Optically pumped multi-mode whispering-gallery mode (WGM) lasing has been observed in optically free-standing InGaN/GaN quantum well microdisks at room temperature. The ～6.6 μm optically isolated microdisks are patterned by microsphere lithography on GaN thin-films prepared by laser lift-off of the sapphire substrate, enabling superior optical confinement. The modes are determined to be of second order according to simulations. The lasing threshold is found to be ～9.06 mJ/cm~2, with a quality factor Q of ～770 evaluated from the dominant mode at λ = 430.2 nm, and a free space range (FSR) of 3.17 to 2.16 nm, which is mode-dependent.
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