Here, we emphasize the importance of a bottom reflector for achieving unidirectional far-field emission. As a
result, over 80% of photons generated inside the cavity can be collected within a divergence angle of ±30° from
the top. We also discuss interesting analogy in which the nanocavity-bottom reflector coupled system is treated
as a point-like emitter in front of a mirror. Based on such a view point, the observed directivity is explained
by using a comprehensive interference model. Finally, we propose a very practical form of an efficient photonic
crystal nanolaser bonded on a flat metal surface, which may enable current injection and room-temperature
continuous-wave operation.
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