InGaN/GaN quantum wells (QWs) were grown by molecular-beam epitaxy on c-plane sapphire substrates. The growth of InGaN is carried out at 550 °C with a large V/III ratio to counteract the low efficiency of NH3 at that temperature and to promote the two-dimensional mode of growth. An In composition of 16%±2% was determined by high-resolution x-ray diffraction experiments. Room-temperature photoluminescence of InGaN/GaN single QWs can be obtained over the whole visible spectrum (from 0.4 to 0.66 μm) by varying the well thickness from 1 to 5 nm. These heterostructures exhibit very large Stokes shifts between the emission and the absorption edge energies.

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Spectroscopic ellipsometry (SE) carried out at 300 K together with reflectivity measurements performed from 5 to 300 K are used to determine the temperature dependence of the refractive index of hexagonal GaN films between 360 and 600 nm. The refractive index is well described with a Sellmeier dispersion law and its variation with temperature is given. Below the band gap, the three excitonic features (labelled A, B and C) appearing in the reflectivity spectra are analysed within a multi-polariton model which includes the spatial dispersion. The transition energy, broadening parameter and oscillator strength are derived. The temperature dependence of A and B broadening parameters is analysed.

GaInN and GaN were grown by molecular beam epitaxy on c-plane sapphire using NH3. 9 K photoluminescence performed on both GaInN thin layers and GaInN/GaN multiple-quantum wells (MQWs) exhibits narrow emission (∼50 meV linewidths). Transmission electron microscopy images show sharp GaInN/GaN interfaces and homogeneous GaInN layers. Strong indium surface segregation is also evidenced. Light-emitting diodes were fabricated from 5×GaInN (25 Å)/GaN (35 Å) MQW heterostructures. The 300 K electroluminescence yields blue light at 440 nm.

Partial polarization may be the result of a scattering process from a fully polarized incident beam. It is shown how the "loss of polarization" is connected with the nature of scatterers (surface roughness, bulk heterogeneity) and on the receiver solid angle. These effects are theoretically predicted and confirmed via multiscale polarization measurements in the speckle pattern of rough surfaces. "Full" polarization can be recovered when reducing the receiver aperture.

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The dielectric function of Si nanoparticles embedded in silica has been determined from spectroscopic ellipsometry and photothermal deflexion spectroscopy from 0.7to6eV. The influence of crystalline fraction and diameter of the nanoparticles on their optical properties has been investigated. Above 4nm of diameter, the nanoparticles presented a dielectric function similar to that of fine grained polycrystalline Si (poly-Si) at photon energy higher than 2eV, with the well marked structures associated with the E1 and E2 critical points. In contrast, below 2eV their absorption coefficient was smaller than for poly-Si. Below 2.5nm of diameter, the dielectric function of the nanoparticles drastically changed. The magnitude of the imaginary part of the dielectric function of the nanoparticles near the position of the E1 critical point constantly decreased, whereas it increased at the position of the E2 critical point. These observations can be interpreted as the result of the transfer of the oscillator strength of the low energy states to the high energy states as the diameter of the nanoparticles decreases. The states associated with the fundamental indirect gap are slowly blueshifted when the diameter of the nanoparticles decreased, as evidenced by photoluminescence measurements.

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