An inadvertent error has occurred in the derivation of the theoretical ratio of mand a-plane segment lengths for the GaN equilibrium crystal shape using the Wulff-plot in projection along 0001 as shown in figure 7(b) of our paper (2013 New J. Phys. 15 053045). A value of s = 2.4 was reported, however, the correct value is s = 1.8. Within the accuracy of the measurement, the experimentally derived value of 2.2(4) is in agreement with this corrected value.Abstract. Selective area growth of GaN nanocolumns (NCs) by molecular beam epitaxy on laser ablated pre-patterned GaN(0001) templates is shown to provide regular arrays of Ga-polar NCs. The Ga diffusion-assisted growth mechanism is analyzed and the experiments suggest that the effective growth conditions vary with the height of the NCs due to Ga diffusion on the mask and the NC sidewalls, ranging from N-rich up to stoichiometry. The obtained morphology with semipolar facets at the tip is discussed within the framework of equilibrium thermodynamics, which provides a consistent picture also for the growth of N-polar NCs with flat tips. The structural investigation reveals almost defect-free semipolar {1102} GaN facets at the top of the NCs, which is known to be a promising way of producing templates for nanoscale semipolar GaN-based heterostructures. Almost no polarization discontinuity is expected for In x Ga 1−x N/GaN interfaces on such facets.

Selective area growth has been applied to fabricate a homogeneous array of GaN nanocolumns (NC) with high crystal quality. The structural and optical properties of single NCs have been investigated at the nanometer-scale by transmission electron microscopy (TEM) and highly spatially resolved cathodoluminescence (CL) spectroscopy performed in a scanning transmission electron microscope (STEM) at liquid helium temperatures. TEM cross-section analysis reveals excellent structural properties of the GaN NCs. Sporadically, isolated basal plane stacking faults (BSF) can be found resulting in a remarkably low BSF density in the almost entire NC ensemble. Both, defect-free NCs and NCs with few BSFs have been investigated. The low defect density within the NCs allows the characterization of individual BSFs, which is of high interest for studying their optical properties. Direct nanometer-scale correlation of the CL and STEM data clearly exhibits a spatial correlation of the emission at 360.6 nm (3.438 eV) with the location of basal plane stacking faults of type I1.

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(Ga,Mn)N nanowires were grown by plasma-assisted molecular beam epitaxy on p-type Si(111) substrates. Chemical composition and elemental distribution of single nanowires were analyzed by energy dispersive X-ray spectroscopy revealing an inhomogeneous Mn distribution decreasing from the surface of the nanowires toward the inner core region. The average Mn concentration within the nanowires is found to be below 1%. High-resolution transmission electron microscopy shows the presence of planar defects perpendicular to the growth direction in undoped and Mn-doped GaN nanowires. The density of planar defects dramatically increases under Mn supply.

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An inadvertent error has occurred in the derivation of the theoretical ratio of mand a-plane segment lengths for the GaN equilibrium crystal shape using the Wulff-plot in projection along 0001 as shown in figure 7(b) of our paper (2013 New J. Phys. 15 053045). A value of s = 2.4 was reported, however, the correct value is s = 1.8. Within the accuracy of the measurement, the experimentally derived value of 2.2(4) is in agreement with this corrected value.

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Gallium nitride (GaN) is a binary compound semiconductor which belongs to the group III nitrides (III−N). GaN crystallizes typically in the wurtzite structure and has a direct band gap of 3.4 eV. Other members of the III nitrides are indium nitride (InN) and aluminum nitride (AlN), which likewise are of wurtzite crystal phase. The direct band gaps are 0.7 and 6.2 eV, respectively. The GaN-based ternary alloys In Ga 1− N and Al Ga 1− N theoretically allow to tailor the fundamental band gap from the near infrared (InN) to the far ultraviolet (AlN) parts of the electromagnetic spectrum. No other materials system offers this range of direct band gaps [1] . In fact, GaN-based optoelectronic devices are firmly established in everyday life: Solid-state lighting for illumination applications such as full color displays, automotive headlights and ambient lighting [2] utilize GaN-based light emitting diodes (LEDs). High definition optical data storage devices such as Blu-ray players which operate at a wavelength of 405 nm are based on InGaN laser diodes (LDs).The outstanding properties of the III nitrides in general [1,3] , the possibility to continuously tune the band gap, and especially the high melting temperature and the wide band gap of GaN and AlN, allow to envision a variety of GaN-based (high power) optoelectronic applications. These comprise for example photovoltaics, full visible spectrum LEDs, blue and green LDs for projectors (InGaN), and ultraviolet LDs for photolithography, chemical analysis, and medical, as well as environmental applications (AlGaN) [4,5] .Despite the overwhelming application versatility various problems have to be encountered and overcome to pave the way towards this bright future. One of them is related to the growth direction: The III nitrides are subject to polarization effects which cause internal electric fields. In conventional III−N devices, the growth surface is the polar -plane which is described by the Miller-Bravais indices 0001 . The growth direction perpendicular to this plane is 0001 . For this specific geometry, the built-in electric fields are aligned along the growth direction of the light emitting region, which is detrimental to the performance of these devices. A possibility to circumvent or at least reduce these fields is the growth on nonpolar or semipolar surfaces. The former 1100 -and 1120 -surfaces are perpendicular to the -plane. The latter are identified by { } with nonzero , , indices and 10 :