Vasileios Nikas

White light emission from amorphous silicon oxycarbide (a-SiCxOy) thin films: Role of composition and postdeposition annealing

The effects of carbon and postdeposition annealing on white luminescence are studied in amorphous silicon oxycarbide (a-SiCxOy) films grown by chemical vapor deposition. The films showed strong room-temperature luminescence in a broad spectral range from blue-violet to near infrared, depending on excitation energy. Photoluminescence (PL) intensity exhibited good correlation with SiOC bond concentration. At low C (<5%), matrix PL was completely quenched after annealing in O2 even at 500 °C. PL was unaffected by O2 annealing at higher C, and could be enhanced when excited by an ultraviolet laser. These findings are correlated to C- and Si-related O defect centers as luminescence sources in a-SiCxOy.

Comparative study of the effects of thermal treatment on the optical properties of hydrogenated amorphous silicon-oxycarbide

Findings are presented from a systematic study of the effects of postdeposition thermal treatment on the optical characteristics of hydrogenated amorphous silicon-oxycarbide (a-SiCxOyHz) materials. Three different classes of a-SiCxOyHz films: SiC-like (SiC1.08O0.07H0.21), Si-C-O (SiC0.50O1.20H0.22), and SiO2-like (SiC0.20O1.70H0.24), were deposited by thermal chemical vapor deposition. The effects of thermal annealing on the compositional and optical properties of the resulting films were characterized using Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, nuclear reaction analysis, and spectroscopic ultraviolet-visible ellipsometry. As the Si-C-O system evolved from a SiC-like to SiO2-like matrix, its refractive index and optical absorption strength decreased, while its optical band gap increased. Thermal annealing between 500 and 1100 °C resulted in hydrogen desorption from and densification of the a-SiCxOyHz films. Concurrently, thermally induced changes were also observed for...

The origin of white luminescence from silicon oxycarbide thin films

Silicon oxycarbide (SiCxOy) is a promising material for achieving strong room-temperature white luminescence. The present work investigated the mechanisms for light emission in the visible/ultraviolet range (1.5–4.0 eV) from chemical vapor deposited amorphous SiCxOy thin films, using a combination of optical characterizations and electron paramagnetic resonance (EPR) measurements. Photoluminescence (PL) and EPR studies of samples, with and without post-deposition passivation in an oxygen and forming gas (H2 5 at. % and N2 95 at. %) ambient, ruled out typical structural defects in oxides, e.g., Si-related neutral oxygen vacancies or non-bridging oxygen hole centers, as the dominant mechanism for white luminescence from SiCxOy. The observed intense white luminescence (red, green, and blue emission) is believed to arise from the generation of photo-carriers by optical absorption through C-Si-O related electronic transitions, and the recombination of such carriers between bands and/or at band tail states. Thi...

Time-resolved analysis of the white photoluminescence from chemically synthesized SiCxOy thin films and nanowires

The study reported herein presents results on the room-temperature photoluminescence (PL) dynamics of chemically synthesized SiCxOy≤1.6 (0.19 < x < 0.6) thin films and corresponding nanowire (NW) arrays. The PL decay transients of the SiCxOy films/NWs are characterized by fast luminescence decay lifetimes that span in the range of 350–950 ps, as determined from their deconvoluted PL decay spectra and their stretched-exponential recombination behavior. Complementary steady-state PL emission peak position studies for SiCxOy thin films with varying C content showed similar characteristics pertaining to the variation of their emission peak position with respect to the excitation photon energy. A nearly monotonic increase in the PL energy emission peak, before reaching an energy plateau, was observed with increasing excitation energy. This behavior suggests that band-tail states, related to C-Si/Si-O-C bonding, play a prominent role in the recombination of photo-generated carriers in SiCxOy. Furthermore, the P...

Thermal annealing effects on photoluminescence properties of carbon-doped silicon-rich oxide thin films implanted with erbium

Results are presented from the photoluminescence properties of C-doped Si-rich thin film oxides implanted with Er, as investigated for various postdeposition implantation and subsequent annealing and passivation conditions. In particular, it was found that the near-infrared Er luminescence intensity can be increased by up to a factor of ∼4 after a postdeposition anneal at temperatures of 300–1100 °C. The postdeposition annealing also resulted in an enhancement of the green-red (500–600 nm) PL band associated with the film matrix. Post-Er implantation passivation in an oxygen atmosphere resulted in a gradual reduction in intensity for both the Er and matrix PLs, and led eventually to a complete quenching of both PLs at the highest passivation temperature (900 °C). In contrast, hydrogen passivation increased the matrix PL intensity by a factor up to ∼2, but was found to have negligible effects on Er PL intensity over a wide range of passivation temperatures. Analysis of Er and matrix-related PL characterist...

Silicon Oxycarbide Thin films and Nanostructures: Synthesis, Properties and Applications

Silicon oxycarbide (SiCxOy) has been extensively investigated due to its wide use in the Si semiconductor industry in applications that include low-k dielectrics, passivation layers, and etch-stop layers. Furthermore, SiCxOy research has been exploring its prospective use in numerous other technological usages, such as lighting, energy, and biological applications. The latter include white light-emitting materials, hydrogen storage materials, gas sensors, anode materials for lithium batteries, and biomedical devices. SiCxOy materials can intensively luminescence in a broad emission spectral range that spans the ultraviolet, the visible, and even the near-infrared spectrum, when doped with erbium. Herein, we present pertinent results on the material behaviors from chemically synthesized SiCxOy thin films and nanowires. Moreover, their light-emitting properties and underlying mechanisms for light emission are explored in conjunction with data from their thin film counterparts, which are also employed as baseline comparison metric. We further highlight major challenges and promises of such materials.

