Electrically Driven Quantum Dot Micropillar Light Sources

We report on light sources based on electrically pumped quantum dot (QD) micropillar cavities. The low-mode-volume high-quality microstructures feature pronounced cavity quantum electrodynamics (cQED) effects that are exploited for the realization of efficient single-photon sources and low-threshold microlasers. The compact and electrically driven devices are of special interest for applications in the field of quantum communication. In particular, operated as electrically triggered single-photon sources, the QD micropillars can act as building blocks for quantum key distribution and quantum repeaters. On the other hand, the electrically pumped microlasers with in-plane emission via whispering gallery modes or emission normal to the sample's surface are predestinated for integrated light sources in future photonic networks. The devices are based on doped high-quality factor GaAs/AlAs microcavity structures with InGaAs QDs in the active layer. A lateral injection scheme leaves the upper facet of the micropillars free of any absorbing metal and allows for efficient light output under electrical pumping of low-mode-volume micropillars with diameters between 1 and 20 mu m. Due to cQED effects, triggered single-photon emission with high photon extraction efficiency up to 62% and a low multiphoton emission probability (g((2)) (0) = 0.16) are realized for moderate-quality (Q) factor samples. The efficient coupling of spontaneous emission into the lasing mode in high-Q micropillars results in ultralow laser threshold currents of less than 10 mu A at cryogenic temperatures. Our paper demonstrates the high potential of electrically driven QD micropillars to act as integrated light sources in future communication systems.