Fabrication and analysis of GaN nanorods grown by MBE

Abstract

GaN nanorods were grown on c-plane sapphire substrates under N-rich conditions by plasma-assisted molecular-beam epitaxy. Scanning electron microsopy revealed densely packed nanorods of hexagonal cross section with diameters ranging from roughly 40 to 100 nm. Atomic force microscopy indicated that the rods protruded 50 to 75 nm above the average height of the surface. Transmission electron microscopy (TEM) showed that the nanorods were approximately 1.4 micrometers in length but an accurate measurement of the rod separation was difficult to assess. Contrary to expectations for GaN grown under N-rich conditions, a high density of basal plane stacking faults were not revealed in TEM under typical imaging conditions. X-ray diffraction using the (0002), (0004), (0006) reflections yielded c = 0.5188 ± 0.0002 nm and a = 0.3188 ± 0.0004 nm. Low temperature photoluminescence and cathodoluminescence showed broad near-bandgap emission around 3.4 eV that shifted to the blue with reduced temperature in the usual manner, and the presence of a similarly blue-shifting peak near 3.2 eV. The spectra were deconvolved using nine lineshape functions revealing 2 phonon replicas asssociated with the peak near 3.2 eV. Room temperature spectroscopic reflection fited to the standard Aspnes thirdderivative lineshape function yielded a transition energy of 3.407 eV for the A exciton and 3.490 eV for the B+C excitons (not spectrally resolved). Both the x-ray and photoreflectance results indicate that the nanorods are fairly relaxed.

A Review of Mechanical and Electromechanical Properties of Piezoelectric Nanowires

“…A feature that may be important in the mechanical characterization of failure properties of GaN is the presence of planar defects, such as stacking faults. The precise extent to which these defects are widespread among the different synthesis methods is unknown, although they seem to be less important in molecular beam epitaxy,76 while they have been clearly observed for CVD synthesis 20. The characterization of the mechanically‐tested structures for this type of defects, preferably in situ the TEM, will be critical in unambiguously characterizing the failure properties of GaN nanowires.…”

Molecular beam epitaxial growth of high-quality GaN nanocolumns

“…Despite technological advances in group III-nitride device development, the effects of defects in these materials, mainly due to a lack of native GaN substrates, is an ongoing concern. Recently, however, many epitaxial nanostructures have been reported that are composed of relatively defect-free Ga x Al 1Àx N crystals with nanometer widths, and lengths on the order microns [1][2][3][4][5][6][7][8][9][10]. While these nanocolumns (NCs) take on a variety of aerial densities and the results span a range of growth parameters and epitaxial techniques, a key condition is that NC formation requires epitaxial growth under nitrogen-rich conditions-resulting in reduced Ga surface diffusion.…”

Optical and structural study of GaN nanowires grown by catalyst-free molecular beam epitaxy. I. Near-band-edge luminescence and strain effects

“…In a companion article 17 ͑Part II͒, lower-energy PL and CL peaks ascribed to defect-related levels are discussed; in addition, CL quenching induced by extended electron-beam irradiation is examined. In both parts of this study, our results are compared to the literature on luminescence spectroscopy of GaN, including studies of MBE-grown nanowires 5,6,18 quasisubstrates, [19][20][21][22][23][24] and the review by Reshchikov 13 of defectrelated luminescence in a range of samples.…”