Stress Related Effects Of GaN Based Semiconductor Heterostructures

GaN-based semiconductor has been one of the most important and potential optoelectronic materials,the heterostructure of which plays the dominant role in the fabrication of new functional devices. However, several critical problems that have significantly restricted the further development of its advanced applications are principally related to its stress field. The research in this thesis aimed to provide a thorough insight into the stress-related effects in the GaN-based heterostructures, especially at the nano-scale heterointerface, through both experimental and theoretical studies.The epitaxial heterostructures, such as epitaxial-lateral-overgrowth (ELO) GaN and AlGaN/GaN, were prepared by using metal-organic chemical vapor deposition. Advanced characterization techniques, including scanning electron microscopy, Auger electron spectroscopy, cathodoluminescence, etc., were employed for analyzing the chemical and physical properties of the heterostructures. Concepts of"Electron cipher"and"Auger general shift"were proposed for the first time, which led to the establishment of nano-scale measurements for local stress field, electric field, and charges. Upon the framework of the first-principles calculation methods, the construction techniques for modeling heterstructure systems and imposing stress fields were developed. Based on above techniques, following issues have been studied and important approaches were obtained:1. The stress field and optical properties of ELO-GaN were investigated. The stress distribution on the cross section suggests a mechanism of the release of misfit in-plane stress and the critical release region was determined. The bending of threading dislocations (TDs), the climb movement of dislocation loops, and the jog of stacking faults have been observed and analyzed and the results proved the existence of a longitudinal stress field in the lateral region. Such stress field results in the enhancement effect of band-edge emission efficiency and consequently, improves the ultraviolet luminescence intensity. On the other hand, the horizontal dislocation array introduces the fragmentation effect into the c-axial polarization field, which also effectively improves the recombination rate of electron-holes.