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

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.