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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 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]

The role that the mother substrate plays to influence the performance of InGaN/GaN-based light-emitting diodes (LEDs) onto the adhesive flexible tapes is addressed in this letter. For this purpose, the electroluminescent (EL) spectra and current density–voltage ( $J$ – $V$ ) characteristics of flexi-LEDs are studied under different convex bending configurations (from a curvature radius of infinity to 1.4 cm), showing only one peak around 442 nm in all the cases. Both the EL spectra and $J$ – $V$ characteristics are affected by the applied tensile stress when the flexi-LED is bent. In fact, an increase of the applied tensile strain from 0.02% to 0.09% results in a red-shift of the EL peak energy by 3 meV at 0.7 mA, and a drop of the current at high forward bias. In addition, such flexi-LEDs exhibit a reversible response when a significant mechanical deformation is applied. [ABSTRACT FROM PUBLISHER]

(Ga,In)N/GaN multiple quantum well blue light emitting diodes (LEDs) grown on mesa-patterned silicon substrates with improved electro-optic characteristics are demonstrated. The active regions are grown on top of high-reflectivity AlN/(Al,Ga)N distributed Bragg reflectors (DBRs). Due to efficient stress relaxation at the mesa edges, crack formation during growth or upon the post-growth cooling-down of the samples can be avoided. A large number of AlN/(Al,Ga)N bilayers in the DBR can be then included in the LED structures leading to strong enhancement of the LED device output power in spite of the presence of the absorbing silicon substrate at the LED emission wavelength. Photograph of a blue light emitting diode ( I = 20 mA) grown on top of a high reflectivity distributed Bragg reflector on a mesa-patterned silicon substrate. [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]