Effect of Growth Temperature on the Structural and Morphological Properties of MgCdO Thin Films Grown by Metal Organic Chemical Vapor Deposition

II-VI oxides ternary alloys have attracted considerable interest of the scientific community due to the possibility of modulating their interesting optoelectronic properties. Despite this interest, MgCdO has been poorly studied. In this work, by using the metal organic chemical vapor deposition method at low pressure, we have analyzed the synthesis of thin films of this alloy. Thus, for a fixed metal-organic precursors content, a change from Mg1-xCdxO (Mg-rich phase) to Cd1-xMgxO (Cd-rich phase) has been induced when decreasing the growth temperature. The temperature range where both phases coexist has been particularly analyzed. Using X-ray diffraction analysis and scanning electron microscopy, a structural and morphological study of the samples has been carried out. In addition, the composition of the alloy has been measured by using energy dispersive X-ray analysis, and the behavior of the lattice parameter as a function of Cd content has been studied

p-Type Ultrawide-Band-Gap Spinel ZnGa2O4: New Perspectives for Energy Electronics

The family of spinel compounds is a large and important class of multifunctional materials of general formulation AB2X4 with many advanced applications in energy and optoelectronic areas such as fuel cells, batteries, catalysis, photonics, spintronics, and thermoelectricity. In this work, it is demonstrated that the ternary ultrawide-band-gap (∼5 eV) spinel zinc gallate (ZnGa2O4) arguably is the native p-type ternary oxide semiconductor with the largest Eg value (in comparison with the recently discovered binary p-type monoclinic β-Ga2O3 oxide). For nominally undoped ZnGa2O4 the high-temperature Hall effect hole concentration was determined to be as large as p = 2 × 1015 cm–3, while hole mobilities were found to be μh = 7–10 cm2/(V s) (in the 680–850 K temperature range). An acceptor-like small Fermi level was further corroborated by X-ray spectroscopy and by density functional theory calculations. Our findings, as an important step toward p-type doping, opens up further perspectives for ultrawide-band-gap bipolar spinel electronics and further promotes ultrawide-band-gap ternary oxides such as ZnGa2O4 to the forefront of the quest of the next generation of semiconductor materials for more efficient energy optoelectronics and power electronics

Measuring macroscopic brain connections in vivo

Decades of detailed anatomical tracer studies in non-human animals point to a rich and complex organization of long-range white matter connections in the brain. State-of-the art in vivo imaging techniques are striving to achieve a similar level of detail in humans, but multiple technical factors can limit their sensitivity and fidelity. In this review, we mostly focus on magnetic resonance imaging of the brain. We highlight some of the key challenges in analyzing and interpreting in vivo connectomics data, particularly in relation to what is known from classical neuroanatomy in laboratory animals. We further illustrate that, despite the challenges, in vivo imaging methods can be very powerful and provide information on connections that is not available by any other means

Crystal facet engineering in Ga-doped ZnO nanowires for mid-IR plasmonics (Conference Presentation)

International audienc

Effects of thermal emission and re-trapping of photo-injected carriers on the optical transitions of InAs/GaAs quantum dots

International audiencePhotoluminescence (PL) measurements are presented for self-assembled InAs/GaAs quantum dots (QDs). Under a very low excitation density, the 8K-PL spectrum of the QD sample shows two well-defined sub-bands. The PL sub-bands are clarified as emissions from the ground state (GS) and the first excited state (FES) of the dots. Different from that of the FES transition, a sigmoidal temperature-dependent variation is observed from the integrated PL intensity (IPLI) of the GS transition. This behavior is related to the carrier exchange between the excited states and the GS of the dots. A simple rate equation model, which takes into account the effects of the thermal escape and re-trapping of photo-injected carriers, is proposed to describe the sigmoidal variation of the IPLI. A good agreement between the model simulation and the experimental results is obtained and therefore supports the argument for the carrier exchange between the excited states and the ground states

Electron beam dose dependence of surface recombination velocity and surface space charge in semiconductor nanowires

International audienc

Cross-section imaging and p-type doping assessment of ZnO/ZnO:Sb core-shell nanowires by scanning capacitance microscopy and scanning spreading resistance microscopy

International audienc

Characterization of sol gel Zn1-xCaxO thin layers deposited on p-Si substrate by spin-coating method

International audienceThin films Zn1-xCaxO (0≤x≤6%) on a p-Si substrate are elaborated by sol-gel process and spin coating. X-ray diffraction displays a hexagonal wurtzite structure with an increase of lattice parameters confirming the substitution of Zn 2+ by Ca 2+. The estimation of crystallite sizes along the three main crystallographic planes is practically constant (22 nm) suggesting a spherical symmetry shape of the crystallites which is confirmed by SEM. UV-visible reflectance spectra attest a band gap tuning from 3.144 to 3.262 eV which is confirmed by the PL measurement at 2 K for Zn0.94Ca0.06O sample by the appearance of a broad band around 3.508 eV. Although the luminescence of the samples is weak, we well distinguish the free exciton emission (FXA) positioned at 3.376 eV and the bound exciton recombination (D 0 X) around 3.362 eV

Resolving ZnO-based coaxial core-multishell heterostructure by electrical scanning probe microscopy

International audienc

An explanation for the non-monotonic temperature dependence of the photoluminescence spectral features of self-organized InAs QDs

International audienceTemperature-dependent photoluminescence (PL) measurements under different excitation densities were performed on self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy. Non-monotonic evolutions in the curves of the PL spectral parameters as a function of the sample temperature were observed in the low-temperature regime. Indeed, the PL peak energy of the QDs shows a sigmoidal variation with increasing temperature. This component is accompanied by an anomalous increase in the integrated intensity over the temperature range of 8–50K. These behaviors have been attributed to the optical emission from deep states that exist in the potential of the dots. A simple rate equation model, which describes the thermally activated emission and trapping of photo-injected carriers, is proposed to illustrate the interpretations made regarding the evolution of the integrated PL intensity with increasing temperature. A good agreement between the model simulation and the PL data was obtained for temperatures ranging from 8 to 300K. It was found that the thermally activated process of the intra-dot redistribution of carriers provides a good description of the anomalous behaviors encountered in the PL investigations depending on the temperature of the QD sample