We have systematically investigated the doping of (1122) with Si and Mg by metal-organic vapour phase epitaxy for light emitting diodes (LEDs). By Si doping of GaN we reached electron concentrations close to 10 20 cm −3 , but the topography degrades above mid 10 19 cm −3. By Mg doping we reached hole concentrations close to 5×10 17 cm −3 , using Mg partial pressures about 3× higher than those for (0001). Exceeding the maximum Mg partial pressure led to a quick degradation of the sample. Low resistivities as well as high hole concentrations required a growth temperature of 900 • C or higher. At optimised conditions the electrical properties as well as the photoluminescence of (1122) p-GaN were similar to (0001) p-GaN. The best ohmic p-contacts were achieved by NiAg metallisation. A single quantum well LED emitting at 465 nm was realised on (0001) and (1122). Droop (sub-linear increase of the light output power) occurred at much higher current densities on (1122). However, the light output of the (0001) LED was higher than that of (1122) until deep in the droop regime. Our LEDs as well as those in the literature indicate a reduction in efficiency from (0001) over semi-polar to non-polar orientations. We propose that reduced fields open a loss channel for carriers.

Extremely weak surface emission from (0001) c -plane AlGaN multiple quantum well structure in deep-ultraviolet spectral region Valence-band splitting and band-gap reduction in ordered GaInAs/InPThe valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k Á p theory yields a critical relative aluminum concentration x c ¼ ð0:0960:05Þ for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with C 9 symmetry of b C 9 ¼ 0:85eV, and propose a possible bowing for the crystal field energy of b cf ¼ À0:12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of Al x Ga 1Àx N=Al y Ga 1Ày N quantum well structures is discussed for different compositions. V C 2014 AIP Publishing LLC. [http://dx.

Polar and semipolar LED structures with InGaN quantum wells (QWs) were investigated in a scanning electron microscope (SEM) using simultaneously electron beam induced current (EBIC) and cathodoluminescence (CL). EBIC yields important information about depletion region, leakages, and the overall functionality of the pn‐junction and allows to determine the diffusion length of the generated minority carriers on both sides of the pn‐junction. Spectrally and spatially resolved CL measurements yield both, information about the QW quality and about centers of non‐radiative recombination. EBIC measurements were carried out in top‐view and in cross‐section between 26thinmathspacenormalK and room temperature. The diffusion lengths measured for polar and semipolar structures prove the better crystal quality of the polar structures in terms of the higher carrier diffusion length and its increase for lower temperatures, as expected. On the semipolar structures, top‐view EBIC measurements detect specific areas, where the pn‐junction seems to be disturbed. The comparison of EBIC and CL measurements shows interesting correlations of the EBIC signal and the emission wavelengths of the quantum wells.

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