Epitaxial GaN films of thickness ∼1 μm have been grown on sapphire(0001) and GaAs(001) substrates using the liquid-target pulsed-laser-deposition technique in a 5 Torr nitrogen atmosphere. Detailed x-ray diffraction and photoluminescence studies were carried out for both types of samples. Significantly enhanced low-temperature photoluminescence emissions at 3.368 eV (I3) and 3.310 eV (I4) were observed for the material deposited on a GaAs(001) substrate at ∼800 °C. We propose a model to explain the emission mechanism for both lines in which the electrons and holes are confined in cubic inclusions within the hexagonal material, analogously to a type-I quantum well.
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