Emission from quantum-dot high- microcavities: transition from spontaneous emission to lasing and the effects of superradiant emitter coupling

Measured and calculated results are presented on the emission properties of a new class of emitters operating in the cavity quantum electrodynamics regime. The structures are based on high-finesse GaAs/AlAs micropillar cavities, each with an active medium consisting of a layer of InGaAs quantum dots and distinguishing feature of having substantial fraction of spontaneous emission channeled into one cavity mode (high-beta factor). This paper shows that the usual criterion for lasing with a conventional (low-beta factor) cavity, a sharp nonlinearity in an input-output curve accompanied by noticeable linewidth narrowing, has to be reinforced by the equal-time second-order photon autocorrelation function for confirming lasing. It will also show that the equal-time second-order photon autocorrelation function is useful for recognizing superradiance, a manifestation of the correlations possible in high- microcavities operating with quantum dots. In terms of consolidating the collected data and identifying the physics underlying laser action, both theory and experiment suggest a sole dependence on intracavity photon number. Evidence for this comes from all our measured and calculated data on emission coherence and fluctuation, for devices ranging from LEDs and cavity-enhanced LEDs to lasers, lying on the same two curves: one for linewidth narrowing versus intracavity photon number and the other for g(2)(0) versus intracavity photon number.