In this article two methods for improvements of (11$ \bar 2 $2) oriented semipolar GaN grown by MOVPE on prestructured sapphire substrates are investigated. The integration of a SiNx interlayer helps to obtain a better crystal quality. Also the overgrowth of the MOVPE samples by HVPE is a way to obtain a smoother GaN surface. A high incorporation of oxygen on (11‐22) oriented GaN compared to (0001) oriented GaN grown by HVPE was observed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We demonstrate the application of low-temperature cathodoluminescence (CL) with high lateral, depth, and spectral resolution to determine both the lateral (i.e., perpendicular to the incident primary electron beam) and axial (i.e., parallel to the electron beam) diffusion length of excitons in semiconductor materials. The lateral diffusion length in GaN is investigated by the decrease of the GaN-related luminescence signal when approaching an interface to Ga(In)N based quantum well stripes. The axial diffusion length in GaN is evaluated from a comparison of the results of depth-resolved CL spectroscopy (DRCLS) measurements with predictions from Monte Carlo simulations on the size and shape of the excitation volume. The lateral diffusion length was found to be (95 ± 40) nm for nominally undoped GaN, and the axial exciton diffusion length was determined to be (150 ± 25) nm. The application of the DRCLS method is also presented on a semipolar (112¯2) sample, resulting in a value of (70 ± 10) nm in p-type GaN.

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The electroluminescence (EL) output power of c‐plane InGaN/GaN‐based light‐emitting diodes (LEDs) is much higher than that of semipolar {10true1‾1} and {11true2‾2} LEDs at the same operation current. In order to elucidate the reasons for this behavior, we have fitted the pulsed EL data by the well‐known ABC model to extract the internal quantum efficiency (IQE) and the carrier injection efficiency (CIE) to clarify which parameter weighs more for the poor EL output power of the semipolar LEDs. The CIE shows large differences, 78%, 4%, and 4% for the c‐plane, {10true1‾1} and {11true2‾2} LEDs, respectively, whereas the IQE values are fairly the same for all three structures. The fit of resonant photoluminescence (PL) data at room temperature confirms the similar IQE values for all three structures. The CIE was increased from 4% to 10% for the planar {11true2‾2} LED with better electrical conductivity of the p‐GaN layer.