Wide Band Gap SemiconductorOptical Waveguide

Abstract

This dissertation involves the design, fabrication and characterization of wide band gap semiconductor optical waveguide devices. Prism coupling was used as the primary characterization method to obtain design parameters of the refractive index and propagation loss of the wide band gap semiconductor materials such as c-plane, a-plane GaN and ZnO grown on c-plane, r-plane sapphire. AlxGa1-xN alloys and ZnO co-doped with nitrogen, tellurium and chromium diffused sapphire waveguides were also investigated. The simulation and layout of optical waveguide devices, including 1x2 GaN splitters, Mach-Zehnder interferometers and asymmetric twin waveguide devices, were performed using a commercial software package using the beam propagation method. As-grown GaN materials were characterized by using cathodoluminescence, optical transmission measurement, atomic force microscopy and prism coupling. GaN waveguides, 1x2 splitters and Mach-Zehnder interferometers were fabricated and tested at visible wavelengths using HeNe and a tunable Argon laser. The end faces of the waveguide chips were polished by using the sample preparation techniques used in transmission electron microscopy. The morphology of the rib waveguides were characterized by using atomic force microscopy and scanning electron microscopy. A novel light coupling system suitable for high numerical aperture and small dimensional waveguides was designed using the lensed-fiber and a ball lens combination and used to couple light into the waveguide structures.