Strong photoluminescence at 1540 nm from Er-doped amorphous silicon oxycarbide: a novel silicon material for photonic applications

The present investigators have previously reported on strong room-temperature luminescence at 1540 nm from erbium-doped amorphous silicon oxycarbide (a-SiCxOy:Er) thin films. An enhancement of ~20 times was found for asgrown SiC0.5O1.0:Er compared to SiO2:Er control samples under continuous wavelength (cw) pumping at 496.5 nm. Here, we report the effects of post-deposition annealing on the photoluminescence (PL) properties of Er-doped silicon oxycarbide. The amorphous SiCxOy films were grown by thermal chemical vapor deposition (TCVD) at 800°C and postdeposition annealing was conducted in the temperature range 500-1100°C. The thin films were then implanted with 260keV Er ions and subsequently annealed at 900°C. Strong room-temperature photoluminescence around 1540 nm was observed, with efficient Er+3 ion excitation occurring for pumping wavelengths ranging from 460 nm to 600 nm. Modeling of the power dependence of Er luminescence yielded an effective Er excitation cross-section about four orders of magnitude larger than that for a direct optical excitation of Er+3 ions. Additionally, Fourier transform infrared spectroscopy (FTIR) studies of post-deposition annealed samples revealed a strong correlation between the Er PL intensity and the C-O bond concentration in the materials. The work suggests a novel method for achieving efficient Er luminescence in Si-based materials through controlled engineering of the Si-C-O system.

Strong Photoluminescence Enhancement of Silicon Oxycarbide through Defect Engineering

The following study focuses on the photoluminescence (PL) enhancement of chemically synthesized silicon oxycarbide (SiCxOy) thin films and nanowires through defect engineering via post-deposition passivation treatments. SiCxOy materials were deposited via thermal chemical vapor deposition (TCVD), and exhibit strong white light emission at room-temperature. Post-deposition passivation treatments were carried out using oxygen, nitrogen, and forming gas (FG, 5% H2, 95% N2) ambients, modifying the observed white light emission. The observed white luminescence was found to be inversely related to the carbonyl (C=O) bond density present in the films. The peak-to-peak PL was enhanced ~18 and ~17 times for, respectively, the two SiCxOy matrices, oxygen-rich and carbon-rich SiCxOy, via post-deposition passivations. Through a combinational and systematic Fourier transform infrared spectroscopy (FTIR) and PL study, it was revealed that proper tailoring of the passivations reduces the carbonyl bond density by a factor of ~2.2, corresponding to a PL enhancement of ~50 times. Furthermore, the temperature-dependent and temperature-dependent time resolved PL (TDPL and TD-TRPL) behaviors of the nitrogen and forming gas passivated SiCxOy thin films were investigated to acquire further insight into the ramifications of the passivation on the carbonyl/dangling bond density and PL yield.

Intense blue-white luminescence from amorphous silicon oxycarbide (a-SiCxOy) thin films

We report on blue-white luminescence from amorphous silicon oxycarbide a-SiCxOy≤1.68 (0.25<x<0.36) thin films, synthesized by thermal chemical vapor deposition (TCVD) process. The luminescence from SiCxOy was found to exhibit a broad band in the blue-violet to near infrared range (370 - 750 nm), visible to the naked eye in a bright room. The effects of carbon concentration (8.4 at.% < C < 13.6 at.%) in the material and post-deposition annealing treatments (Ar and forming gas 5% of H2 ambient up to 1100°C) on the observed luminescence were studied. The emission intensity slightly decreased with increasing carbon content but was appreciably enhanced in the samples following post-deposition annealing treatment in forming gas 5% of H2 ambient.

A comparative study of a-SiCxOyHz thin films grown via chemical vapor deposition for silicon photonics

We have previously demonstrated strong room-temperature luminescence at 1540 nm from erbium-doped amorphous silicon oxycarbide (a-SiCxOyHz:Er) materials. In this study, pertinent details are presented regarding the role of growth conditions and post-deposition thermal treatment in engineering the structural and optical characteristics of these novel Si-based materials for optimized luminescence performance. Three different classes of a-SiCxOyHz materials were synthesized by thermal chemical vapor deposition, as classified by their carbon and oxygen concentrations: SiC-like; Si-C-O; and SiO2-like. Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, nuclear reaction analysis, and spectroscopic ellipsometry were used to characterize the effects of thermal annealing, as performed at temperatures in the range of 500 - 1100°C, on the structural and optical properties of the resulting films. As the material evolves from the SiC-like, through the Si-C-O, to the SiO2-like matrix, the mass density and refractive index are found to decrease, whereas the optical band gap actually increases. Thermal annealing also resulted in hydrogen desorption from and densification of the a-SiCxOyHz films and in an accompanying decrease in optical gap and an increase in film refractive index. This work suggests that silicon oxycarbide could be a promising Si-based matrix for high-performance Er-doped waveguide amplifiers.