This work investigates dislocation etch pits in epitaxial lateral overgrowth (ELO) GaN by wet chemical etching. A mixture of H2SO4 and H3PO4 was used as a dislocation etchant, and SEM and AFM were employed to observe the surface topography. For the as-grown sample, SEM images present the flat, smooth surface without any pits or hillocks. After the chemical etching, hexagonal shaped etch pits were observed at the edge of ELO GaN. AFM observation of etched ELO GaN displayed high densities of etch pits clustered in the “window” region and the coalescent line of two growing fronts. In contrast, the overgrowth region was nearly free of etch pits. Moreover, we observed that different sizes of etch pits dominated in “window” region and coalescent region. This implied different types dislocations dominated in these regions.
The optical properties of InAs/GaAs Quantum Dots have been studied by comparing the photoreflectance and photoluminescence spectra at different temperatures. The photoreflectance relative spectral intensity between the contributions from InAs wetting layer and the GaAs increases with the decreasing of temperature. The photoluminescence spectral profiles consist of contributions from the equal spacing energy levels of the InAs quantum dots. Since the quantum dot transitions were observed in the photoluminescence spectra and the wetting layer transitions were observed in the photoreflectance spectra, we propose that the Fermi level of the system is located between energy level of the wetting layer and the populated energy level of the quantum dots.
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