Approaching the deep green and yellow spectral region in electroluminescence of GaInN/GaN quantum well light emitting diodes (LEDs) requires high alloy fractions of InN which induces a high level of biaxial strain of up to 3%. While in typical sapphire-based epitaxy, among a high density network of threading dislocations (10⁸ - 10⁹ cm^-2), an inclination of such defects is seldom seen, we find those to occur reliably and high density in homoepitaxy on low-dislocation density (~10⁶ cm^-2) c-plane bulk GaN. Their observation revises the long-held interpretation that the smallest available Burgers vector was too large to be likely in this hexagonal crystal structure. We find an inclination angle of 18 - 23° whenever pairs of two dislocations emanate from the GaInN layers and branch off in opposite directions or a 120° pattern. Both dislocations are edge-type and have the Burgers vectors in the growth plane. We don't find any precursor defects suggesting that both Burgers vectors sum up to zero. Comparing various models of the acting forces, we find that the partial strain relaxation induced by the separation of both branches in the pair is the most likely process at work. We find that an open core structure that includes alternate translations of a-lattice vectors can very well describe our observations. This strain relaxation mechanism is thought to play a relevant role in the light output performance of wavelength-stabilized green LEDs.

This work was supported by a DOE/NETL Solid-State Lighting Contract of Directed Research under DE-FC26-06NT42860.

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1. Wavelength-Stable Green Light Emitting Diodes in Non-Polar GaInN/GaN Quantum Well Growth