Cascaded exciton emission of an individual strain-induced quantum dot

Single strain-induced quantum dots are isolated for optical experiments by selective removal of the inducing InP islands from the sample surface. Unpolarized emission of single, bi- and triexciton transitions are identified by power-dependent photoluminescence spectroscopy. Employing time-resolved experiments performed at different excitation powers we find a pronounced shift of the rise and decay times of these different transitions as expected from cascaded emission. Good agreement is found for a rate equation model for a three step cascade

Self-organized InP islands on (100) GaAs by metalorganic vapor phase epitaxy

The effect of growth temperature, deposition rate, and substrate misorientation angle on size, density, and uniformity of InP islands grown on (100) GaAs by metalorganic vapor phase epitaxy is investigated. The density of InP islands is observed to remain constant as a function of growth temperature in the temperature range of 620–680 °C. Below 620 °C the island density increases with decreasing temperature. Above 605 °C a subset of islands having a uniform size is observed. The degree of uniformity depends largely on the deposition rate and the size of the uniform islands on the growth temperature.Peer reviewe

Self-assembled GaIn(N)As quantum dots: Enhanced luminescence at 1.3 µm

Self-assembled GaIn(N)As quantum dots are fabricated on GaAs by atmospheric pressuremetalorganic vapor-phase epitaxy using dimethylhydrazine (DMHy) precursor as a nitrogen source. The incorporation of nitrogen into the islands is observed to be negligible. However, the areal density of the islands is increased by up to one order of magnitude compared to that of the respective GaInAs islands. The GaIn(N)As island size can also be controlled by varying the DMHy flow. An enhancement of the room-temperature luminescence at 1.3 μm is observed in the GaIn(N)As samples grown with DMHy.Peer reviewe

Temperature dependence of carrier relaxation in strain-induced quantum dots

We report experimental observation and theoretical interpretation of temperature-dependent, time-resolved luminescence from strain-induced quantum dots. The experimental results are well described by a master equation model for the electrons. The intraband relaxation in the conduction band and the radiative recombination rate are governed by the hole populations resulting in prominent temperature dependence of the relaxation process. Even when only a few electrons and holes are confined in a single quantum dot the Auger-like process provides a rapid intraband relaxation channel for electrons that can replace the phonon scattering as the dominant relaxation mechanism.Peer reviewe

Experimental investigation towards a periodically pumped single-photon source

Experiments towards a periodically pumped single-photon source are presented. The lateral piezoelectric field of a surface acoustic wave dissociates laser-generated two-dimensional excitons into electrons and holes. These carriers are separated by the wave potential and are transported over macroscopic length scales without recombining. When reaching a stress-induced quantum dot in the quantum well they periodically populate the zero-dimensional states and recombine, emitting single photons periodically in time according to the surface acoustic-wave frequency. We have successfully reduced the number of pumped quantum dots down to 100 and have detected a strong blinking photoluminescence signal. By further reducing the number of quantum dots down to 1 a periodically pumped single photon source could be realized.Peer reviewe

Observation of defect complexes containing Ga vacancies in GaAsN

Positron annihilation spectroscopy was used to study GaAsN/GaAs epilayers. GaAsN layers were found to contain Ga vacancies in defect complexes. The density of the vacancy complexes increases rapidly to the order of 1018 cm−3 with increasing N composition and decreases after annealing at 700 °C. The anticorrelation of the vacancy concentration and the integrated photoluminescence intensity suggests that the Ga vacancy complexes act as nonradiative recombination centers.Peer reviewe

Tensile-strained GaAsN quantum dots on InP

Self-assembled quantum dots are typically fabricated from compressive-strained material systems, e.g., InAs on GaAs. In this letter, self-assembled quantum dots from tensile-strained GaAsN on InP are demonstrated. GaAsN on InP has type-I band alignment. Stranski-Krastanov growth mode is not observed, but in situannealing of the uncapped samples results in the formation of islands. Photoluminescence spectra from the buried GaAsN show separate peaks due to a wetting layer and islands around the energies of 1.3 and 1.1eV, respectively.Peer reviewe

Selective growth of InGaAs on nanoscale InP islands

The formation of an InGaAs quantum well on nanoscale InP islands by selective growth using metalorganic vapor phase epitaxy is demonstrated. The structures show intense low‐temperature photoluminescence at 1.35 eV. The blueshift of the emission peak by increasing the excitation intensity suggests that the carriers are three‐dimensionally confined. The insertion of quantum well into the islands allows a better control of the properties of structuresfabricated by the self‐organizing growth, a novel technique to realize nanoscale structures without using any lithographical process steps.Peer reviewe

Zeeman Effect in Parabolic Quantum Dots

An unprecedentedly well resolved Zeeman effect has been observed when confined carriers moving along a closed mesoscopic path experience an external magnetic field orthogonal to the orbit plane. Large Zeeman splitting of excited higher angular momentum states is observed in the magnetoluminescence spectrum of quantum dots induced by self-organized InP islands on InGaAs/GaAs. The measured effect is quantitatively reproduced by calculations including the vertical quantum well confinement and strain induced, nearly parabolic, lateral confinement, together with the magnetic interaction.Peer reviewe