The cross-sectional sizes of the regularly patterned GaN nanorods (NRs) and InGaN/GaN quantum-well (QW) NRs of different heights and different hexagon orientations, which are grown on the patterned templates of different hole diameters, pitches, and crystal orientations, are compared. It is found that the cross-sectional size of the GaN NR, which is formed with the pulsed growth mode, is mainly controlled by the patterned hole diameter, and the thickness of the sidewall QW structure is mainly determined by the NR height. The cross-sectional size variation of GaN NR is interpreted by the quasi-three-dimensional nature of atom supply amount for precipitating a two-dimensional disk-shaped NR segment. The variation of the sidewall QW structure is explained by the condition of constituent atom supply in the gap volume between the neighboring NRs. Also, we compare the cathodoluminescence emission wavelengths among those samples of different growth conditions. Generally speaking, the QW NR with a smaller height, a larger cross-sectional size, or a larger pitch has a longer emission wavelength.

The growth of regularly patterned multi-section GaN nanorod (NR) arrays based on a pulsed growth technique with metalorganic chemical vapor deposition is demonstrated. Such an NR with multiple sections of different cross-sectional sizes is formed by tapering a uniform cross section to another through stepwise decreasing of the Ga supply duration to reduce the size of the catalytic Ga droplet. Contrast line structures are observed in either a scanning electron microscopy or transmission electron microscopy image of an NR. Such a contrast line-marker corresponds to a thin Ga-rich layer formed at the beginning of GaN precipitation of a pulsed growth cycle and illustrates the boundary between two successive growth cycles in pulsed growth. By analyzing the geometry variation of the contrast line-markers, the morphology evolution in the growth of a multi-section NR, including a tapering process, can be traced. Such a morphology variation is controlled by the size of the catalytic Ga droplet and its coverage range on the slant facets at the top of an NR. The comparison of emission spectra between single-, two-, and three-section GaN NRs with sidewall InGaN/GaN quantum wells indicates that a multi-section NR can lead to a significantly broader sidewall emission spectrum.

To achieve green emission from the sidewall non-polar quantum wells (QWs) of a GaN nanorod (NR) light-emitting diode, regularly patterned InGaN/GaN QW NR arrays are grown under various growth conditions of indium supply rate, QW growth temperature, and QW growth time for comparing their emission wavelength variations of the top-face c-plane and sidewall m-plane QWs based on photoluminescence and cathodoluminescence (CL) measurements. Although the variation trends of QW emission wavelength by changing those growth conditions in the NR structure are similar to those in the planar structure, the emission wavelength range of the QWs on an NR is significantly shorter than that in a planar structure under the same growth conditions. Under the growth conditions for a longer NR QW emission wavelength, the difference of emission wavelength between the top-face and sidewall QWs is smaller. Also, the variation range of the emission wavelength from the sidewall QWs over different heights on the sidewall becomes larger. On the other hand, strain state analysis based on transmission electron microscopy is undertaken to calibrate the average QW widths and average indium contents in the two groups of QW of an NR. The variation trends of the calibrated QW widths and indium contents are consistent with those of the CL emission wavelengths from various portions of NR QWs.

The growth of a two-section, core-shell, InGaN/GaN quantum-well (QW) nanorod- (NR-) array light-emitting diode device based on a pulsed growth technique with metalorganic chemical vapor deposition is demonstrated. A two-section n-GaN NR is grown through a tapering process for forming two uniform NR sections of different cross-sectional sizes. The cathodoluminescence (CL), photoluminescence (PL), and electrolumines-cence (EL) characterization results of the two-section NR structure are compared with those of a single-section NR sample, which is prepared under the similar condition to that for the first uniform NR section of the two-section sample. All the CL, PL, and EL spectra of the two-section sample (peaked between 520 and 525 nm) are red-shifted from those of the single-section sample (peaked around 490 nm) by >30 nm in wavelength. Also, the emitted spectral widths of the two-section sample become significantly larger than their counterparts of the single-section sample. The PL spectral full-width at half-maximum increases from ~37 to ~61 nm. Such variations are attributed to the higher indium incorporation in the sidewall QWs of the two-section sample due to the stronger strain relaxation in an NR section of a smaller cross-sectional size and the more constituent atom supply from the larger gap volume between neighboring NRs.

The growth and process of a regularly patterned nanorod (NR)- light-emitting diode (LED) array with its emission from sidewall non-polar quantum wells (QWs) are demonstrated. A pyramidal un-doped GaN structure is intentionally formed at the NR top for minimizing the current flow through this portion of the NR such that the injection current can be effectively guided to the sidewall m-plane InGaN/GaN QWs for emission excitation by a conformal transparent conductor (GaZnO). The injected current density at a given applied voltage of the NR LED device is similar to that of a planar c-plane or m-plane LED. The blue-shift trend of NR LED output spectrum with increasing injection current is caused by the non-uniform distributions of QW width and indium content along the height on a sidewall. The photoluminescence spectral shift under reversed bias confirms that the emission of the fabricated NR LED comes from non-polar QWs.