Controlling morphology and optical properties of self-catalyzed, mask-free GaN rods and nanorods by metal-organic vapor phase epitaxy

Abstract

Ductile relaxation in cracked metal-organic chemical-vapor-deposition-grownA simple self-catalyzed and mask-free approach will be presented to grow GaN rods and nanorods based on the metal-organic vapor phase epitaxy technique. The growth parameter dependent adjustment of the morphology of the structures will be discussed. Rods and nanorods with diameters reaching from a few lm down to 100 nm, heights up to 48 lm, and densities up to 8Á10 7 cm -2 are all vertically aligned with respect to the sample surface and exhibiting a hexagonal shape with smooth sidewall facets. Optical properties of GaN nanorods were determined using cathodoluminescence. It will be shown that the optical properties can be improved just by reducing the Ga precursor flow. Furthermore, for regular hexagonal shaped rods and nanorods, whispering gallery modes with quality factors up to 500 were observed by cathodoluminescence pointing out high morphological quality of the structures. Structural investigations using transmission electron microscopy show that larger GaN nanorods (diameter > 500 nm) contain threading dislocations in the bottom part and vertical inversion domain boundaries, which separate a Ga-polar core from a N-polar shell. In contrast, small GaN nanorods ($200 nm) are largely free of such extended defects. Finally, evidence for a self-catalyzed, Ga-induced vapor-liquid-solid growth will be discussed. V C 2013 AIP Publishing LLC. [http://dx

Selective‐area growth of doped GaN nanorods by pulsed‐mode MOCVD: Effect of Si and Mg dopants

“…The increase of the vertical growth rate with increasing Si flow rate is in agreement with similar behavior reported previously . It is noteworthy that a lower V/III ratio should generally be adopted for growing nanorods via MOCVD compared with for normal GaN epilayers . The Ga‐rich condition not only suppresses strong H 2 passivation on the semipolar planes, but also leads to the ready formation of Ga‐bilayers, indicating enhanced growth along the axial c ‐direction .…”

III-nitride core–shell nanorod array on quartz substrates

“…For the following reasons, we strongly believe that the section of different brightness originated from polarity inversion between the Ga and N polarities: (1) as confirmed by repeated FFT trials of several spots inside the GaN NRs, the (0001) or oriented wurtzite GaN structures were highly homogenous (lower right of Fig. 6a); (2) the terminated surfaces on the topmost region had flat (left side) and tilted (right side) facets, reflecting the flat top terminations of N-polar GaN and the semipolar surfaces of Ga-polar GaN under the common SAG, respectively363738; (3) when the top surfaces of grown GaN NRs were partially etched by a KOH solution (4 M at 44 °C), a mixed polarity was observed (Fig. 6c; see Supplementary Fig.…”

Polarity‐ and Site‐Controlled Metal Organic Vapor Phase Epitaxy of 3D‐GaN on Si(111)

“…The reason for this is also an increased density of nucleation points for sample A, resulting in the growth of small 3D‐GaN (<100 nm) in‐between the structures. Due to Ostwald ripening at the used MOVPE‐parameters there is no seed visible for any nucleation point, but an increased layer roughness emerged. The dominant growth of Me‐polar GaN is visible for both samples, which indicates that the chosen MOVPE parameters promoted Me‐polar growth rather than N‐polar growth.…”

“…The sooner the inner seeds merge, the faster the GaN grows at this position. This process is well known as Ostwald ripening . We assume that the size, the number, and the polarity of the inner seeds determine the Ostwald ripening process and therefore the size of the seeds or islands after growth.…”