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

Abstract

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 (dh) and periods (P). While the NW length is almost insensitive to the array parameters, the diameter increases significantly with dh 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.

Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy

“…The largest print found without any nanorod, or GaN crystal inside is around 450 nm in size, which can be recognized as the diffusion length of Ga adatoms on the Si/SiN surface. This size is comparable with reported experimental observations of 400-500 nm, 10,13 but much larger than the theoretically predicted value of 100 nm. 35 In order to further explore the mechanism behind the nucleation and growth, a large print area with multiple rods is selected for extended observation (Figure 3(a)).…”

“…For the reported growth of GaN nanorods, the nucleation density and aspect ratio of nanorods were controlled by the substrate temperature and III/V ratio, [4][5][6][7] which also affect the crystal quality, the growth rate, and the morphology of rods. On the other hand, many groups have reported on the control of the rod density and position by the fabrication of a mask of a patterned oxide, 8 SiNx, 9 Si, 10 or metal. 11,12 The technologies of e-beam-lithography, UV lithography, or focused ion-beam technology are often used to selectively grow GaN nanorods.…”

“…Direct evidence other than the rod-polarity is therefore needed to clarify the origin of the nucleation mechanism. The mechanism behind the rod elongation is generally agreed to be due to the diffusion induced mechanism 10,[24][25][26] and the conventional migration-enhanced epitaxy (MEE) 27 on the sidewall of the rod. The diffusion flux of the adatoms from the sidewall to the top is comparable to the deposition rate.…”

“…Spontaneously formed multiple nanorods were grown and successively merged into larger rods. 9,10 The uniformity of the rod diameters decreases drastically for mask openings <300 nm due to the technical limitation of e-beam lithography and etching. 9 Therefore, an understanding of the nucleation mechanism is crucial.…”

GaN based nanorods for solid state lighting

“…79 The role of adatom diffusion on the geometry of GaN nanorods during selective area growth was discussed. 80 Bengoechea-Encabo et aldemonstrated successful GaN nanorod growth on patterned GaN/sapphire templates with a Ti mask layer. 73 They showed that the local V/III ratio, pattern geometry, and growth temperature are critical parameters to achieve vertical GaN nanorod growth.…”