GaN nanowires with InGaN quantum wells (QW) were grown on heated Si(111) substrates by molecular beam epitaxy (MBE) using elemental Ga and In and a radio-frequency-plasma N2 source. The growth procedures and the morphology of these nanowires have been described previously. Most nanowires were approximately 1000 nm long and 60 to 130 nm wide with hexagonal cross-sections. The nanowires were single crystals of the wurzite structure that grow along the <0001> direction. The InGaN QWs were produced by introducing In for a brief time interval during the growth. The In concentration in the QWs ranged from 12 to 15 atomic percent, as determined by energy dispersive spectroscopy in both the TEM and SEM (transmission and scanning electron microscopes). Individual nanowires were collected onto holey carbon TEM grids by dragging the grids across the substrate. Fourier transform (FT) analysis of <0002> and <101 ̅0> lattice images of the QW region showed a 4 to 10 % increase of the c-axis lattice spacing, across the full specimen width, and essentially no change in the a-axis value. The magnitude of the changes in the c-axis lattice spacing far exceeds values that would be expected considering the measured In concentration using a linear Vegard's law for GaN InN. Therefore the increases are considered to represent a strain of the lattice in the <0001> direction. Colored lattice images providing a visual representation of the location and extent of the strained regions were produced by constructing inverse FT (IFT) images from selected regions in the FT covering the range of c-axis lattice parameters in and near the QW. The magnitudes of the measured strains in the InGaN QW are consistent with the assumption that the InGaN region has the volume that it would have if unconstrained by the surrounding GaN regions, but is distorted so that only the lattice parameter along the nanowire axis is different from that of GaN.
Conference Dates: April 13-17, 2009
Conference Location: San Francisco, CA
Conference Title: 2009 Materials Research Society Spring Meeting
Pub Type: Conferences
gallium, indium, lattice, nitride