Growth, characterization and device application of gallium nitride nanowires grown by MOCVD without catalyst

Wide bandgap, III-nitride nanowires are of interest both for their individual quantum-confinement properties and also as ordered arrays, where for example, they can be used to form photonic crystals. GaN-based nanowire preparation is usually based on the vapor-liquid-solid (VLS) growth mechanism with the use of an additional metal catalyst that can also be a contaminant.; Two approaches are reported for the growth of vertically aligned GaN nanowire arrays by metalorganic chemical vapor deposition (MOCVD) using standard precursors and no additional catalyst. In both cases nanowires were grown selectively through a patterned silicon nitride growth mask that had been deposited on previously grown GaN/SiC, GaN/sapphire and GaN/Si(111) structures. The position, size and spacing of GaN nanowire array are precisely controlled by the growth mask. Our first approach is based on MOCVD growth using a thick SiNx mask, essentially this growth creates nanowires by confining the growth to within cylindrical holes inside the thick SiNx mask. We refer to this as the confined growth nanowire process. The second approach relies on a special pulsed MOCVD growth and will be referred to as the pulsed growth nanowire process. The growth mask was patterned by interferometric lithography (IL) and dry etching, to form a hexagonal array of open windows with a pitch ranged from 300 nm to 2 mum and a diameter ranged from 150 nm to 700 nm. These two types of nanowires were characterized thoroughly and preliminary device applications were also investigated.; In the first nanowire process MOCVD GaN was grown selectively through a thick (850 nm) silicon nitride growth mask. Growth was completely confined within the deep silicon nitride windows and this forced the GaN growth to adopt a columnar form until it emerged from the growth mask. The base of these GaN nanowires was cylindrical with no faceting, while their tip showed the typically observed facetted, hexagonal pyramid form bounded by {lcub}1 101{rcub} facets.; The second GaN nanowire process uses a thin (30 nm), patterned silicon nitride growth mask. Ordered arrays of uniform GaN nanowires were achieved by using a low V/III ratio during MOCVD growth. The GaN nanowires in this case exhibited a stable, hexagonal cross-section, which was bounded by vertical {lcub}1101{rcub} facets, and this cross-section remained unchanged for longer or shorter growth times. Nanowires over 20 pm long with a diameter of 200 mil were achieved at a vertical growth rate of 2.4 mum /hr.; We believe this is the first time that ordered arrays of uniform GaN nanowires have been grown without the help of catalysts and these GaN-based nanowires show great potential for optoelectronic applications.