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Benefiting from exceptional credits voted in 1833, the Muséum national d’Hstoire naturelle de Paris had the opportunity to modernize the garden that houses it and was one with it: the Jardin des Plantes. The young architect Charles Rohault de Fleury (1801-1875), appointed a year earlier chief architect of the Museum, thus inherited the responsibility of designing new buildings and decorations that reflect the scientific ambition attached to this place: to preserve and exhibit all the natural productions of the globe. [ABSTRACT FROM AUTHOR]

Les propriétés germicides des rayonnements ultraviolets (UV) suscitent un intérêt de plus en plus important dans les domaines d'applications stratégiques que sont l'environnement et la santé. Les diodes électroluminescentes (LEDs) semi-conductrices à base de nitrure d'aluminium et de gallium représentent les nouvelles sources d'émission UV qui pourront répondre à cette demande. Leurs performances, bien qu'encore modestes, progressent chaque jour et nous vivons le point de bascule entre le laboratoire et le domaine grand public. Pour définitivement parvenir à s'imposer, elles doivent associer efficacité, forte capacité de développement, ainsi que souplesse et facilité d'utilisation, performances qu'aucune source UV n'a encore atteint jusqu'à présent. [ABSTRACT FROM AUTHOR]

The luminescence efficiency of AlxGa1−xN quantum dots (QDs) and quantum wells (QWs), buried in AlN cladding layers and emitting in the ultraviolet range between 234 and 310 nm, has been investigated. The growth and optical properties have been done using similar aluminum composition (varying from 0.4 to 0.75) for both QDs and QWs. In order to compare as much as possible the optical properties, the QWs were fabricated with a growth time tuned such that the QW width is similar to the average height of the QDs. The photoluminescence (PL) showed emission ranging from 4 to 5.4 eV, putting into evidence differences in terms of full width at half maximum, PL intensity, and asymmetry of the line shape between QDs and QWs. The results show shorter wavelengths and a slightly narrower PL linewidth for QWs. To determine the light emission dependence with the electric field direction in the crystal, the evolutions of the emission diagrams for all samples were recorded along two orthogonal directions, namely, the "in-plane" (growth) and the "on-side" directions, from which the light emission was collected. For the whole QDs and QWs samples' series, the shapes of the emission diagram indicate emission in both in-plane and on-side directions, as evidenced by intra-valence band mixings caused by strain effects combined with the anisotropic Coulomb interactions that are particularly contributing to the polarization at wavelengths below 260 nm. Furthermore, the degree of polarization, determined for each sample, showed good agreement with results from the literature. [ABSTRACT FROM AUTHOR]

The polarized photoluminescence emitted on the edge of a series of aluminum‐rich (Al,Ga)N‐AlN quantum wells (QWs) grown by molecular beam epitaxy on AlN templates deposited by metal organic chemical vapor deposition on c‐plane sapphire is measured. The contrast and the principal axis of the emission diagrams for 2 nm‐thick (Al,Ga)N QWs grown for aluminum compositions between 40% and 90% are studied. The light is emitted on the edge of the QWs at wavelengths going from 280 nm down to 209 nm. The emission diagram, a change from oblate to prolate with respect to the in‐plane orientation, for an aluminum composition is found to occur around 72%, that is, at an emission wavelength of about 235 nm. The orientations and shapes of the edge‐emission diagrams indicate that the fluctuations of the composition of the (Al,Ga)N confining layer are deep enough for producing intravalence band mixings. This property, that acts in concert with the built‐in strain and quantum‐confined Stark effect, contributes to the anisotropy of the light emission when the aluminum composition reaches 60–70%, that is, for an emission wavelength of 260–235 nm. [ABSTRACT FROM AUTHOR]

