Effect of anodization time on photoluminescence of porous thin SiC layer grown onto silicon

A porous SiC (PSC) layer was fabricated by anodization of a 1.6 μm thin SiC layer deposited onto p-type Si(1 0 0) substrate by pulsed laser deposition (PLD), using a hot-pressed 6H-SiC(p) as sputtered target. p-Type PSC layers were fabricated by anodization in HF/ethylene glycol electrolyte (1:1 by vol.) at different etching times. The properties of the PSC layer formed by this method were investigated by X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and photoluminescence (PL). The results show, that the growth layer was crystalline and PL spectra exhibit blue band emission centered at 2.95 eV. In addition, the results indicate clearly an increase in PL intensity by ten times of magnitude compared to that exhibited by the unetched sample.     

Relationship between crystal morphology and photoluminescence in polynanocrystalline lead sulfide thin films

Thin films of lead sulfide (PbS) nanoparticles were grown on corning glass and Si(1 0 0) substrates by polyethylene glycol-assisted chemical bath deposition (CBD) method. This paper compares the morphology and the luminescence properties (PL) of the deposited thin films in the presence (or absence) of PEG300 and investigates the effect of deposition temperatures. Surface morphology and photoluminescence properties of samples were analyzed. The PL data show a blue-shift from the normal emission at ∼2900 nm in PbS bulk to ∼360 nm in nanoparticles of PbS thin films. Furthermore, the PL emission of the films obtained without the addition of PEG300 (type 1) was slightly shifted from that of the films obtained in presence of PEG300 (type 2) from ∼360 to ∼470 nm. The blue-shifting of the emission wavelengths from 2900 to ∼360 or 470 nm is attributed to quantum confinement of charge carriers in the restricted volume of nanoparticles, while the shift between the two types of PbS nanoparticles thin films is speculated to be due to an increase in the defect concentration. The blue-shift increased with increase of the deposition temperature, which suggests that there has been a relative depletion in particle sizes during the CBD of the films at higher temperatures. The PbS nanocrystalline thin films obtained in the presence of PEG300 at 60 °C exhibit a high blue luminescence.     

Influence of polyethylene glycol-300 addition on nanostructured lead sulfide thin films properties

The concentration of polyethylene glycol-300 was found to play a crucial role in the formation of nanoparticles in PbS-chemical bath deposition process. We report here an endeavor to set up a relation between the variation of lead sulfide (PbS) nanocrystalline thin film properties, grown by (CBD) process at room temperature on corning glass and Si(100) substrates, with amount fluctuations of polyethylene glycol-300 in the solution. The transmittance of the films, for a fixed reaction time, increased up to ∼ 80% with the increase of % polyethylene glycol-300 in the solution, indicating the formation of very thin films due to the decrease of reaction rate with the increase of the concentration of polyethylene glycol-300. The optical band gaps were found to strongly rely on the composition of the bath deposition and increase with the increase of the polyethylene glycol-300 amount in the solution. Particle sizes between 2.8 and 8.7 nm were obtained by varying the % of polyethylene glycol-300 from 0.2 to 1.5. The concentration of polyethylene glycol-300 not only affects the reaction rate but also the morphology of the obtained films. PbS nanoparticles were found to be oriented preferentially along the < 200> plane. The absorption shifts towards short wavelength indicating a blue-shifting as a consequence of quantum confinement.     

Photoluminescence and photocatalytic properties of Er<Superscript>3+</Superscript>-doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films prepared by sol–gel: application to Rhodamine B degradation under solar light

The effect of Er³⁺ doping (1%) on the structural, optical and photocatalytic properties of In₂O₃ thin films deposited on quartz substrates by spin coating was investigated. The In₂O₃:1% Er³⁺ films, annealed in the temperature range 800–1000 °C, were characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy, UV–Vis spectroscopy, ellipsometry and photoluminescence (PL). The films are polycrystalline with a cubic structure and the lattice parameter increases with the incorporation of Er³⁺ owing to its larger radius. The SEM images of the film show a granular morphology with large grains (~ 200 nm). The doped In₂O₃ film exhibits less transparency than In₂O₃ in the UV–visible region with band gaps of 3.42 and 3.60 eV, respectively. PL shows strong lines at 548 and 567 nm, assigned to Er³⁺ under direct excitation at 532 nm. The energy diagram of the junction In₂O₃:1% Er³⁺/Na₂SO₄ (0.1 M) solution plotted from physical and photoelectrochemical characterizations shows the feasibility of the films for Rhodamine B (RhB) degradation under solar light. The conduction band at 2.22 V deriving from the In³⁺:5s orbital is suitably positioned with respect to the O₂/O ₂ ^· level (~ 1.40 V_SCE), leading to oxidation of 32% of 10 ppm RhB within 40 min of solar irradiation.     

Elaboration and characterization of electrochemically prepared H+-doped polyaniline/Au/a-SiC:H-based chemical sensor

Journal of Solid State Electrochemistry - In this work, we have elaborated and characterized polyaniline (PANI) thin films doped with sulfuric acid (H2SO4) using cyclic voltammetry (CV). The PANI...     

