Within this work we present optical and structural properties of InP quantum dots embedded in ͑Al x Ga 1−x ͒ 0.51 In 0.49 P barriers. Atomic force microscopy measurements show a mainly bimodal height distribution with aspect ratios ͑ratio of width to height͒ of about 10:1 and quantum dot heights of around 2 nm for the smaller quantum dot class ͑type A͒ and around 4 nm for the larger quantum dot class ͑type B͒. From ensemblephotoluminescence measurements we estimated thermal activation energies of up to 270 meV for the type-A quantum dots, resulting in a 300 times higher luminescence intensity at 200 K in comparison to our InP quantum dots in Ga 0.51 In 0.49 P at the same emission wavelength. Photon statistic measurements clearly display that InP quantum dots in ͑Al 0.20 Ga 0.80 ͒ 0.51 In 0.49 P emit single photons up to 80 K, making them promising candidates for high-temperature single-photon emitters.
The dark exciton state strongly affects the optical and quantum optical properties of flat InP/GaInP quantum dots. The exciton intensity drops sharply compared to the biexciton with rising pulsed laser excitation power while the opposite is true with temperature. Also, the decay rate is faster for the exciton than the biexciton and the dark-to-bright state spin flip is enhanced with temperature. Furthermore, long-lived dark state related memory effects are observed in second-order cross-correlation measurements between the exciton and biexciton and have been simulated using a rate-equation model.
Single pairs of vertically stacked asymmetric pairs of InP quantum dots embedded in GaInP barriers have been investigated as a function of interdot spacer thickness. Time integrated and time-resolved photoluminescence measurements have been performed, with the former showing a change in the intensity ratio between the two dots and the latter an increasing difference in the photoluminescence decay time of the two dots when reducing the spacer thickness. Hence, we suggest transitions from vanishing tunnel coupling to electron tunneling and, finally, to electron and hole tunneling for decreasing barrier widths. The different times are estimated from the measurement data, and the changes are described by a rate equation model. The results clearly show the nonresonant character of the tunneling process as a result of the different ground state energies ͑approximately 40 meV͒ of the unequally sized dots.
We present an electrically pumped single-photon emitter in the visible spectral range, working up to 80 K, realized using a self-assembled single InP quantum dot. We confirm that the electroluminescense is emitted from a single quantum dot by performing second-order autocorrelation measurements and show that the deviation from perfect single-photon emission is entirely related to detector limitations and background signal. Emission from both neutral and charged exciton complexes was observed with their relative intensites depending on the injection current and temperature.
Electrically driven quantum dot single-photon source at 2GHz excitation repetition rate with ultra-low emission time jitter Appl. Phys. Lett. 102, 011126 (2013); 10.1063/1.4774392Triggered single-photon emission in the red spectral range from optically excited InP/(Al,Ga)InP quantum dots embedded in micropillars up to 100 K
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