The influence of Mg doping on the nucleation of self-induced GaN nanowires

GaN nanowires were grown without any catalyst by plasma-assisted molecular beam epitaxy. Under supply of Mg, nanowire nucleation is faster, the areal density of wires increases to a higher value, and nanowire coalescence is more pronounced than without Mg. During nanowire nucleation the Ga desorption was monitored insitu by line-of-sight quadrupolemass spectrometry for various substrate temperatures. Nucleation energies of 4.0±0.3 eV and 3.2±0.3 eV without and with Mg supply were deduced, respectively. This effect has to be taken into account for the fabrication of nanowire devices and could be employed to tune the NW areal density

Influence of the adatom diffusion on selective growth of GaN nanowire regular arrays

Molecular beam epitaxy (MBE) on patterned Si/AlN/Si(111) substrates was used to obtain regular arrays of uniform-size GaN nanowires (NWs). The silicon top layer has been patterned with e-beam lithography, resulting in uniform arrays of holes with different diameters (d(h)) and periods (P). While the NW length is almost insensitive to the array parameters, the diameter increases significantly with d(h) and P till it saturates at P values higher than 800 nm. A diffusion induced model was used to explain the experimental results with an effective diffusion length of the adatoms on the Si, estimated to be about 400 nm. (C) 2011 American Institute of Physics. [doi:10.1063/1.3559618

Cathodoluminescence spectroscopy on selectively grown GaN nanowires

GaN nanowires (NWs) were grown selectively on Si(111) substrate without catalyst by plasma-assisted molecular-beam epitaxy under N-rich conditions. The selective growth was obtained using regular arrays of holes patterned in a silicon oxide layer on top of a thin AlN buffer. The optical properties of the selectively grown GaN NWs have been studied using cathodoluminescence (CL) spectroscopy. Both, CL spectra measured on NW ensembles and spatially resolved monochromatic images were investigated. From a comparison of morphology and CL studies it emerges that NW coalescence is responsible for the appearance of the defect related emission

Selective-area catalyst-free MBE growth of GaN nanowires using a patterned oxide layers

GaN nanowires (NWs) were grown selectively in holes of a patterned silicon oxide mask, by rf-plasma-assisted molecular beam epitaxy (PAMBE), without any metal catalyst. The oxide was deposited on a thin AlN buffer layer previously grown on a Si(111) substrate. Regular arrays of holes in the oxide layer were obtained using standard e-beam lithography. The selectivity of growth has been studied varying the substrate temperature, gallium beam equivalent pressure and patterning layout. Adjusting the growth parameters, GaN NWs can be selectively grown in the holes of the patterned oxide with complete suppression of the parasitic growth in between the holes. The occupation probability of a hole with a single or multiple NWs depends strongly on its diameter. The selectively grown GaN NWs have one common crystallographic orientation with respect to the Si(111) substrate via the AlN buffer layer, as proven by x-ray diffraction (XRD) measurements. Based on the experimental data, we present a schematic model of the GaN NW formation in which a GaN pedestal is initially grown in the hole