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We present our research on fabrication and structural and transport characterization of ultrathin superconducting NbN layers deposited on both single-crystal Al2O3 and Si wafers, and SiO2 and Si3N4 buffer layers grown directly on Si wafers. The thicknesses of our films varied from 6 nm to 50 nm and they were grown using reactive RF magnetron sputtering on substrates maintained at the temperature 850• C. We have performed extensive morphology characterization of our films using the X-ray diffraction method and atomic force microscopy, and related the results to the type of the substrate used for the film deposition. Our transport measurements showed that even the thinnest, 6 nm thick NbN films had the superconducting critical temperature of 10-12 K, which was increased to 14 K for thicker films.

We demonstrate a semiconductor double-chirped mirror consisting of an AlAs/GaAs multilayer stack grown by molecular beam epitaxy. The mirror has a high negative group velocity dispersion of −2450 ± 100 fs2 and a reflectivity exceeding 98.9% over the spectral range spanning ±4 nm around 1035 nm. When used to compensate the cavity dispersion in a diode-pumped femtosecond Yb:KY(WO4)2 oscillator, at 490 mW of the absorbed pump power, the laser delivered 110 mW in pulses of 240 fs duration.

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In this work, we investigate the optical properties and passivation effects of silicon nitride stacks deposited by the plasma enhanced chemical vapor deposition (PECVD) system. A stack of three SiNx:H layers with different refractive indices were deposited at 310 °C using silane (SiH4) and ammonia (NH3) as precursor gases. The chemical composition of the films was modulated by varying the gas flow ratio r = [NH3]/[SiH4]. Details of the optical optimization procedure are presented. Thanks to spectrophotometric and spectroscopic ellipsometry measurements we confirmed the suitability of a three layered SiNx:H stack for antireflective coating. Passivation effects were evaluated by measurements of effective carrier lifetimes. Simulated short‐circuit currents were also calculated for two fixed internal quantum efficiency IQE spectra. It was found that a triple‐layered silicon nitride coating provides lower optical reflection and better passivation for silicon p‐type than those of a single‐layered silicon nitride coating.