited corner profiles, justifying the assumption of a sharp corner potential in bent quantum Hall junctions [Grayson, et al., Phys. Rev. B 76 (2007)].  Compared to the lower resolution TEM images of self-ordered diagonal stripes shown in Biasiol, et al., Phys. Rev. B 65 )2002), the stripes observed in our corner-overgrown structure are a factor of 5 thinner.  Both the width of the self-limited profile and the Al adatom segregation observed in XEDS measurements on the AlGaAs layers can be estimated from a quantitative growth model with reasonable assumptions.  Due to the self-limitation it is possible to grow sharp corner profiles that are translated over microns of growth, where the minimum width is determined by the growth conditions.  This shows that the combination of MBE and corner overgrowth allows the precise control of one-dimensional quantum confinement, and justifies the assumptions of previous work of a sharp corner with a one-dimensional accumulation wire [Grayson, Physica E 22 (2004); Grayson, et al., Phys. Rev. B 76 (2007)].  This work has been submitted to Applied Physics Letters in 2008.

Performers

P. Cantwell and E. A. Stach (Purdue U.); M. Grayson (Northwestern U.); N. J. Zaluzec (Argonne-MSD)