Correlation of Surface Potential, Free Carrier Concentration and Light Emission in ELO GaN Growth Domains

We have carried out spatially resolved micro-Raman spectroscopy, cathodoluminescence micro-scopy and scanning capacitance microscopy in order to obtain a comprehensive understanding about the properties of different domains formed in epitaxial laterally-overgrown GaN. For this purpose a spherical pit was fabricated into the sample by mechanical grinding and polishing, penetrating through to the buffer layer at its center. We found areas showing sharp excitonic luminescence corresponding to local free-carrier concentrations n below 1017 cm – 3 as well as domains exhibiting broad luminescence originating from recombination of a doping plasma with n reaching 1019 cm – 3. Simultaneously, we observed in the scanning microscopy investigations a substructure which could be explained by the existence of internal space charge regions. Introduction The technique of epitaxial lateral overgrowth (ELO) has been proven successful in reducing the dislocation density in GaN by a few orders of magnitude [1, 2]. Despite of this technical progress there are still open questions to be answered leading to a better understanding of the structural properties of ELO GaN. While cathodoluminescence microscopy (CL) and micro-Raman spectroscopy are known to b