143 research outputs found
High-field electron transport in doped ZnO
Current-voltage characteristics have been measured for ZnO:Ga and Zn:Sb epitaxial layers with electron densities ranging from 1.4x10(17) cm(-3) to 1.1 x 10(20) cm(-3). Two-terminal samples with coplanar electrodes demonstrate virtually ohmic behavior until thermal effects come into play. Soft damage of the samples takes place at high currents. The threshold power (per electron) for the damage is nearly inversely proportional to the electron density over a wide range of electron densities. Pulsed voltage is applied in order to minimize the thermal effects, and thus an average electric field of 150 kV cm(-1) is reached in some samples subjected to 2 ns voltage pulses. The results are treated in terms of electron drift velocity estimated from the data on current and electron density under the assumption of uniform electric field. The highest velocity of similar to 1.5 x 10(7) cm s(-1) is found at an electric field of similar to 100 kV cm(-1) for the sample with an electron density of 1.4 x 10(17) cm(-3). The nonohmic behavior due to hot-electron effects is weak, and the dependence of the electron drift velocity on the doping resembles the variation of mobility
Lattice parameters and electronic structure of BeMgZnO quaternary solid solutions: Experiment and theory
Enhancement of Be and Mg incorporation in wurtzite quaternary BeMgZnO alloys with up to 5.1 eV optical bandgap
Nondestructive atomic compositional analysis of BeMgZnO quaternary alloys using ion beam analytical techniques
The atomic composition with less than 1-2 atom % uncertainty was measured in
ternary BeZnO and quaternary BeMgZnO alloys using a combination of nondestructive
Rutherford backscattering spectrometry with 1 MeV He
+
analyzing ion beam and non-
Rutherford elastic backscattering experiments with 2.53 MeV energy protons. An
enhancement factor of 60 in the cross-section of Be for protons has been achieved to monitor
Be atomic concentrations. Usually the quantitative analysis of BeZnO and BeMgZnO systems
is challenging due to difficulties with appropriate experimental tools for the detection of the
light Be element with satisfactory accuracy. As it is shown, our applied ion beam technique,
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Accepted Manuscript
supported with the detailed simulation of ion stopping, backscattering, and detection
processes allows of quantitative depth profiling and compositional analysis of wurtzite
BeZnO/ZnO/sapphire and BeMgZnO/ZnO/sapphire layer structures with low uncertainty for
both Be and Mg. In addition, the excitonic bandgaps of the layers were deduced from optical
transmittance measurements. To augment the measured compositions and bandgaps of BeO
and MgO co-alloyed ZnO layers, hybrid density functional bandgap calculations were
performed with varying the Be and Mg contents. The theoretical vs. experimental bandgaps
show linear correlation in the entire bandgap range studied from 3.26 eV to 4.62 eV. The
analytical method employed should help facilitate bandgap engineering for potential
applications, such as solar blind UV photodetectors and heterostructures for UV emitters and
intersubband devices
Concerning Two-Level Structure of Potential Epidemic Hazard of the Mass Events with International Participation
The paper discusses epidemiological environment of particular countries and parts of the world viewed as potential platforms for mass events with international participation. It is established that the most unfavorable in this respect are Asian countries, primarily South-Eastern Asia ones, and African ones, from where the majority of well-known pandemics and epidemics have originated. Specified are the factors which are significant for spread of infectious diseases that can trigger emergency situation of sanitary epidemiological character of international concern. They are tourism and migration, trade and economic affairs, natural and anthropogenic disasters. The concept - “potential epidemic hazard of mass events with international participation” - is defined. It is demonstrated that its structure comprises two levels: the natural background of endemic and imported as related to mass event region epidemiological hazards, and epidemiological hazards imposed by the event itself. Outlined is a step-by-step algorithm for assessment of “potential epidemic hazard” of mass events with international participation allowing for adjustment of measures for the provision of sanitary and epidemiological welfare of the population
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