Analysis of the gallium nitride-sapphire thick films, processed by iodine vapor phase growth by transmission electron microscopy and atomic force microscopy

Semiconductor nitrides such as gallium nitride (GaN), aluminum nitride (AlN) and indium nitride (InN) are very promising materials for their potential use in optoelectronic devices and high power/temperature electronic devices. Many different methods have been used for the processing of the thick epitaxial layer GaN. Iodine Vapor Phase Growth (IVPG) is a new technique that promises a better product. This work is a first of its kind as a systematic study of the GaN thick films produced by IVPG process. The key points of concentration in this work are buffer layer, polarity and dislocation density. It was seen that rougher buffer layers produce better epilayers. An in-depth study of the buffer layer on a-plane and c-plane sapphire substrate is also presented. Polarity measurements have been carried out with Atomic Force Microscopy. The dependence of the polarity and dislocation density on the processing conditions has been shown in this study. For the first time dislocation density has been measured as a function of distance from the substrate, clearly showing its variation. It has been shown that the dislocation density data obtained from AFM can be correlated with the data obtained from TEM. New techniques have been suggested and tried out for the measurement of polarity. The ability of Electrostatic Force Microscopy as a potential tool in analyzing the uniformity of the polarity of the samples has also been demonstrated here. The results obtained here can be used to construct better operating conditions.