Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO2 mask act as a template for GaAs-on-Si selective-area growth(SAG) of nanostubs 120 nm tall and ≤100 nm in diameter. We investigate the influence of growthparameters including substrate temperature and growth rate on SAG. Optimizing these parameters results in complete selectivity with GaAsgrowth only on the exposed Si(001). Due to the confined-geometry, strain and defects in the GaAs nanostubs are restricted in lateral dimensions, and surface energy is further minimized. We assess the electrical properties of the selectively grownGaAs nanostubs by fabricating heterogeneous p+–Si/n+–GaAs p–n diodes
