Enhancing Optical Confinement of InGaN Thin-Film Microdisk Lasers with Hybrid Omnidirectional Reflectors

Abstract

<p>The conventional GaN microdisk laser adopts an undercut structure for the optical confinement, which provides poor overlap between the whispering gallery modes and the multiquantum well gain region. The thin-film microdisk structure was proposed to overcome this shortcoming, but the absorptive nature of the metallic bonding layer with mirror compromises optical confinement. In this work, an SiO₂/TiO₂ distributed Bragg reflector is integrated with the metallic mirror to form an omnidirectional reflector that provides high optical reflectance across a wide range of incidence angles to promote optical confinement in the microdisk. Optical-pumped lasing with an average lasing threshold power density of 46.5 W/cm² and Q factors of 18200 (near threshold) is achieved. The narrowest lasing line width of ∼0.02 nm is obtained at the average excitation power density of 48.02 W/cm², representing a major advancement in the GaN microdisk laser technology.<br></p>