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Presents information on a study that used an optical modulation technique to observe the electromodulation of photoluminescence (PL) in single and multiple quantum wells. Discussion on the photomodulated PL spectra of quantum-well samples; Cause of the modulation of the optical constants in a semiconductor; Conclusion.

We present spectroscopic ellipsometry (SE) results, in the 0.75–5 eV spectral range, obtained on highly uniform Ta2O5 coatings deposited on high-quality silica substrates by ion sputtering. The study was motivated mainly by issues related to the exploitation of Ta2O5–SiO2λ/4 multilayers in detectors of gravitational waves. Two sets of samples with nominal thicknesses of 40 and 500 nm were considered. A sub-set of samples was treated with post-growth annealing in air for several hours at temperatures Tann up to 600 °C. The SE data were complemented with photothermal common-path interferometry measurements at 1064 nm providing data about absorption losses in the 1–4 ppm range. SE data, taken at room temperature, were analysed by exploiting three different three-phase (substrate/film/surface) models (Cody–Lorentz, Tauc–Lorentz and Herzinger–Johs) of the fundamental absorption edge. Following the literature (Stenzel 2009 J. Phys. D: Appl. Phys.42 055312) the simulations exploited a graded nano-porosity inside the coating, testing both the shape and composition of the pores. The best simulation of data was obtained using the Cody–Lorentz approach and a quasi-uniform density (6–7.5%) of empty spherical pores, slowly degrading from the substrate/film interface towards the film/ambient interface. A comparison with the literature indicated a high stoichiometric quality of the coatings. The analysis of samples annealed to increasingly higher Tann showed (i) a slight blue-shift of the energy gap (ii) an increase in the pore volume fraction, (iii) an increase (1–2%) in the coating thickness, (iv) a small (less than 1%) reduction in the index of refraction in the transparency region and (v) a limited increase in absorption losses. These findings were interpreted in terms of a release of the compressive strain inherent to the deposition process. [ABSTRACT FROM AUTHOR]

Surface plasmonic-enhanced light trapping from metal nanoparticles is a promising way of increasing the light absorption in the active silicon layer and, therefore, the photocurrent of the silicon solar cells. In this paper, we applied silver nanoparticles on the rear side of polycrystalline silicon thin film solar cell and systematically studied the dielectric environment effect on the absorption and short-circuit current density (Jsc) of the device. Three different dielectric layers, magnesium fluoride (MgF, n = 1.4), tantalum pentoxide (TaO, n = 2.2), and titanium dioxide (TiO, n = 2.6), were investigated. Experimentally, we found that higher refractive index dielectric coatings results in a redshift of the main plasmonic extinction peak and higher modes were excited within the spectral region that is of interest in our thin film solar cell application. The optical characterization shows that nanoparticles coated with highest refractive index dielectric TiO provides highest absorption enhancement 75.6 %; however, from the external quantum efficiency characterization, highest short-circuit current density Jsc enhancement of 45.8 % was achieved by coating the nanoparticles with lower refractive index MgF. We also further optimize the thickness of MgF and a final 50.2 % Jsc enhancement was achieved with a 210-nm MgF coating and a back reflector. [ABSTRACT FROM AUTHOR]