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

Comparison of ammonia plasma and AlN passivation by plasma-enhanced atomic layer deposition

Surface passivation of GaAs by ammonia plasma and AlN fabricated by plasma-enhanced atomic layer deposition are compared. It is shown that the deposition temperature can be reduced to 150 °C and effective passivation is still achieved. Samples passivated by AlN fabricated at 150 °C show four times higher photoluminescence intensity and longer time-resolved photoluminescence lifetime than ammonia plasma passivated samples. The passivation effect is shown to last for months. The dependence of charge carrier lifetime and integrated photoluminescence intensity on AlN layer thickness is studied using an exponential model to describe the tunneling probability from the near-surface quantum well to the GaAssurface.Peer reviewe

Catalyst-free growth of In(As)P nanowires on silicon

The catalyst-free metal organic vapor phase epitaxialgrowth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowiregrowth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InPnanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies.Peer reviewe

Enhanced luminescence from catalyst-free grown InP nanowires

The surface effects in the optical properties of catalyst-free grownInPnanowires are investigated. Both as-grown nanowires and nanowires treated with hydrofluoric acid are studied using low- and room-temperature continuous-wave and time-resolved photoluminescence measurements and transmission electron microscopy. It is shown that the room-temperature photoluminescence intensity is increased by two orders of magnitude after the surface treatment, and that there is also a significant increase in the double-exponential photoluminescence decay time.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

In situ determination of nitrogen content in InGaAsN quantum wells

The growth of InGaAsN/GaAs multiple quantum well structures by metal-organic vapor phase epitaxy is monitored by in situ reflectometry. The nitrogen incorporation is found to depend superlinearly on the precursor flow and a threshold value for the flow is observed. By in situmeasurements of the InGaAsN quantum well samples with a fixed indium content, the change in the reflectance during the quantum wellgrowth is found to be linearly dependent on the quantum well nitrogen content. A model to determine the nitrogen content already during the growth is developed. Moreover, the field of application of in situ reflectance monitoring is extended from thick layers to thin layers, including quantum wells.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

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

Neuropsychological intervention of dyslexia has a positive effect on aspects of psychological well-being in young adults - a randomized controlled study

Effectiveness of individual- and group-based neuropsychological intervention on aspects of psychological well-being of dyslexic adults was evaluated. Dyslexic young adults (n = 120) were randomly assigned into individual intervention, group intervention or wait-list control group. Both interventions focussed on cognitive strategy learning, supporting self-esteem, and using psychoeducation. In group format peer support was also utilized. Cognitive and behavioural strategies, mood states, quality of life and self-esteem were assessed via self-report questionnaires at baseline, after the intervention/wait-list control time at 5 months and 10 months. Results indicated that the neuropsychological interventions had a positive effect on self-evaluated cognitive and behavioural strategies, especially in increasing success expectations and to a lesser degree in diminishing task-avoidance and in group intervention in diminishing social pessimism. The interventions also improved cognition-related quality of life and, to a lesser degree, self-esteem. These results indicate that structured neuropsychological interventions can positively affect self-evaluated psychological well-being, especially on cognitive and behavioural strategies. Considering the secondary consequences of dyslexia, support among young adults is often needed beyond the cognitive and reading-based challenges dyslexia poses.Peer reviewe