Investigation of the microstructure and optical properties of hydrogenated polymorphous silicon films prepared with pure silane

The dependences of microstructure and optical properties of hydrogenated polymorphous silicon (pm-Si:H) films on total gas pressure were studied. Instead of using high diluted silane in H₂, pure silane was used as the source gas. The films were grown by the radio-frequency plasma-enhanced chemical vapour deposition method. Fourier-transform infrared spectrometry was used to characterize the presence of Si _m H _n clusters in pm-Si:H film deposited on KBr substrate. Atomic force microscopy (AFM) analysis characterized the morphology of the pm-Si:H films and X-ray diffraction at grazing incidence angle (XRDGI) microstructure analysis also confirmed the existence of Si _m H _n nanocrystalline clusters in pm-Si:H. The thickness and optical constants of the films were measured by spectra ellipsometry as well as scanning electron microscopy. Derived using the Tauc relation, the dependence of optical bandgap, E_g , and coefficient, B, on the pressure during deposition process is discussed. The influence of inter-electrode distance on growth rate and surface smooth was analyzed using AFM.     

椭偏透射法测量氢化非晶硅薄膜厚度和光学参数

针对多角度椭偏测量透明基片上薄膜厚度和光学参数时基片背面非相干反射光的影响问题,报道了利用椭偏透射谱测量等离子增强化学气相沉积法(PECVD)制备的a-Si:H薄膜厚度和光学参数的方法,分析了基片温度T_s和辉光放电前气体温度T_g的影响.研究表明,用椭偏透射法测量的a-Si:H薄膜厚度值与扫描电镜(SEM)测得的值相当,推导得到的光学参数与其他研究者得到的结果一致.该方法可用于生长在透明基片上的其他非晶或多晶薄膜. 关键词： 椭偏测量 透射法 光学参数 氢化非晶硅薄膜     

Influence of total gas flow rate on microcrystalline silicon films prepared by VHF-PECVD

Hydrogenated microcrystalline silicon (\mu c-Si:H) films are fabricated by very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) at a silane concentration of 7% and a varying total gas flow rate (Hk₂+SiHk₄). Relations between the total gas flow rate and the electrical and structural properties as well as deposition rate of the films are studied. The results indicate that with the total gas flow rate increasing the photosensitivity and deposition rate increase, but the crystalline volume fraction (Xk_c) and dark conductivity decrease. And the intensity of (220) peak first increases then decreases with the increase of the total gas flow rate. The cause for the changes in the structure and deposition rate of the films with the total gas flow rate is investigated using optical emission spectroscopy (OES).     

Tailored Ceramic Film Growth at Low Temperature by Reactive Sputter Deposition

Reactive sputter deposition of ceramic films with tailored structure is addressed in this article. We begin with a brief overview of reactive sputter deposition specifically related to oxide and nitride films, including techniques for in situ plasma diagnostics. We identify two flux components in the plasma that have a controlling influence on film structure and stoichiometry: (1) the flux bearing sputtered target species, which consists of atoms (M) or reacted molecules (MO_x or MN_x), and (2) the reactive gas flux-containing species in various states of activation. Nonelectronic plasma reactions in which one partner is an excited rare gas species are described, and their role in modifying the sputtered flux, as well as in creating activated reactive gas species, is discussed. We then illustrate the general concepts presented in the overview using four examples of technologically interesting materials grown by rf diode sputter deposition at temperature below 300°C, including: (1) fifth period metal (Zr, Y, Nb) oxides, (2) zirconia-alumina and zirconia-yttria nano-laminates, (3) nanocrystalline aluminum nitride, and (4) vitreous sp² and sp³-bonded boron nitride. Together, these diverse examples form a complementary set that demonstrates the ability to tailor film properties once the chemical and energetic parameters of the deposition process are understood.     

Formation of rippled surface morphology during Si/Si （100） epitaxy by ultrahigh vacuum chemical vapour deposition

The Si epitaxial films are grown on Si (100) substrates using pure Si2H6 as a gas source using ultrahigh vacuum chemical vapour deposition technology. The values of growth temperature T_g are 650 ℃, 700 ℃, 730 ℃, 750 ℃, and 800 ℃. Growth mode changes from island mode to step-flow mode with T_g increasing from 650 ℃ to 700 ℃. Rippled surface morphologies are observed at T_g = 700 ℃, 730 ℃, and 800 ℃, but disappear when T_g = 750 ℃. A model is presented to explain the formation and the disappearance of the ripples by considering the stability of the step-flow growth.     

The influence of gas flow rate on the structural,mechanical, optical and wettability of diamond-like carbon thin films

In this research, diamond-like carbon (DLC) thin films were deposited on silicon substrates by radio-frequency plasma enhanced chemical vapor deposition method using gas mixture of CH₄ and Ar. The effect of different CH₄/Ar gas ratio on the structure, refractive index, transmission and hardness of the DLC thin films were investigated by means of Raman spectroscopy, ellipsometry, Fourier transform Infrared Spectroscopy and nano-indentation methods, respectively. Nuclear resonant reaction analysis was used to measure the amount of hydrogen and carbon in the thin films. Furthermore, wettability of the thin films was achieved by measuring of water contact angle (WCA). The results indicated that the structural properties of the diamond-like carbon thin films are strongly dependent on the composition of gas mixture. Based on ellipsometry results, refractive index of the thin films varied in the range of 1.89–2.06 at 550 nm. FTIR results determined that deposition of DLC thin films on silicon substrate led to an increase of the light transmission in IR region and these films have the potential to be used in silicon optics as the antireflective coatings in this region. Nano-indentation analysis showed that the thin films hardness changed in the range of 7.5–11 GPa. On the other hand hydrogen content and fraction of C?H bonds in the samples increased by an increase in the gas ratio of CH₄/Ar. Also, WCA measurements indicated that WCA for thin films with gas ratio of 3/7 is the most and equal to 79°.     

