(a) The core of a cutoff mode pillar device with a horn antenna structure at the base of the pillar. The horn can radically change the output radiation pattern. (b) Scanning electron micrograph (SEM) of a semiconductor core of a pillar device, before encapsulation in dielectric and metal. The scale bar is 100 nm. The InGaAs region in the center can be seen, and has a slight bulge to enhance confinement. The base of the pillar flares out as often happens in reactive ion etch processes. Furthermore, the process parameters can be adjusted during the etch process to increase the sidewall slope and create horn-like structures at the pillar base.
