Semipolar ð1122Þ oriented GaN has been grown on a prestructured r-plane sapphire substrate. By using silicon doped marker layers (MLs) we have been able to monitor the growth evolution of the stripes until coalescence. With that technique we correlated the growth type (direction) with the results of cathodoluminescence (CL) and transmission electron microscopy. Both characterization methods show only a few defects for the major part of the structure and a relatively high defect density for material grown in a-direction at one side of the stripes. It is shown that during coalescence these defects are mainly terminated resulting in a flat, planar ð1122Þ GaN layer with strongly reduced defect density. Additionally, X-ray diffraction (XRD) measurements show the high quality of these layers.

We have studied the growth of GaInN/GaN quantum wells on various polar, nonpolar and semipolar planes. From a detailed x-ray diffraction analysis, we derive the strain state and the composition of the quantum wells. The optical emission energy is obtained from photoluminescence spectra and modelled taking into account the deformation potentials and the Stark shifts. Both x-ray and optical data consistently show that indium incorporation is identical on the polar, nonpolar and semipolar planes within the experimental uncertainty.

We report on the optical properties of m-plane GaInN/GaN quantum wells (QWs). We found that the emission energy of GaInN QWs grown on m-plane SiC is significantly lower than on nonpolar bulk GaN, which we attribute to the high density of stacking faults. Temperature and power dependent photoluminescence reveals that the GaInN QWs on SiC have almost as large internal quantum efficiencies as on bulk GaN despite the much higher defect density. Our results indicate that quantum-wire-like features formed by stacking faults intersecting the quantum wells provide a highly efficient light emission completely dominating the optical properties of the structures. V C 2011 American Institute of Physics. [doi:10.1063/1.3607301] In the past few years, GaN-based light emitting devices grown on non-polar planes have continuously attracted increasing attention due to their promising optical properties. While conventional structures grown on the polar c-plane suffer from the quantum-confined Stark effect (QCSE), 1 GaN layers grown on non-polar surfaces are free from polarization fields in growth direction. 2 The increased transition probability may result in an improved device efficiency leading to increased light output powers and/or reduced threshold current densities. 3 Indeed, the first GaInN based laser diodes with an emission wavelength at 500 nm have been shown by Okamoto et al. on m-plane GaN substrates. 4 However, up to now, non-polar GaN substrates are still barely available, small in size, and also very expensive. As an alternative, several groups have reported heteroepitaxial growth of non-polar GaN layers on foreign substrates (c-LiAlO 2 , SiC, r-plane sapphire). [5][6][7] However, most of these structures were affected by high densities of threading dislocations (TDs) and basal plane stacking faults (BSFs), which are terminated by either prismatic stacking faults (PSFs) or partial dislocations. 8 While TDs are known to act as nonradiative recombination centers, BSFs are optically active since they can be considered as cubic (zincblende) ABC phases in the wurtzite ABAB stacking sequence. Such a structure forms a type-II heterojunction which may capture electrons and holes resulting in optical transitions below the wurtzite GaN bandgap energy. 9-11 More recently, a BSF related emission from aplane GaN/AlGaN quantum well (QW) structures was reported, suggesting the formation of quantum-wire-like states in the regions where BSFs intersect the QWs. 12,13 In this paper, we investigate the optical properties of m-plane GaInN/GaN QW structures grown on silicon carbide (SiC). In particular, we show that stacking faults intersecting the QWs dominate the optical properties of these structures.Our samples were grown on m-plane 6H-SiC, m-plane bulk GaN substrates, and a-plane GaN templates (grown by hydride vapor phase epitaxy) in a low pressure metalorganic vapor phase epitaxy system with a horizontal reactor (Aixtron AIX 200RF). The precursors used were trimethylgallium, triethylgallium, trimethylaluminum, trimethylindium,...

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GaInN/GaN multiple quantum well structures grown on polar and nonpolar surfaces have been compared with respect to the indium incorporation efficiency in the quantum wells (QWs). Under the same growth conditions X-ray diffraction measurements reveal similar growth rates and In concentrations for c-plane, a-plane, and m-plane with In contents up to 40%.These results are in good agreement with optical experiments, in particular for homoepitaxial growth. However, there is strong evidence that the optical properties of the nonpolar heteroepitaxial GaInN QWs are dominated by the high density of stacking faults in those samples.