Microelectrical characterisation of diamond films: an attempt to understand the structural influence on electrical transport phenomena

The properties of microelectrical conduction in microwave plasma assisted chemical vapour deposition (MPCVD) diamond films were investigated using an atomic force microscopy probe, giving a morphological map of the electrical conduction with a spatial resolution better than 500 nm. Also, a cathodoluminescence map with a spatial resolution of about 1 mu m was obtained, giving the possibility of correlating the defects involved in the different carrier transport phenomena. Using micro-Raman analysis several bands could be identified. It is found that the defects responsible for the cathodoluminescence (CL) blue band are responsible for the major part of the electrical conduction in diamond films, while the defects localised in < 111 > surfaces, responsible for the green CL emission, could be involved in a less conductive process. (C) 2000 Elsevier Science S.A. All rights reserved.

Self-healing thermal annealing: surface morphological restructuring control of GaN nanorods

With advances in nanolithography and dry etching, top-down methods of nanostructuring have become a widely used tool for improving the efficiency of optoelectronics. These nano dimensions can offer various benefits to the device performance in terms of light extraction and efficiency, but often at the expense of emission color quality. Broadening of the target emission peak and unwanted yellow luminescence are characteristic defect-related effects due to the ion beam etching damage, particularly for III–N based materials. In this article we focus on GaN based nanorods, showing that through thermal annealing the surface roughness and deformities of the crystal structure can be “self-healed”. Correlative electron microscopy and atomic force microscopy show the change from spherical nanorods to faceted hexagonal structures, revealing the temperature-dependent surface morphology faceting evolution. The faceted nanorods were shown to be strain- and defect-free by cathodoluminescence hyperspectral imaging, micro-Raman, and transmission electron microscopy (TEM). In-situ TEM thermal annealing experiments allowed for real time observation of dislocation movements and surface restructuring observed in ex-situ annealing TEM sampling. This thermal annealing investigation gives new insight into the redistribution path of GaN material and dislocation movement post growth, allowing for improved understanding and in turn advances in optoelectronic device processing of compound semiconductors.