On current injection into single quantum dots through oxide-confined pn-diodes

Current injection into single quantum dots embedded in vertical pn-diodes featuring oxide apertures is essential to the technological realization of single-photon sources. This requires efficient electrical pumping of sub-micron sized regions under pulsed excitation to achieve control of the carrier population of the desired quantum dots. We show experimental and theoretical evidence for a rapid lateral spreading of the carriers after passing the oxide aperture in the conventional p-i-n-design in the low-injection regime suitable for single-photon emitters. By an alternative design employing p-doping up to the oxide aperture the current spreading can be suppressed resulting in an enhanced current confinement and increased injection efficiencies.