Properties of Optical Resonant Modes in III-NitrideSemiconductor Micro-Cone Cavities

Abstract

Arrays of III-nitride semiconductormicro-cone cavities with a base diameter of 3.3 µm were fabricated byion beam etching. The micro-cones consisted of 58 nm thick multiplequantum wells of In0.22Ga0.78N/In0.06Ga0.94N as wellas a 1.5 µm thick epilayer of GaN. Optical resonant modes from asingle micro-cone could be clearly observed in the photoluminescencespectra at temperatures up to 200 K under a pumping power density twoorders of magnitude lower than that for the III-nitride semiconductormicro-disk or micro-ring cavity. Using a novel optical ray tracing method,we have figured out four main types of optical resonant cavities insidethe three-dimensional micro-cone, including two Fabry-Pérot (F-P)mode types as well as two Whispering Gallery mode types. The threecorresponding mode spacings among the four agree perfectly with theexperimental results. The advantages of this new class of micro-cavityover the other micro-cavities are discussed. These findings are expectedto have an impact on the design of the ultraviolet/blue micro-cavity laserdiodes.