Spontaneous emission extraction and Purcell enhancement from thin-film 2-Dphotonic crystals

Electromagnetic band structure can produce either an enhancement or a suppr ession of spontaneous emission from two-dimensional (2-D) photonic crystal thin films. We believe that such effects might be important for light emitt ing diodes. Our experiments were based on thin-film InGaAs/InP 2-D photonic crystals at ambient temperature, but the concepts would apply equally to I nGaN thin films, for example. We show that the magnitude of Purcell enhance ment factor, F-p similar to 2, for spatially extended band modes, is simila r to that for a tiny mode in a three-dimensional (3-D) nanocavity. Nonethel ess, light extraction enhancement that arises from Zone folding or Bragg sc attering of the photonic bands is probably the more important effect, and a n external quantum efficiency > 50% is possible. Angle resolved photolumine scence from inside the photonic crystal gives a direct spectral readout of the internal 2-D photonic band dispersion. The tradeoffs for employing vari ous photonic crystal structures in high efficiency light-emitting diodes ar e analyzed.