Materials characterization and transmission analysis in erbium-doped gallium nitride microresonator structures

Abstract

GaN:Er is an attractive material for room temperature 1.54 pm luminescence enhancement devices for use in telecommunications because it does not experience thermal quenching at room temperature like Si:Er and can be electronically pumped. GaN:Er layers grown by molecular beam epitaxy (MBE) on single crystal substrates have shown excellent room temperature 1.54 [mu]m luminescence, but to integrate GaN:Er into microresonator devices it is necessary to grow a good quality GaN:Er film on an amorphous substrate. This thesis examines the optical properties and morphology of GaN:Er layers grown on Si₃N₄ and SiO₂ substrates, and evaluates two microresonator devices with incorporated GaN:Er layers. GaN:Er layers grown by MBE on SiO₂ and Si₃N₄ substrates were shown to give room temperature luminescence comparable to that of GaN:Er grown on (11 1)Si. GaN:Er layers grown on a buffered oxide etched Si₃N₄ substrate showed the best luminescence. The ability to grow good quality layers on amorphous substrates allows GaN:Er to be used in waveguide devices, the first of which studied was the microring resonator. Microring resonators were made by depositing a blanket GaN:Er layer on patterned Si₃N₄ microring structures. These structures were damaged, and transmission measurements were not possible. When looking at surface roughness measurements it appears that channel waveguide structures are unsuitable for GaN:Er grown on amorphous substrates, and so a ridge waveguide structure is proposed to lower this surface roughness scattering loss. A microcavity with a GaN:Er defect layer and a-Si/a-SiO₂ stacks was fabricated and tested for luminescence enhancement. The refractive index of GaN:Er was determined by reflectance measurements to be 2.1. The layer was not of uniform thickness which led to a broad resonance peak, but a distortion of the spectrum including a lower luminescence at the 1517 nm peak and a higher luminescence at the 1557 nm peak were observed, which suggests enhancement by the microcavity.