The smaller the size of a light-emitting microcavity, the more important it
becomes to understand the effects of the cavity boundary on the optical mode
profile. Conventional methods of laser physics, such as the paraxial
approximation, become inapplicable in many of the more exotic cavity designs to
be discussed here. Cavities in the shape of microdisks, pillars and rings can
yield low lasing thresholds in a wide variety of gain media: quantum wells,
wires and even dots, as well as quantum cascade superlattices and GaN. An
overview of the experimental and theoretical status is provided, with special
emphasis on the light extraction problem.Comment: PDF generated by pdflate