Aluminium Gallium Nitride (AlyGa1-yN) quantum dots (QDs) with thin sub-µm AlxGa1-xN layers (with x > y) were grown by molecular beam epitaxy on 3 nm and 6 nm thick hexagonal boron nitride (h-BN) initially deposited on c-sapphire substrates. An AlN layer was grown on h-BN and the surface roughness was investigated by atomic force microscopy for different deposited thicknesses. It was shown that for thicker AlN layers (i.e., 200 nm), the surface roughness can be reduced and hence a better surface morphology is obtained. Next, AlyGa1-yN QDs embedded in Al0.7Ga0.3N cladding layers were grown on the AlN and investigated by atomic force microscopy. Furthermore, X-ray diffraction measurements were conducted to assess the crystalline quality of the AlGaN/AlN layers and examine the impact of h-BN on the subsequent layers. Next, the QDs emission properties were studied by photoluminescence and an emission in the deep ultra-violet, i.e., in the 275–280 nm range was obtained at room temperature. Finally, temperature-dependent photoluminescence was performed. A limited decrease in the emission intensity of the QDs with increasing temperatures was observed as a result of the three-dimensional confinement of carriers in the QDs. [ABSTRACT FROM AUTHOR]

In the case of molecular beam epitaxy (MBE), the Mg acceptors are electrically active in the as‐grown material and a priori no additional annealing procedure is necessary. However, there are still some peculiarities in the electrical properties of ammonia‐process grown GaN:Mg and some annealing effect can be observed. Additionally, the character of weak temperature dependence in the vicinity of room temperature suggests that to describe the conduction process an additional conduction channel not related to the free carriers in the valence band must be taken into account. For these reasons, this article presents the results of low‐temperature resistivity and Hall Effect studies of Mg‐doped, ammonia‐process‐grown GaN. The studied samples are grown on low‐temperature buffers of GaN deposited on a sapphire substrate. High‐temperature annealing process (≈800 K) is carried out for all of them. The temperature dependences of the electrical transport properties before and after the annealing procedure are especially investigated at temperatures ranging from 10 up to 300 K. It is found that the low temperatures transport properties are sensitive to the annealing procedure and to describe the observed effects the hopping phenomena must be taken into account. [ABSTRACT FROM AUTHOR]

In this study, AlN epilayers were grown by ammonia-assisted molecular beam epitaxy on 3 nm h-BN grown on c-sapphire substrates. Their structural properties were investigated by comparing as-grown and postgrowth annealed layers. The role of annealing on the crystalline quality and surface morphology was studied as a function of AlN thickness and the annealing duration and temperature. Optimum annealing conditions were identified. The results of X-ray diffraction showed that optimization of the annealing recipe led to a significant reduction in the symmetric (0 0 0 2) and skew symmetric (1 0 −1 1) reflections, which was associated with a reduction in edge and mixed threading dislocation densities (TDDs). Furthermore, the impact on the crystalline structure of AlN and its surface was studied, and the results showed a transition from a surface with high roughness to a smoother surface morphology with a significant reduction in roughness. In addition, the annealing duration was increased at 1650 °C to further understand the impact on both AlN and h-BN, and the results showed a diffusion interplay between AlN and h-BN. Finally, an AlN layer was regrown on the top of an annealed template, which led to large terraces with atomic steps and low roughness. [ABSTRACT FROM AUTHOR]

