A complementary geometric model for the growth of GaN nanocolumns prepared by plasma-assisted molecular beam epitaxy

GaN based nanorods for solid state lighting

“…From that, the authors suggested that growth is not entirely suppressed without rotation, but it clearly appears to be a contributing factor. 39 A similar growth model of nanorod morphology depending on the MBE system geometry was also proposed by Galopin et al 40 In the last 2 years, the polarity of GaN nanorods became an attractive topic. [41][42][43][44][45] To determine the polarity of the GaN nanorods, many methods were employed, for example, convergent beam electron diffraction (CBED), 46,47 electron energy loss spectra (EELS), 48 probe Cs corrected transmission electron microscopy measurement, 49 Kelvin probe force microscopy (KPFM), 50 piezoresponse force microscopy (PFM), 51 coaxial impact-collision ion scattering spectroscopy (CAICISS) analysis, 52 circular photogalvanic effect (CPGE), 53 and wet chemical etching.…”

“…29 Foxon et al proposed a complementary geometrical growth model in which the rotation of the substrate is included. 39 This geometrical add-on to the existing GaN nanorod growth models predicts an enhanced growth rate in the vertical direction compared to the lateral growth rate of the rods. It also suggests a mechanism for the enhanced diffusion of gallium on the sidewalls of the rods even under strongly nitrogen-rich conditions.…”

“…Figures 12(a) and 12(b) show typical examples of GaN nanorods grown with and without rotation. 39 As shown in Fig. 12(a), wellaligned hexagonal-shaped GaN nanorods are usually observed with rotation, whereas very different aligned ''tadpoleshaped" GaN nanorods are obtained without rotation of the substrate ( Fig.…”

“…Therefore, the authors state that growth on the top surface can be described by classical MBE process, but on the sidewalls it is more akin to the migrationenhanced epitaxy (MEE) process. 39 This MEE process will enhance the Ga diffusivity even at strong N-rich conditions, consequently limits the lateral growth and promote the vertical growth of the nanorods. In addition, the different geometry leads to a significant difference in the arrival rates for molecules on the top and sidewalls, which results in a difference in growth rate, even in the absence of diffusion.…”

“…However, different polar surfaces induce different surface chemical reactivity, which is important, e.g., in the case of the impurity doping, 55,56 dopant incorporation, 57,58 surface reaction with gas, 59 and growth morphology of the GaN nanorods. 39,42 There are already numerous investigations reported on two-dimensional GaN layers with different polarities concerning these topics. However, such kind of investigation has not been extensively performed on nanorods, partly due to the difficulty in nanoscale characterization.…”