We investigate the 3.32 eV defect-related emission band in GaN correlating transmission electron microscopy and spatially and spectrally resolved cathodoluminescence at low temperature. The band is unambiguously associated with basal plane stacking faults of type I 2 , which are a common defect type in semi-and nonpolar GaN grown on foreign substrates. We ascribe the luminescence to free-to-bound transitions. The suggested intrinsic acceptors involved have an ionization energy of ≈0.17 eV, and are located at the I 2 -type basal plane stacking faults.
We report about defect-related emission bands in GaN. We establish a direct correlation between results from spatially and spectrally resolved cathodoluminescence bands at 3. 32, 3.23, 3.20, 3.16, and 3.07 eV with findings obtained by transmission electron microscopy. The band around 3.32 eV was unambiguously assigned to I 2 basal plane stacking faults (BSFs). The bands at 3.23, 3.20, 3.16, and 3.07 eV were detected in sample regions, where BSFs exist, but were not assigned to specific defect types, except for the 3.07 eV line which is a phonon replica of the transition at 3.16 eV.
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.
Three-dimensional reciprocal space mapping of semipolar (11{\overline 2}2) GaN grown on stripe-patternedr-plane (1{\overline 1}02) sapphire substrates is found to be a powerful and crucial method for the analysis of diffuse scattering originating from stacking faults that are diffracting in a noncoplanar geometry. Additionally, by measuring three-dimensional reciprocal space maps (3D-RSMs) of several reflections, the transmission electron microscopy visibility criteria could be confirmed. Furthermore, similar to cathodoluminescence, the 3D-RSM method could be used in future as a reliable tool to distinguish clearly between the diffuse scattering signals coming from prismatic and from basal plane stacking faults and from partial dislocations in semipolar (11{\overline 2}2) GaN. The fitting of the diffuse scattering intensity profile along the stacking fault streaks with a simulation based on the Monte Carlo approach has delivered an accurate determination of the basal plane stacking fault density. A reduction of the stacking fault density due to the intercalation of an SiN interlayer in the GaN layer deposited on the sidewall of the pre-patterned sapphire substrate has led to an improvement of the optoelectronic properties, influenced by the crystal quality, as has been demonstrated by a locally resolved cathodoluminescence investigation.
Ga x In 1−x N quantum wells grown by metal organic vapor phase epitaxy on a plane GaN grown on r plane sapphire substrate typically show relatively large surface pits. We show by correlation of low temperature photoluminescence, cathodoluminescence, scanning and transmission electron microscopy that the different semipolar side facets of these pits dominate the overall luminescence signal of such layers.
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