Properties of optical resonant modes in III-nitride semiconductor micro-cone cavities

Arrays of III-nitride semiconductor micro-cone cavities with a base diamete r of 3.3 mum were fabricated by ion beam etching. The micro-cones consisted of 58nm thick multiple quantum wells of In0.22Ga0.78N/ln(0.94)Ga(0.94)N as well as a 1.5 mum thick epilayer of GaN. Optical resonant modes from a sin gle micro-cone could be clearly observed in the photoluminescence spectra a t temperatures up to 200K under a pumping power density two orders of magni tude lower than that for the m-nitride semiconductor micro-disk or micro-ri ng cavity. Using a novel optical ray tracing method, we have figured out fo ur main types of optical resonant cavities inside the three-dimensional mic ro-cone, including two Fabry-Perot (F-P) mode types as well as two Whisperi ng Gallery mode types. The three corresponding mode spacings among the four agree perfectly with the experimental results. The advantages of this new class of micro-cavity over the other micro-cavities are discussed. These fi ndings are expected to have an impact on the design of the ultraviolet/blue micro-cavity laser diodes.