Electrically injected GaN-based microdisk towards an efficient whispering gallery mode laser

III-nitrides based microdisks with the mushroom-type shape are key components for integrated nanophotonic circuits. The air gap undercut in the mushroom-type microdisk is essential for maintaining vertical optical confinement, but this structure is still facing the difficulty of electrical injection. In this work, we demonstrate an electrically injected GaN-based microdisk of such structure. The device is featured with a copper substrate and copper supporting pedestal, through which current can be efficiently injected into the microdisk with low leakage current (less than 10 nA). Bright emission at ∼420 nm was demonstrated from the microdisk under current injection. The copper substrate and supporting pedestal can also extract thermal energy out of the microdisk effectively, and the structure in this work shows a low thermal resistance of ∼788.86 K/W. Low threshold lasing action at ∼405 nm was realized under the optically pumped condition and the threshold energy is ∼35 nJ/pulse. Clear whispering gallery modes were observed and the Q factor is as high as 4504, indicating the high quality of the microdisk cavity. This work is the first step towards low threshold efficient electrically injected microdisk laser with a mushroom-type shape.