TWO-DIMENSIONAL WIDE BAND GAP SEMICONDUCTORS FOR DEEP UV PHOTONICS

Abstract

Light emitters and detectors in the deep ultraviolet range (DUV) are of great current interest, with applications in water purification, solar-blind photodetectors and communication, biohazard detection, and phosphor-assisted white light emitters. However, DUV optoelectronics based on solid-state heterostructures suffer from low internal and external quantum efficiencies, due to issues relating to their fundamental material properties. These limitations motivate the exploration of new classes of materials for these applications. The recent emergence of two-dimensional (2D) materials has opened up new possibilities in this area, however 2D materials also bring new experimental challenges: particularly the deposition and characterisation of atomic layers, as well as scientific challenges, especially understanding how interactions between the 2D layer and the substrates and/or the environment may affect the properties of the 2D layer.

In this thesis, the optical properties of promising materials for deep UV photonics are assessed using a combination of techniques, and the mathematical links between the resulting data are demonstrated. The first part of this work discusses the optical and structural properties of gallium nitride and its alloys, which are the foundation of current optoelectronics, and addresses the optical processes of freestanding and supported 2D hexagonal boron nitride (h-BN) as a potential candidate for high-efficiency deep UV optoelectronic devices. The objectives are to (i) confirm the validity of the models on well-known materials, (ii) determine whether h-BN is a good candidate for deep UV optoelectronics and (iii) whether and how interactions between 2D h-BN with substrates must be taken into consideration. The second part discusses the optical properties of barium zirconate titanate with changes in composition and dimensionality. The objectives are (i) to apply models developed for the nitrides to extract the bulk properties of these oxides, and (ii) to determine whether they are good candidates for deep UV optoelectronics in their 2D form.