Room temperature photoluminescence at 1.6μm is demonstrated from InGaAs quantum dots capped with an 8nm GaAsSb quantum well. Results obtained from various sample structures are compared, including samples capped with GaAs. The observed redshift in GaAsSb capped samples is attributed to a type II band alignment and to a beneficial modification of growth kinetics during capping due to the presence of Sb. The sample structure is discussed on the basis of transmission electron microscopy results.

Thin silicon carbide films have been deposited by chemical vapor deposition on p-type (100) silicon substrates. The composition and bonds formed in these films have been analyzed by x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy. The native surface oxide on the silicon carbide surface induced by air exposure has also been studied. Several phases are detected in the near-surface region: elemental Si, Si oxides (mainly SiO2), Si carbide (SiC) and Si oxicarbides (SiOxCy). Quantitative XPS analysis results indicate that, for atomic oxygen fractions <0.15, the Si–C phases are dominant in the films. Above this value no silicon oxicarbide is observed, but a multiphase material formed by elemental Si, Si oxides and Si carbides is observed. In spite of the film being a complex phase mixture, a simple relationship is found between the overall carbon and oxygen compositions. The carbon atomic fraction in the film decreases quasilinearly as the oxygen content increases, with a slope of about −1. An overall composition of SiOxC3−x in the 0.5<x<2 range is found for the phase mixture. A comparison with silicon carbide obtained by CHn+ ion implantation into monocrystalline silicon is made.

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Due to spectral sensitivity effects, using a single standard spectrum leads to a large uncertainty when estimating the yearly averaged photovoltaic efficiency or energy yield. Here we demonstrate how machine learning techniques can reduce the yearly spectral sets by three orders of magnitude to sets of a few characteristic spectra, and use the resulting proxy spectra to find the optimal solar cell designs maximizing the yearly energy production. When using standard conditions, our calculated efficiency limits show good agreement with current photovoltaic efficiency records, but solar cells designed for record efficiency under the current standard spectra are not optimal for maximizing the yearly energy yield. Our results show that more than 1 MWh m−2 year−1 can realistically be obtained from advanced multijunction systems making use of the direct, diffuse, and back-side albedo components of the irradiance.