We present a detailed analysis of inter- and intraband transitions in GaN/AlN self-organized quantum dots grown on sapphire, silicon (111) and 6H-SiC substrates. Quantum dot samples have been characterized by means of transmission electron microscopy, photoluminescence and photo-induced absorption spectroscopy. Interlevel transitions in the conduction band are observed in the 0.52–0.98 eV energy range, thus covering the telecommunication band. The s-pz absorption is peaked at 0.8 eV (0.52 eV) for samples with dot height of 1.5 nm (6 nm). Calculations show that in bigger dots the transition energy is governed by the value of the internal field.

In this work we report optical characterization on several cubic c-AlGaN layers grown by MBE on SiC on Si pseudo-substrates, with different aluminum concentrations ranging from 0 to 70 %. Excitation power evolution of AlGaN photoluminescence (PL) spectra as well as reflectivity spectra allow to attribute PL peak to band gap recombination. PL energy dependence versus aluminum concentration is given. Reflectivity investigations are performed in the energy range between 1.5 eV and 4 eV on the samples. Theoretical calculations of multilayered structure reflectivity are fitted to experimental results, allowing an accurate determination of refractive index evolution versus Al concentration. From this analysis, qualitative information about interface roughness at AlGaN/SiC is also be derived.

We present here a description and an analysis of the modifications in the growth behaviour of GaN induced by the presence of foreign species. The particular cases of Mg and Si are analysed. Profound changes, both in microscopic and macroscopic scales, occur in presence of Mg, even for fluxes of about 1/1000th of the Ga flux. The growth rate can be increased by almost 50%, depending of the III/V ratio and on the amount of Mg. A theoretical model is proposed to describe the observed effect. It is found that Mg induces changes in the Ga and N diffusion barriers and acts as a surfactant. The effect is stronger on the α-GaN than on the β-GaN, where N is more tightly bonded. The effect of Si is by far less pronounced, probably because it is more easily incorporated than Mg, and its effect on the surface kinetics is then strongly reduced.

We present here a description and an analysis of the modifications in the growth behaviour of GaN induced by the presence of foreign species. The particular cases of Mg and Si are analysed. Profound changes, both in microscopic and macroscopic scales, occur in presence of Mg, even for fluxes of about 1/1000th of the Ga flux. The growth rate can be increased by almost 50%, depending of the III/V ratio and on the amount of Mg. A theoretical model is proposed to describe the observed effect. It is found that Mg induces changes in the Ga and N diffusion barriers and acts as a surfactant. The effect is stronger on the a-GaN than on the α-GaN, where N is more tightly bonded. The effect of Si is by far less pronounced, probably because it is more easily incorporated than Mg, and its effect on the surface kinetics is then strongly reduced.

Thin films of hard, diamond-like, carbon have been deposited on glass, silicon and sapphire substrates using three different ion beam deposition techniques: (a) ion beam sputter-deposition from a graphite target, (b) sputter-deposition with simultaneous bombardment of the growing film using a second ion beam, (c) primary ion deposition using a beam extracted from an Ar-hydrocarbon plasma. Structural, mechanical optical and electrical properties were measured. It was found that the hydrogen content controlled the internal (compressive) stress and that relatively stress-free films contained ,∼ 30 atomic % H (average). The H content could be correlated with the H/C arrival ratio from the gas phase. Optical absorption and luminescence measurements gave a band gap of '∼, 1 ev with band-tailing. Resistivity measurements and their temperature dependence fitted variable range hopping models. Hardnesses were ≿ 7 Mohs. The properties of the films were consistent with a mixture of sp3 and sp2 bonds in an amorphous, hydrogenated structure.