In recent years, III-Nitride materials including GaN, AlN, InN, ScN, and its ternary alloys have drawn attention for use in various power electronics and optoelectronics technologies. These include power-switching devices, radio frequency devices, light-emitting diodes, laser diodes, solar cells, etc. Investigations for some of the binary and ternary III-nitrides are still in the infancy phase, lacking an understanding of the mechanisms dictating their physical properties. It is important to have a better understanding of the material properties to achieve better quality of the material. The structural property of the material is one of the most important factors for determining the electrical and optical performance and understanding the defect mechanisms is crucial for the advancement of the novel devices. Investigations of the structural properties coupled with other electrical and optical performances in GaN, AlInN, AlGaN, and ScAlN grown via the Metal Modulated Epitaxy (MME) technique, a modern growth technique in the Molecular Beam Epitaxy (MBE) system, are explained in the present dissertation.