Hannu Koskenvaara

Structural and optical properties of GaInNAs/GaAs quantum structures

Structural and optical properties of GaInNAs/GaAs quantum structures grown by metalorganic vapour phase epitaxy (MOVPE) are studied. The growth of arsenide–nitrides by MOVPE is reviewed and compared to the other major growth technique, molecular beam epitaxy. Post-growth thermal annealing and laser irradiation are employed and found to affect GaInNAs quantum wells differently: with laser treatment no undesired blue-shift of the photoluminescence peak is observed. The critical thickness for misfit dislocation formation of GaAsN on GaAs is found to be about twice as large as the theoretical prediction. GaAsN epilayers are also found to contain Ga vacancies in defect complexes. The current status of experimental research on GaInNAs quantum dot structures is reviewed. Self-organized and strain-induced GaInNAs quantum dots are grown and their formation and optical properties are studied. The emission wavelength of InGaAs quantum dots is extended by using InGaAs and GaInNAs barrier layers.

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 situ annealing 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.

Photoluminescence study of strain-induced GaInNAs/GaAs quantum dots

Strain-induced Ga0.8In0.2NyAs1−y quantum dots on GaAs were fabricated by metal organic vapor phase epitaxy. Nitrogen concentration y was varied between 0% and 1.3%. The effect of nitrogen concentration on the optical properties of the quantum dots was investigated by continuous-wave and time-resolved photoluminescence measurements. Carrier localization in the states below the band edge of the nitrogen-containing quantum well has been observed. These states are thought to originate from the variation of the quantum well width or from the fluctuation of the composition. Such variations have been identified in GaInNAs quantum wells on GaAs without stressor islands. The measured energy difference of the quantum well and quantum dot ground-state peak energies increase with increasing temperature.

Effect of surface states on carrier dynamics in InGaAsP/InP stressor quantum dots

The carrier dynamics in strain-induced InGaAsP/InP quantum dots (QDs) is investigated by time-resolved photoluminescence and continuous-wave photoluminescence. The stressor QDs are fabricated by depositing self-assembled InAs islands (or stressor islands) on top of a near-surface InGaAsP/InP quantum well (QW). The temporal behaviour of the QD photoluminescence transients are observed to exhibit a two-phase decay. Rate equation analyses reveal that by increasing the distance of the QW from the surface the surface capture time constant is increased considerably while the capture time constant of an electron from the QW to the QD is decreased.

Highly Tunable Emission from Strain-Induced InGaAsP/InP Quantum Dots

Low-temperature photoluminescence (PL), tunable between 1.3 and 1.7 µm, is obtained from strain-induced quantum dots (SIQDs). The quantum dots are fabricated by growing self-assembled InAs stressor islands on top of a near-surface InGaAs(P)/InP quantum well (QW). The structure is tuned by varying the composition of the QW and its distance from the surface. Time-resolved PL measurements reveal that QD relaxation and recombination time constants (0.55 and 0.50 ns) are virtually independent of the composition of the nearly lattice-matched InGaAsP layer. Also, decreasing the QW distance from the surface is shown to shift the energy states and significantly diminish the PL intensity of the SIQD.

Carrier Dynamics in Strain Induced Quantum Dots Modeled by Rate Equations and Gaussian Excitation Beam Distribution

Strain induced quantum dots are investigated by time resolved and continuous wave photoluminescence spectroscopy. Carrier dynamics is modeled with rate equations taking into account also the Gaussian intensity distribution of the excitation beam. It is shown that the Gaussian distribution has a clear effect on the saturation behaviour of the quantum dot peak intensities. The calculated intensities agree better with the measured luminescence intensities than results from the conventional rate equation approach. [DOI: 10.1143/JJAP.47.5499]