Study of the Physical Properties of AlGaN and BGaN Thin Films

Abstract

Group III nitrides, such as GaN, AlN, and InN, and their related alloys have been successfully commercialised as materials for microelectronic and optoelectronic devices. Recently, a new class of alloys has been proposed based on the introduction of boron into ‘classical’ group III nitrides (AlInGa)N to extend the possibilities of bandgap engineering in device structures. The bandgap energies, lattice parameters, and refractive indices are important guidelines for materials engineering. Boron alloyed nitrides are remarkable materials that have not yet been fully explored owing to material growth limitations and issues with phase control. It should also be emphasized that AlGaN alloys have the advantage of good chemical stability at high temperatures. However, the growth of this type of membrane remains difficult owing to the lack of substrates. In this thesis, the optical, structural, and morphological properties of AlGaN and BGaN epitaxial thin films were investigated using a variety of characterisation techniques, including spectroscopic ellipsometry (SE), photoluminescence (PL), scanning electron microscopy (SEM), and reflectometry measurements. The effects of adding aluminum (Al) and boron (B) are discussed by comparison with the properties of a reference GaN film.