Growth of GaN free-standing nanowires by plasma-assisted molecular beam epitaxy: structural and optical characterization

Abstract

This paper reports on the growth, structural and optical properties of GaN free-stranding nanowires synthesized in catalyst-free mode on Si(111) substrate by plasma-assisted molecular beam epitaxy. Cylindrical nanowires with a hexagonal cross-section defined by {1010} planes and diameters down to 20 nm were observed. The nanowire length increases as a function of their diameter, following the Gibbs-Thomson expression. The growth rate in the lateral direction was studied using thin AlN marker layers showing that the lateral over axial growth rate ratio can be tuned from ∼1% to ∼10% by changing the III/V flux ratio, with the lateral growth remaining homogeneous along the NW axis. Nanowire ensembles showed a strong near band edge photoluminescence up to room temperature. Low-temperature micro-photoluminescence from a single wire is peaked at 3.478 eV with broadening of 6-10 meV. This emission is similar to the luminescence of nanowire ensembles, which demonstrates strain homogeneity from wire to wire. The optical properties along the wire axis probed by micro-cathodoluminescence were found to be uniform, with no evidence of a higher defect density in the bottom part of the nanowires next to the Si substrate.

Optical properties of GaN nanorods grown catalyst‐free on r‐plane sapphire

“…The D 0 X A recombination dominates the spectrum at low temperatures with a linewidth of 1.2 meV at T = 4 K, comparable to the value reported for strain-free GaN (~ 1 meV) [15] and high quality GaN nanowires [19]. This linewidth is distinctly smaller than the values reported in literature for catalystfree GaN nanowires on Si(111) between ~3.1 meV [9] and 9 meV [10]. Figure 2a shows the ensemble emission at T = 4 K in comparison to the measurement performed at 50 K. The higher energy emission lines, already ascribed to the X A and X B free-exciton recombination, are more pronounced relative to the D 0 X A because of the thermal ionization of the shallow donor-bound exciton.…”

Effects of morphologies on the field emission characteristics of GaN nanorods grown on Si (001) by MBE

“…This result agrees with the results reported over the last few years [9,10], which shows that GaN nanorods grow both axially and laterally with growth time.…”

GaN based nanorods for solid state lighting

“…Many groups claimed dislocation-free GaN nanorods growth by TEM analysis. [95][96][97] However, TEM is a locallyresolved method; it is generally hard to derive the global, statistically averaged properties of single nanorods. On the other hand, the dislocation density within GaN nanorods is expected to depend on both the lattice/thermal expansion mismatches and the diameter of the GaN nanorods.…”