28 research outputs found
Wavelength-selective ultraviolet (Mg,Zn)O photodiodes: Tuning of parallel composition gradients with oxygen pressure
We report on ultraviolet photodiodes with integrated optical filter based on the wurtzite (Mg,Zn)O
thin films. Tuning of the bandgap of filter and active layers was realized by employing a
continuous composition spread approach relying on the ablation of a single segmented target in
pulsed-laser deposition. Filter and active layers of the device were deposited on opposite sides of a
sapphire substrate with nearly parallel compositional gradients. Ensure that for each sample position
the bandgap of the filter layer blocking the high energy radiation is higher than that of the
active layer. Different oxygen pressures during the two depositions runs. The absorption edge is
tuned over 360 meV and the spectral bandwidth of photodiodes is typically 100 meV and as low as
50 meV
Non-linear optical deformation potentials in uniaxially strained ZnO microwires
The emission properties of bent ZnO microwires with diameters ranging from 1.5 μm to 7.3 μm are
systematically investigated by cathodoluminescence spectroscopy at T ≈ 10 K. We induced
uniaxial strains along the c-axis of up to ±2.9 %. At these high strain values, we observe a nonlinear
shift of the emission energy with respect to the induced strain, and the magnitude of the
energy shift depends on the sign of the strain. The linear and non-linear deformation potentials
were determined to be D1=−2.50±0.05 eV and D2=−15.0±0.5 eV, respectively. The nonlinearity
of the energy shift is also reflected in the observed spectral broadening of the emission
peak as a function of the locally induced strain, which decreases with increasing strain on the compressive
side and increases on the tensile side
Visible-blind and solar-blind ultraviolet photodiodes based on (InxGa1-x)2O3
UV and deep-UV selective photodiodes from visible-blind to solar-blind were realized based on a
Si-doped (InxGa1–x)2O3 thin film with a monotonic lateral variation of 0.0035<x<0.83. Such
layer was deposited by employing a continuous composition spread approach relying on the ablation
of a single segmented target in pulsed-laser deposition. The photo response signal is provided
from a metal-semiconductor-metal structure upon backside illumination. The absorption onset was
tuned from 4.83 to 3.22 eV for increasing x. Higher responsivities were observed for photodiodes
fabricated from indium-rich part of the sample, for which an internal gain mechanism could be
identified. VC 2016 AIP Publishing LLC
Competing exciton localization effects due to disorder and shallow defects in semiconductor alloys
We demonstrate that excitons in semiconductor alloys are subject
to competing localization effects due to disorder (random potential fluctuations)
and shallow point defects (impurities). The relative importance of these effects
varies with alloy chemical composition, impurity activation energy as well as
temperature. We evaluate this effect quantitatively for MgxZn1−xO : Al (0 6
x 6 0.058) and find that exciton localization at low (2 K) and high (300 K)
temperatures is dominated by shallow donor impurities and alloy disorder,
respectively
Lattice parameters and Raman-active phonon modes of β-(AlxGa1−x)2O3
We present X-ray diffraction and Raman spectroscopy investigations of a (100)-oriented
(AlxGa1–x)2O3 thin film on MgO (100) and bulk-like ceramics in dependence on their composition.
The thin film grown by pulsed laser deposition has a continuous lateral composition spread allowing
to determine precisely the dependence of the phonon mode properties and lattice parameters on
the chemical composition. For x<0.4, we observe the single-phase b-modification. Its lattice parameters
and phonon energies depend linearly on the composition. We determined the slopes of
these dependencies for the individual lattice parameters and for nine Raman lines, respectively.
While the lattice parameters of the ceramics follow Vegard’s rule, deviations are observed for the
thin film. This deviation has only a small effect on the phonon energies, which show a reasonably
good agreement between thin film and ceramics
Lattice parameters and Raman-active phonon modes of (InxGa1–x)2O3 for x < 0.4
We present X-ray diffraction and Raman spectroscopy investigations of (InxGa1–x)2O3 thin films
and bulk-like ceramics in dependence of their composition. The thin films grown by pulsed laser
deposition have a continuous lateral composition spread allowing the determination of phonon
mode properties and lattice parameters with high sensitivity to the composition from a single 2-in.
wafer. In the regime of low indium concentration, the phonon energies depend linearly on the composition
and show a good agreement between both sample types. We determined the slopes of these
dependencies for eight different Raman modes. While the lattice parameters of the ceramics follow
Vegard’s rule, deviations are observed for the thin films. Further, we found indications of the highpressure
phase InGaO3 II in the thin films above a critical indium concentration, its value depending
on the type of substrate
<scp>ReSurveyEurope</scp>: A database of resurveyed vegetation plots in Europe
AbstractAimsWe introduce ReSurveyEurope — a new data source of resurveyed vegetation plots in Europe, compiled by a collaborative network of vegetation scientists. We describe the scope of this initiative, provide an overview of currently available data, governance, data contribution rules, and accessibility. In addition, we outline further steps, including potential research questions.ResultsReSurveyEurope includes resurveyed vegetation plots from all habitats. Version 1.0 of ReSurveyEurope contains 283,135 observations (i.e., individual surveys of each plot) from 79,190 plots sampled in 449 independent resurvey projects. Of these, 62,139 (78%) are permanent plots, that is, marked in situ, or located with GPS, which allow for high spatial accuracy in resurvey. The remaining 17,051 (22%) plots are from studies in which plots from the initial survey could not be exactly relocated. Four data sets, which together account for 28,470 (36%) plots, provide only presence/absence information on plant species, while the remaining 50,720 (64%) plots contain abundance information (e.g., percentage cover or cover–abundance classes such as variants of the Braun‐Blanquet scale). The oldest plots were sampled in 1911 in the Swiss Alps, while most plots were sampled between 1950 and 2020.ConclusionsReSurveyEurope is a new resource to address a wide range of research questions on fine‐scale changes in European vegetation. The initiative is devoted to an inclusive and transparent governance and data usage approach, based on slightly adapted rules of the well‐established European Vegetation Archive (EVA). ReSurveyEurope data are ready for use, and proposals for analyses of the data set can be submitted at any time to the coordinators. Still, further data contributions are highly welcome.</jats:sec
The Open-Access Journal for the Basic Principles of Diffusion Theory, Experiment and Application
IR Micro-imaging of mesoporous silicon as a model system for the investigation of hysteresis phenomen