Fabrication and Characterization of GaN-Based Superluminescent Diode for Solid-State Lighting and Visible Light Communication

Abstract

To date, group-III-nitride has undergone continuous improvements to provide a broader range of industrial applications, such as solid-state lighting (SSL), visible light communications (VLC), and light projection. Recently, VLC has attained substantial attention in the field of wireless communication because it offers ~ 370 THz of bandwidth of unregulated visible spectrum, which makes it a critical factor in the evolution of the 5G networks and beyond. GaN-based light-emitting diode (LED) and laser diode (LD) have become increasingly appealing in energy-sufficient SSL replacing conventional light sources. However, III- nitride LEDs suffer from efficiency-droop in their external quantum efficiency associated with high current densities, and their modulation bandwidth is limited to 10 ~ 100 MHz. Although LDs have shown gigabit-modulation bandwidth, unfavorable artifacts, such as speckles are observed, which may raise a concern about eye safety. This dissertation is devoted to the fabrication and electrical and optical characterization of a new class of III-nitride light-emitter known as superluminescent diode (SLD). SLD works in an amplified spontaneous emission (ASE) regime, and it combines several advantages from both LD and LED, such as droop-free, speckle-free, low-spatial coherence, broader emission, high-optical power, and directional beam. Here, SLDs were fabricated by a focused ion beam by tilting the front facet of the waveguide to suppress the lasing mode. They showed a high-power of 474 mW on c-plane GaN-substrate with a large spectral bandwidth of 6.5 nm at an optical power of 105 mW. To generate SLD- based white light, a YAG-phosphor-plate was integrated, and a CRI of 85.1 and CCT of 3392 K were measured. For the VLC link, SLD showed record high-data rates of 1.45 Gbps and 3.4 Gbps by OOK and DMT modulation schemes, respectively. Additionally, a widely single- and dual-wavelength tunability were designed using SLD-based external cavity (SLD-EC) configuration for a tunable blue laser source. These results underscore the practicality of c-plane SLDs in realizing high-power, high data rate, speckle-free, and droop-free SSL-VLC apparatus. Additionally, the SLD-EC configuration allows a wide range of applications, including biomedical applications, optical communication, and high-resolution spectroscopy.