This dissertation investigates the properties of gallium nitride (GaN) crystals through doping and addresses challenges in the hydride vapour phase epitaxy (HVPE) growth process. The first chapter provides an introduction to GaN single crystal growth history, while the second chapter covers current growth techniques and their impact on GaN properties. It delves into HVPE as a vapour phase epitaxy method, emphasizing the vertical reactor's capabilities for doping. The third chapter focuses on point defects in GaN, particularly extrinsic defects for achieving p-type, n-type, or semi-insulating behavior, reviewing various dopants and discussing point defect diffusion. Chapter four explores the in-situ introduction of iron, manganese, and carbon during crystal growth to counter unintentional doping (UID) and achieve true semi-insulating properties, with a focus on characterizing the pyroelectric coefficient, essential for the Sharp-Garn measurement method. The fifth chapter addresses tensile stress creation from in-situ silicon doping, monitoring strain using Raman spectroscopy, and developing a process to mitigate tensile strain. The sixth chapter presents a new solid-state doping line for delivering doping precursors, focusing on germanium doping's homogeneity compared to silicon and vapour phase methods. The chapter discusses the advantages and disadvantages of these approaches in relation to the growth parameters of HVPE GaN.
