Semiconductor microcavities are nanostructures that consist of a planar Fabry-Perot cavity with one or more embedded quantum structures (wells, wires, dots etc), sandwiched between two Bragg mirrors. Coupling between the exciton resonance and the cavity mode may lead to either crossing or anticrossing of the real parts of the eigenfrequencies of the structure modes (called exciton – polariton modes). Excitons-polaritons are half light, half matter quasi particles, combining the properties of excitons and photons, They can be interpreted as virtual exciton-photon pairs, whose propagation in the crystal is just a result of multiple virtual absorption and emission processes of photons by the excitons. A laser excites the semiconductor sample, generating coherent electron-hole pairs, which start interacting with one another. As a result, they lose their coherence and are redistributed in reciprocal space. These ‘hot’ carriers exchange their kinetic energy with the lattice, mostly with optical phonons. During this process, depending on their density and the lattice temperature, carriers may form excitons and populate the exciton dispersion. Then, they relax along the dispersion curve by interacting with acoustic phonons. Carriers which reach the central part of the reciprocal space can emit light, but their relaxation towards that part of the dispersion is hindered. The wavevector conservation selection rule is responsible for the inefficient polariton – phonon or polariton – polariton scattering, that doesn’t allow polaritons to relax rapidly toward the lower energy states.
Micropillars One efficient way of confining polaritons along all spatial directions can be by laterally patterning a planar microcavity in the shape of micropillars photons are confined vertically by the Bragg mirrors and laterally by the index of refraction contrast between the air and the semiconductor. As a result, micropillars exhibit discrete 0D photon modes In the strong coupling regime, polaritons come from the mixing between each of these 0D photon modes and the QW excitons.
Relevant recent publications:
"Longitudinal optical phonon assisted polariton laser"
M. Maragkou, A. J. D. Grundy, T. Ostatnický and P. G. Lagoudakis
Applied Physics Letters
"Spontaneous non-ground state polariton condensation in pillar microcavities"
M. Maragkou, A. J. D. Grundy, E. Wertz, A. Lemaitre, I. Sagnes, P. Senellart, J. Bloch and P.G. Lagoudakis
Physical Review B 81, 081307 (R) (2010) Rapid Comm.
"Ground state polariton condensation in planar GaAs microcavities"
M. Maragkou, A. J. D. Grundy and P. G Lagoudakis
arXiv:0907.3657 [cond-mat.other] (2009)
“Room temperature polariton lasing in semiconductor microcavities”
S. Christopoulos, G. Baldassarri, A. J. Grundy, P.G. Lagoudakis, A.V. Kavokin, J.J. Baumberg, G. Christmann, R. Butte, E. Feltin, J.-F. Carlin, and N. Grandjean
Phys. Rev. Lett. 98, 126405 (2007)