Structural and optical properties of a-Si1−xCx:H films synthesized by dc magnetron sputtering technique

Hydrogenated amorphous SiC films (a-Si_1−xC_x:H) were prepared by dc magnetron sputtering technique on p-type Si(1 0 0) and corning 9075 substrates at low temperature, by using 32 sprigs of silicon carbide (6H-SiC). The deposited a-Si_1−xC_x:H film was realized under a mixture of argon and hydrogen gases. The a-Si_1−xC_x:H films have been investigated by scanning electronic microscopy equipped with an EDS system (SEM-EDS), X-ray diffraction (XRD), secondary ions mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR), UV-vis-IR spectrophotometry, and photoluminescence (PL). XRD results showed that the deposited film was amorphous with a structure as a-Si_0.80C_0.20:H corresponding to 20 at.% carbon. The photoluminescence response of the samples was observed in the visible range at room temperature with two peaks centred at 463 nm (2.68 eV) and 542 nm (2.29 eV). In addition, the dependence of photoluminescence behaviour on film thickness for a certain carbon composition in hydrogenated amorphous SiC films (a-Si_1−xC_x:H) has been investigated.     

Effect of doping on structural,optical and electrical properties of nanostructure ZnO films deposited onto a-Si:H/Si heterojunction

We investigated the structural; optical and electrical properties of ZnO thin films as the n-type semiconductor for silicon a-Si:H/Si heterojunction photodiodes. The ZnO film forms the front contact of the super-strata solar cell and has to exhibit good electrical (high conductivity) and optical (high transmittance) properties. In this paper we focused our attention on the influence of doping on device performance. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along c-axis. SEM images show that all films display a granular, polycrystalline morphology and the ZnO:Al exhibits a better grain uniformity. The transmittance of the doped films was found to be higher when compared to undoped ZnO. A low resistivity of the order of 2.8 × 10⁻⁴ Ω cm is obtained for ZnO:Al using 0.4 M concentration of zinc acetate. The photoluminescence (PL) spectra exhibit a blue band with two peaks centered at 442 nm (2.80 eV) and 490 nm (2.53 eV). It is noted that after doping the ZnO films a shift of the band by 22 nm (0.15 eV) is recorded and a high luminescence occurs when using Al as a dopant. Dark I–V curves of ZnO/a-Si:H/Si structure showed large difference, which means there is a kind of barrier to current flow between ZnO and a-Si:H layer. Doping films was applied and the turn-on voltages are around 0.6 V. Under reverse bias, the current of the ZnO/a-Si:H/Si heterojunction is larger than that of ZnO:Al/a-Si:H/Si. The improvement with ZnO:Al is attributed to a higher number of generated carriers in the nanostructure (due to the higher transmittance and a higher luminescence) that increases the probability of collisions.     

Structural and optical properties of thin films porous amorphous silicon carbide formed by Ag-assisted photochemical etching

In this work, we present the formation of porous layers on hydrogenated amorphous SiC (a-SiC: H) by Ag-assisted photochemical etching using HF/K₂S₂O₈ solution under UV illumination at 254 nm wavelength. The amorphous films a-SiC: H were elaborated by d.c. magnetron sputtering using a hot pressed polycrystalline 6H-SiC target. Because of the high resistivity of the SiC layer, around 1.6 MΩ cm and in order to facilitate the chemical etching, a thin metallic film of high purity silver (Ag) has been deposited under vacuum onto the thin a-SiC: H layer. The etched surface was characterized by scanning electron microscopy, secondary ion mass spectroscopy, infrared spectroscopy and photoluminescence. The results show that the morphology of etched a-SiC: H surface evolves with etching time. For an etching time of 20 min the surface presents a hemispherical crater, indicating that the porous SiC layer is perforated. Photoluminescence characterization of etched a-SiC: H samples for 20 min shows a high and an intense blue PL, whereas it has been shown that the PL decreases for higher etching time. Finally, a dissolution mechanism of the silicon carbide in 1HF/1K₂S₂O₈ solution has been proposed.     

Optical properties of silicon microcolumn grown by nanosecond pulsed laser irradiation

We have investigated the optical properties of silicon pillars formed by cumulative nanosecond pulsed excimer laser irradiation of single-crystal silicon in vacuum created under different repetition rates. The changes in optical characteristics of silicon pillar were systematically determined and compared as the number of KrF laser shots was increased from 1 to 15,000.The results show that silicon pillar PL curves exhibit a blue band around 430 nm and an ultraviolet band peaking at 370 nm with the vanishing of the green emission at 530 nm. A correlation between the intensity of the blue PL band and the intensity of the Si-O absorption bands has been exploited to explain such emission, whereas, the origin of the ultraviolet band may be attributed to different types of defects in silicon oxide.     

Aluminium-induced crystallization of amorphous silicon films deposited by DC magnetron sputtering on glasses

Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550 °C during 4 h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum-annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evidence that crystallization is initiated at 450 °C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450 °C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC).