Ultraviolet nanolaser of inverted hexagonal ZnO pyramid resonating in helical whispering-gallery-like mode.

ZnO nanocavities have advantage to working as optoelectrical nanodevices integrated on chip at high temperature owing to high exciton binding energy. In this work, a single inverted hexagonal ZnO pyramid (HZOP) nanolaser is fabricated successfully by reducing the defect with chemical vapor deposition (CVD). The optical leakage of HZOP is conquered by the inverted configuration to increase the refractive index contrast between ZnO pyramid and surrounding media. Helical whispering-gallery-like mode is proposed to dominate the lasing of HZOP nanolaser. All of the lasing peaks are found to exist at wavelength longer to the fluorescence emission of ZnO, which is ascribed to the large loss represented by the large imaginary part of ZnO refractive index at shorter wavelength. The threshold and linewidth are measured to be 5.27 mJ/cm2 and 0.27 nm, respectively. HZOP nanolaser is a new ultraviolet coherent light source to be integrated on chip at room temperature or higher temperature.