High quality single crystalline n-type ZnO films, with a thickness of 200 nm, were grown on top of AlN/GaN layers under 25 W, 50 W and 100 W sputtering powers. The AlN and p-type GaN layers were deposited by metalorganic chemical vapor deposition (MOCVD). From X-ray diffraction measurements, the samples exhibited the (000 l) peaks corresponding to both ZnO, GaN and AlN monocrystalline layers. As the sputtering power was increased, the ZnO grain size increased and the dislocation density decreased. This result is supported by a reduction of the rms values obtained on the ZnO layers from Atomic Force Microscopy (AFM) results. In addition, photoluminescence peaks of ZnO at 372 nm, 375 nm and 380 nm were seen as dependent on the sputtering power. We have used an AlN electron blocking layer between ZnO and GaN films to improve the electroluminescence from the n-ZnO side. Room temperature electroluminescence (EL) of the LEDs demonstrated near UV-blue emission consisting of predominating peaks centred at 405 nm, 390 nm and 380 nm for the device with ZnO deposited at 25 W, 50 W and 100 W sputtering powers, respectively. Moreover, the I-V curves of the LEDs showed a rectifying behavior with 6.8 V, 6.4 V, 5.2 V threshold voltages for 25 W, 50 W and 100 W values. AlN/GaN/AlN/ZnO Tandem LED [Display omitted] • We presented a comprehensive and fine-tuned measurements and calculations of the n-ZnO/AlN/p-GaN/AlN hybrid type LEDs fabricated with 25 W, 50 W and 100 W sputtering powers of ZnO films. We have shown how a strong sputtering power such as 100 W has a curative effect on the crystallization of ZnO, • The intentionally used AlN electron blocking layer sandwiched between GaN and ZnO served as both a better nucleation of GaN and passivation layer, which can lead to a superior current spreading over the entire active area, and this combined with ZnO produced at high sputtering power was performed to further improve the efficiency of LED with higher and stronger light emission intensity than a conventional LED. • In this design, by depositing the AlN nucleation layer, we have also prevented the interphase, which has many insulating roles like GaOx. Thus, a better current transmissio- mechanism has been formed. • We fabricated the ZnO/GaN heterojunction with the AlN EBL layer by utilizing the continuous innovations in device fabrication techniques and analyzed in detail different application parameters such as crystallite sizes, dislocation densities and tensile stress including surface mechanisms all derived with XRD analysis. The Electroluminescence results were examined that light emission shifted from the blue region to near UV when switching from 25 W to 100 W. • The conclusions were supported by the energy band diagram by using the Anderson model, the energy barrier for electrons ΔEC, and holes ΔEV, at the interface of ZnO/AlN and GaN/AlN were obtained. Hall effect and secondary ion mass spectroscopy (SIMS) measurements were taken before and after AlN growth were obtained to explain the effects of possible H- and C- impurities, and our results show a remarkable difference in hole concentration and resistivity values. [ABSTRACT FROM AUTHOR]

• Selective sublimation of p-GaN is developed to fabricate enhancement-mode HEMTs. • AlGaN regrowth drastically reduces access resistances in enhancement-mode HEMTs. • Sublimation and regrowth are combined to co-integrate E/D-mode GaN HEMTs. In the present study, the selective sublimation of the p-GaN cap layer of Al(Ga)N/GaN HEMTs is developed to replace the commonly used dry etching with no risk of damage in the barrier layer in order to fabricate enhanced mode transistors. Thanks to this approach, enhancement-mode transistors are fabricated with a threshold voltage between 0 V and +1.5 V depending on the barrier layer aluminum molar fraction and thickness. Furthermore, we show the benefit of the combination of selective sublimation with the regrowth of AlGaN to reduce access resistance in these transistors which can be co-integrated with depletion-mode devices fabricated in the same process in areas where p-GaN has been totally evaporated. [ABSTRACT FROM AUTHOR]

• Selective sublimation of p-GaN is developed to fabricate enhancement-mode HEMTs. • AlGaN regrowth drastically reduces access resistances in enhancement-mode HEMTs. • Sublimation and regrowth are combined to co-integrate E/D-mode GaN HEMTs. We report on the fabrication of an enhancement mode p-GaN/AlN/GaN high electron mobility transistor with selective area sublimation under vacuum of the p-GaN cap layer. The GaN evaporation selectivity is demonstrated on the thin 2 nm AlN barrier layer. Furthermore, the regrowth of AlGaN is a major key to increase the maximum drain current in the transistors and enables the co-integration with depletion mode devices. [ABSTRACT FROM AUTHOR]