Bandgap Engineering of Nanowires:
In this project, we have developed a post-synthesis decomposition strategy for uniformly reducing the diameters of compound semiconductor nanowires. This strategy primarily employs the ballistic transport of metal adatoms on nanowire surfaces, a phenomenon exclusive to nanoscale semiconductor materials. This ballistic diffusion of metal adatoms on top of nanowire surfaces prevents their agglomeration into droplets during decomposition and hence the breakdown of nanowires into polycrystalline matter. In fact, the ballistic diffusion of metal adatoms allows for a layer-by-layer decomposition of compound semiconductors and the formation of compound semiconductor nanowires. Using this concept, we have reduced the diameters of GaN nanowires and obtained GaN quantum wires with diameters as small as 3-4 nm. This allowed for engineering the bandgaps of GaN from 3.4 eV to 3.9 eV. Pictorial illustrations of GaN nanowires and quantum wires are provided below.
Transmission electron micrographs of (a) as-obtained GaN nanowires and nanowires observed after (b) 6 minutes and (c) 10 minutes of decomposition in NH3. HR-TEM images of (d) an as-obtained nanowire and (e) a 3.2 nm GaN nanowire after decomposition indicating that the crystal structure and growth direction did not change. Reprinted with permission from Cryst. Growth Des. 11 (10), 4559-4564 (2011) - Copyright (2011) American Chemical Society.