Study on indium phosphide nanowires grown by metal organic chemical vapor deposition and coated with aluminum oxides deposited by atomic layer deposition

Semiconducting nanowires are promising materials for a variety of applications, many of which are in optoelectronics where their ability to use quantum confinement to tune transition energy levels and their ability to epitaxially grow on substrates with large lattice-mismatches enable unique opportunities. In addition, the large relative surface area of nanowire-based devices can be either a benefit as in, for example, sensor applications or challenges such as charge trapping, non-radiative recombination or Fermi-level pinning. In this study, indium phosphide nanowires grown by metal organic chemical vapor deposition were conformally coated with aluminum oxide by atomic layer deposition as a means of controlling the surface states within the indium phosphide region. Photoluminescence spectra from the coated nanowires show a strong blueshift and slight peak broadening as compared to uncoated nanowires despite their increased lateral dimension. This degree of blueshift is unlikely to have been caused by strain associated with the coating because of its relatively thin thickness (similar to 10 nm), and the x-ray diffraction profiles collected from the coated nanowires do not indicate the presence of substantial lattice deformation. It is more likely to be a result of altered chemical state at the surface; the uncoated nanowires have oxygen bound to both indium and phosphorus near the surface as confirmed in our X-ray photoelectron spectroscopy studies. Subsequent aluminum oxide deposition alters surface atomic bonding thereby modifying the states electronic responsible for optical properties in the nanowires.