The effects of the quantum well (QW) width, carrier density, and aluminium (Al) concentration in the barrier layers on the optical characteristics of a gallium nitride (GaN)-based QW laser diode are investigated by means of a careful modelling analysis in a wide range of temperatures. The device’s optical gain is calculated by using two different band energy models. The first is based on the simple band-to-band model that accounts for carrier transitions between the first levels of the conduction band and valence band, whereas the second assumes the perturbation theory (k.p model) for considering the valence intersubband transitions and the relative absorption losses in the QW. The results reveal that the optical gain increases with increasing the n-type doping density as well as the Al molar fraction of the Al
x
Ga1–x
N layers, which originate the GaN compressive-strained QW. In particular, a significant optical gain on the order of 5000 cm–1 is calculated for a QW width of 40 Å at room temperature. In addition, the laser threshold current density is of few tens of A/cm2 at low temperatures.
The subject of this work is to evaluate the influence and adhesion degree of different coating layers deposited on a ductile cast iron substrate by two different methods, thermal spraying and welding with and without use of an interlayer. Microstructures of different zones and interfaces of coated specimens are investigated using optical microscope and scanning electron microscope SEM. Also, the mechanical behavior was evaluated by tensile test. It is found that when stainless steel thermal spraying coating onto the ductile cast iron substrate, the use of the nickel-based interlayer Ni allowed us to mitigate the disadvantages of cracking at the interface. This is due to the mechanical effect of nickel plasticity. In the case of coating by welding, the use of nickel-based buttering ENi-CI allowed us to reduce the diffusion of graphite to stainless steel, resulting in a reduction in the formation of harder alloy carbides. Finally, the mechanicals tests in particular the tensile test shows that the coating by welding is effective but causes a structural hardening; on the other hand the coating realized by thermal spraying does not really present sufficient adhesion.
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