Selective Area Epitaxy of GaN Nanowires on Si Substrates Using Microsphere Lithography: Experiment and Theory

Abstract

GaN nanowires were grown using selective area plasma-assisted molecular beam epitaxy on SiOx/Si(111) substrates patterned with microsphere lithography. For the first time, the temperature–Ga/N2 flux ratio map was established for selective area epitaxy of GaN nanowires. It is shown that the growth selectivity for GaN nanowires without any parasitic growth on a silica mask can be obtained in a relatively narrow range of substrate temperatures and Ga/N2 flux ratios. A model was developed that explains the selective growth range, which appeared to be highly sensitive to the growth temperature and Ga flux, as well as to the radius and pitch of the patterned pinholes. High crystal quality in the GaN nanowires was confirmed through low-temperature photoluminescence measurements.

Criterion for Selective Area Growth of III-V Nanowires

“…This work tries to fill the gap by establishing a model for the selectivity maps in terms of the material fluxes, temperature, and size and pitch of the openings. This work generalizes the earlier results obtained for the SAG of GaAs nanostructures [ 28 , 29 , 30 ], vertical GaN NWs [ 18 , 19 , 20 ], and planar GaAs and InAs NW networks [ 26 ], grown by MBE on different masked substrates. The influence of surface diffusion of group III adatoms and the minimum chemical potential required for nucleation on the growth selectivity is carefully investigated.…”

“…The VLS NWs usually grow perpendicular to (111) the substrate surface [ 3 , 6 , 8 , 9 , 10 ]. Regular arrays of vertical III-V and III-nitride NWs can also be obtained by catalyst-free SAG on different masked substrates, including Si, with lithographically defined pinholes [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Furthermore, SAG enables the fabrication of template-assisted, in-plane III-V NWs, nanomembranes, nanosheets, nanofins, and advanced NW networks of different architectures [ 21 , 22 , 23 , 24 , 25 , 26 , 27 ], some of which are promising for low-temperature transport physics [ 23 , 26 , 27 ].…”

“…The SAG approach consists of the preparation of a mask on a semiconductor substrate, the lithographic patterning of the mask, and the deposition of the III-V material, which should grow only in the mask openings. The SAG approach works equally well for MBE [ 15 , 18 , 19 , 20 , 23 , 26 ] and metal-organic chemical vapor deposition (MOCVD) [ 12 , 13 , 14 ] techniques. Compared to other growth methods, SAG offers much wider opportunities for the geometrical design of III-V nanostructures and complex networks based on such nanostructures.…”

“…Depending on the material combination, growth conditions and template geometry, four possible modes of SAG are possible: (i) true SAG inside the openings, without parasitic nucleation on the mask surface, (ii) random nucleation of III-V crystallites on the mask, along with single-crystalline growth inside the openings, (iii) random nucleation of group III droplets on the mask, and (iv) no growth on the mask and inside the openings [ 26 ]. Under group V-rich conditions typical for the SAG of GaN NWs, no Ga droplets can nucleate on the mask and the only possible parasitic structures are GaN crystallites or randomly oriented NWs [ 18 , 19 , 20 ]. In any case, the optimized SAG parameter window should correspond to the nucleation of the material inside the openings and the absence of parasitic nucleation on the mask [ 20 , 26 ].…”

“…Under group V-rich conditions typical for the SAG of GaN NWs, no Ga droplets can nucleate on the mask and the only possible parasitic structures are GaN crystallites or randomly oriented NWs [ 18 , 19 , 20 ]. In any case, the optimized SAG parameter window should correspond to the nucleation of the material inside the openings and the absence of parasitic nucleation on the mask [ 20 , 26 ]. Despite the importance of the growth selectivity issue, the comprehensive study of SAG, depending on the growth conditions and template geometry, is solely lacking in the literature.…”