In the past few years, tremendous progress has been demonstrated on epitaxial growth and processing of group III nitride nano‐ and microrods (NAMs). This has also enabled the fabrication of optoelectronic devices based on NAMs as active elements. However, their efficiency is still far behind the performance of conventional GaN‐based light emitting diodes (LEDs). This Review presents the most recent activities on the growth and processing of NAMs exhibiting a core–shell geometry, i.e. structures which consist of an active region shell layer wrapped around a three‐dimensional (3D) core, which allow for an enormous increase in active area compared to planar technology. The most common growth approaches using metalorganic vapour phase epitaxy are described and evaluated with particular regard to their potential for solid state lighting applications. Examples for the unique properties of 3D NAMs are presented including their excellent crystalline quality. Furthermore, factors limiting the overall performance of 3D core–shell LEDs are revealed and the potential of overcoming these limitations are discussed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this theoretical study, we investigate both electronic and optical properties of core–shell InGaN nanorods (NRs) for light emitting diodes (LEDs). These structures feature active layers wrapped around high aspect ratio NR cores, thus allowing for an enormous increase in active area. Hence, efficiency may be increased by operating at lower carrier densities, mitigating efficiency droop known to limit conventional InGaN LEDs. Due to poor conductivity of the outer pGaN shell, current spreading along the entire NR length is challenging and requires an additional cover of transparent conductive oxide in order to fully exploit the active area. At the same time, quantum wells (QWs) on core–shell NRs are grown on m‐plane rather than conventional c‐plane GaN facets. The calculations show that the absence of piezoelectric fields on these non‐polar facets results in strong reabsorption of the emitted photons. A comprehensive numerical model is applied, linking internal quantum efficiency (IQE) and light extraction via the process of photon recycling. In summary, increasing optical absorption and photon recycling losses limit extraction efficiency. While this partially compensates the gain in IQE with increasing active area, a net improvement of the external quantum efficiency (EQE) of +10% is achievable by the proposed design of a novel core–shell NR LED.

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We present a numerical optimization of nanorod geometries with respect to the optical properties of an electrically driven LED emitting in the green spectral range. It is shown that an overall Purcell enhancement as well as directional emission can be achieved at an emission wavelength of 550 nm with nanorods of 110 nm radius. Position‐controlled growth on patterned substrates demonstrates that the required dimensions are accessible by varying growth parameters and growth time in a large volume MOVPE reactor. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)