Spyros Gallis

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...

Efficient energy transfer from silicon oxycarbide matrix to Er ions via indirect excitation mechanisms

Efficient Er excitation was observed in Er-doped silicon oxycarbide with strong room-temperature photoluminescence of ∼1540nm within a broad (460–600nm) band. Er PL power dependence modeling yielded an effective Er excitation cross section of approximately four orders of magnitude higher than direct Er excitation. PL for undoped a-SiC0.5O1.0 extended from visible to near infrared (500–750nm), with intensity decreasing with Er doping. Er photoluminescence excitation overlapped with the Urbach edge in a-SiC0.5O1.0:Er absorption spectrum. Energy transfer from electron-hole recombination at band edges or/and defect levels in a-SiC0.5O1.0:Er may provide an efficient excitation route for Er ions via electron excitation from ground state (I15∕24) to 4f levels.

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...

Photoluminescence in erbium doped amorphous silicon oxycarbide thin films

Photoluminescence (PL) in Er-doped amorphous silicon oxycarbide (a-SiCxOy:Er) thin films, synthesized via thermal chemical vapor deposition, was investigated for carbon and oxygen concentrations in the range of 0–1.63. Intense room-temperature PL was observed at 1540 nm, with the PL intensity being dependent on the carbon and oxygen content. The strongest PL intensity was detected for a-SiC0.53O0.99:Er when pumped at 496.5 nm, with ∼20 times intensity enhancement as compared to a-SiO2:Er. Broadband excitation in the visible was observed for a-SiC0.53O0.99:Er. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses suggest that the formation of Si–C–O networks plays an important role in enhancing the Er optical activity in a-SiCxOy:Er films.

Optical and structural characterization of thermal oxidation effects of erbium thin films deposited by electron beam on silicon

Thermal oxidation effects on the structural, compositional, and optical properties of erbium films deposited on silicon via electron beam evaporation were analyzed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and spectroscopic ellipsometry. A gradual rise in oxidation temperature from 700 to 900 °C resulted in a transition from ErO- to Er2O3-rich phase. Additional increase in oxidation temperature above 1000°C led to the formation of erbium silicate due to further oxygen incorporation, as well as silicon out-diffusion from the substrate. A silicon oxide interfacial layer was also detected, with its thickness increasing with higher oxidation temperature. Additionally, film refractive index decreased, while its Tauc bandgap value increased from ∼5.2 eV to ∼6.4 eV, as the oxidation temperature was raised from 700 °C to above 900 °C. These transformations were accompanied by the appearance of an intense and broad absorption band below the optical gap. Thermal oxidation ...

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.