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Nitrogen migration in ZnO was investigated by nitrogen isotope diffusion. The samples were deposited using plasma-assisted pulsed laser deposition. Nitrogen concentration depth profiles were obtained from secondary-ion-mass spectrometry measurements, and in gas effusion measurements, the molecular nitrogen flux was measured as a function of the heating rate. Measurements performed on sample stacks that were doped with isotopically enriched 15N and 14N in the top and bottom half of the samples, respectively, clearly demonstrate that nitrogen diffusion is governed by atomic diffusion and molecules are formed primarily at the sample surface. At high nitrogen concentrations, the diffusion coefficient, D, is thermally activated, while for low concentration diffusion, D is independent of temperature. The data can be described by a model, where N diffusion occurs between minimum energy positions by surmounting the barrier between sites at a saddle point. Separated in energy from the transport sites are deep levels with a concentration of ≈1018 cm−3. For high-concentration diffusion, the N chemical potential, μN, resides at ≈1.36 eV below the migration saddle point. For low concentration diffusion, μN shifts deeper in energy with a rate of ≈2.8 meV/K as the temperature increases. From N effusion data, the nitrogen density-of-states is derived. For high N concentration diffusion, two peaks are observed at ES–μN = −0.93 and −1.26 eV, while for low N concentration diffusion, a prominent peak at ES–μN = −1.63 eV occurs. Applying density functional theory calculations, different microscopic diffusion mechanisms are evaluated, and the corresponding transition states are derived. [ABSTRACT FROM AUTHOR]

Hydrogen bonding in β-Ga2O2 is investigated using hydrogen effusion measurements. The samples were grown by plasma-assisted pulsed laser deposition. With increasing deposition temperature, the total H concentration decreases from 8.1 × 1019 to 9.2 × 1018 cm−3. The dependence of the hydrogen chemical potential, μH, on the H concentration is derived from the effusion spectra and subsequently used to determine the H density-of-states distribution. β-Ga2O2 deposited at Tdep ≤ 723 K exhibits a needle-like peak in the H density-of-states distribution at ≈1.8 eV below the H transport states. With increasing Tdep, the H density-of-states changes and two broad peaks emerge that are located at ≈1.7 and 2.4 eV below the H transport states for Tdep ≥ 873 K. [ABSTRACT FROM AUTHOR]

In the first longitudinal, population-based study of full-day kindergarten (FDK) outcomes beyond primary school in Canada, we used linked administrative data to follow 15 kindergarten cohorts (n ranging from 112 to 736) up to grade 9. Provincial assessments conducted in grades 3, 7, and 8 and course marks and credits earned in grade 9 were compared between FDK and half-day kindergarten (HDK) students in both targeted and universal FDK programmes. Propensity score matched cohort and stepped-wedge designs allowed for stronger causal inferences than previous research on FDK. We found limited long-term benefits of FDK, specific to the type of programme, outcomes examined, and subpopulations. FDK programmes targeted at low-income areas showed long-term improvements in numeracy for lower income girls. Our results suggest that expectations for wide-ranging long-term academic benefits of FDK are unwarranted.

We investigated the influence of the emitter (amorphous-Si, a-Si, or polythiophene derivatives: poly(3-hexylthiophene), P3HT, and poly(3-[3,6-dioxaheptyl]-thiophene), P3DOT) and the interface passivation (intrinsic a-Si or SiOX and methyl groups or SiOX) on the c-Si based 1×1 cm2 planar hybrid heterojunction solar cell parameters. We observed higher short circuit currents for the P3HT or P3DOT/c-Si solar cells than those obtained for a-Si/c-Si devices, independent of the interface passivation. The obtained VOC of 659mV for the P3DOT/SiOX/c-Si heterojunction solar cell with hydrophilic 3,6-dioxaheptyl side chains is among the highest reported for c-Si/polythiophene devices. The maximum power conversion efficiency, PCE, was 11% for the P3DOT/SiOX/c-Si heterojunction solar cell. Additionally, our wafer lifetime measurements reveal a field effect passivation in the wafer induced by the polythiophenes when deposited on c-Si. [ABSTRACT FROM AUTHOR]

The influence of post-hydrogenation on the electrical and optical properties of solid phase crystallized polycrystalline silicon (poly-Si) was examined. The passivation of grain-boundary defects was measured as a function of the passivation time. The silicon dangling-bond concentration decreases with increasing passivation time due to the formation of Si-H complexes. In addition, large H-stabilized platelet-like clusters are generated. The influence of H on the electrical properties was investigated using temperature dependent conductivity and Hall-effect measurements. For poly-Si on Corning glass, the dark conductivity decreases upon hydrogenation, while it increases when the samples are fabricated on silicon-nitride covered Borofloat glass. Hall-effect measurements reveal that for poly-Si on Corning glass the hole concentration and the mobility decrease upon post-hydrogenation, while a pronounced increase is observed for poly-Si on silicon-nitride covered Borofloat glass. This indicates the formation of localized states in the band gap, which is supported by sub band-gap absorption measurments. The results are discussed in terms of hydrogen-induced defect passivation and generation mechanisms. [ABSTRACT FROM AUTHOR]

We report on the formation of self-organized structures in thin films of silicon-germanium (Si1-xGex) with 0.3

Raman measurements were performed on laser crystallized poly-Si on different substrates. Observed shifts of the Si LO-TO phonon peak are caused by stress originating from the film-substrate interface. The principal cause of the stress is the difference in the thermal expansion coefficients of substrate and film. Consequently, the amount of thermal stress critically depends on the choice of substrate. In the case of undoped samples on quartz, profiler and x-ray measurements confirmed the occurrence of tensile stress in the films. In the case of heavily doped samples, the change of the lattice parameter determined by x-rays is probably to a significant extend responsible for additional Raman shifts. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous silicon (a-Si:H) films on molybdenum coated glass substrates were crystallized using a XeCl excimer laser. Structural information on the resulting polycrystalline silicon (poly-Si) films was obtained from scanning electron microscopy and electron backscattering diffraction measurements. The average grain size varies with laser fluence. The maximum average grain size in the super lateral growth energy-density range is considerably smaller for poly-Si on Mo coated substrates than for poly-Si on quartz. In addition, the metal layer affects the laser fluence necessary to achieve super lateral growth. Samples crystallized under super lateral growth conditions show a preferential surface orientation along the {111} direction. Intermixing of Mo and silicon is not observed. [ABSTRACT FROM AUTHOR]

The grain boundary populations in laser crystallized polycrystalline silicon thin films are determined by electron microscope analysis, using electron backscattering contrast in the scanning electron microscope, and convergent beam electron diffraction in the transmission electron microscope. The grain boundary populations of the grains larger than 0.5 μm are dominated by first and second order twin boundaries. This result is found to be a general feature of laser crystallization independent of the experimental details of the laser crystallization process. Texture analysis of the laser crystallized poly-Si films shows that under certain experimental conditions a {111}-preferential orientation of the grains perpendicular to the substrate can be obtained. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using infrared absorption spectroscopy of hydrogen passivated β-Ga2O3 the temperature dependence of the dominant O – H vibrational line was measured between 5 and 300 K. With increasing temperature, the vibrational line shifts by Δω = 7.8 cm-1 to lower frequency. This is accompanied by a broadening of the vibrational line from Γ = 0.61 to 8.18 cm-1. The data are discussed in terms of elastic and inelastic phonon scattering and exchange coupling. Moreover, the perturbation of the hydrogen potential is evaluated. [ABSTRACT FROM AUTHOR]