Surface plasmon resonance response of Au–WO3?x composite films

Surface plasmon resonance of metal–dielectric composite thin films formed by noble metal nanoparticles embedded in a dielectric matrix offers a high degree of flexibility and enables many applications such as surface enhanced spectroscopes, and biological and chemical sensing. In this article, Au–WO_3−x composite films of various Au contents and thicknesses were prepared by the pulsed laser deposition technique, and their SPR responses were measured in the Kreschmann geometry, using a polarized light beam at 640 nm wavelength. Theoretical calculation of SPR responses based on the Bruggeman or Maxwell–Garnett model with the MacLeod general characteristic matrix method is in obvious discrepancy with experimental measurements but it is able to predict the trend in term of the dependence of SPR responses on Au content and thickness of the Au–WO_3−x films. The SPR responses of the Au–WO_3−x films when exposed to NO gas molecules were measured and the preliminary results indicated that gas sensing using the SPR responses of metal–dielectric composite films is feasible.     

Formation of the chemical composition of transition metal dichalcogenide thin films at pulsed laser deposition

The formation of the chemical composition of dichalcogenide films at pulsed laser deposition in vacuum and in rarefied gases (Ar, H₂) is investigated with MoSe _x thin-film coatings. It is found that deposition in gases increases the selenium concentration and somewhat flattens the composition over the substrate surface. To elucidate the mechanisms underlying the MoSe _x film formation, a computer model is used that simulates the motion of a pulsed laser-initiated atomic flux through a rarefied gaseous medium. Using this model, the energy and angular parameters of atomic Mo and Se fluxes toward the substrate are calculated. It is shown that the expansion dynamics of laser plume components (Mo and Se) and the selective sputtering of selenium are the main factors governing the formation of the chemical composition and its distribution over the substrate. The influence of the sort of gas on the efficiency of atomic flux slowdown and scattering and on material losses during deposition is considered.     

Effects of deposition temperature on the structural and morphological properties of thin ZnO films fabricated by pulsed laser deposition

ZnO thin films were grown on Si(1 0 0) substrates using pulsed laser deposition in O₂ gas ambient (10 Pa) and at different substrate temperatures (25, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using XRD, AFM and SEM. At substrate temperature of T=150 °C, a good quality ZnO film was fabricated that exhibits an average grain size of 15.1 nm with an average RMS roughness of 3.4 nm. The refractive index and the thickness of the thin films determined by the ellipsometry data are also presented and discussed.     

Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

Nanocrystalline thin films of TiO₂ were prepared on glass substrates from an aqueous solution of TiCl₃ and NH₄OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO₂ transition from a mixed anatase–rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO₂ thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29–3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors.     

椭圆偏振光谱实时在线监测与离线分析微晶硅薄膜的生长

采用甚高频等离子体增强化学气相沉积技术高速沉积了有无籽晶层两个系列微晶硅薄膜,通过椭圆偏振光谱、拉曼光谱和XRD对薄膜进行了分析,发现采用籽晶层后,在薄膜沉积初期有促进晶化的作用;由于籽晶层减少了薄膜的诱导成核时间,提高了薄膜的沉积速率,对比了实时在线和离线椭圆偏振光谱两种测量状态对分析微晶硅薄膜的影响,研究发现,当薄膜较薄时,实时在线测量得到的薄膜厚度小于离线下的数值;当薄膜较厚时,两种测量条件下得到的薄膜厚度差异较小;实时在线条件下得到的表面粗糙度要大于离线条件下得到的数值,这是由于薄膜暴露在大气中后表面有硅氧化物生成,对表面有平滑作用.     

Strain evolution and morphological transition of magnetron-sputtered CeO2 thin films induced by deposition parameters

Cerium dioxide (CeO₂) films were fabricated on yttria-stabilized zirconia (YSZ) single crystals using unbalanced radio frequency (RF) magnetron sputtering. X-ray diffraction measurements revealed film strain discrepancies under different deposition parameters. Strain evolution was induced by varying sputtering pressure, RF power, and sputtering gas. A distinct morphological transition from a granular surface to an interwoven surface was also realized by varying the above parameters. On the basis of the “atomic peening” mechanism, the influence of different parameters on film strain was discussed. The film surface characteristics were revealed to be highly correlated with film strain. YBa₂Cu₃O_7−δ (YBCO) films were post-deposited on the as-grown CeO₂/YSZ(001) stack by using the trifluoroacetate metal-organic deposition (TFA-MOD) method. The superconducting property of the YBCO layer varied significantly with the morphology of the CeO₂ buffer films.     

Effects of gas composition on the growth of multi-walled carbon nanotube

This paper studies the effects of different gas compositions on the growth of multi-walled carbon nanotube (MWCNT) films by using an electron cyclotron resonance chemical vapor deposition (ECR-CVD) method. The Raman spectrum was employed to explore the composition of the MWCNT films grown under different mixtures of C₃H₈ and H₂. The results showed that the optimum relative intensity ratio of the D band to G band (i.e., I_D/I_G) is 2 for the cases considered in this study. In addition, the morphology and microstructure of the MWCNTs were examined by field emission scanning electron microscopy (FE-SEM) and field emission gun transmission electron microscopy (FEG-TEM). Furthermore, atomic force microscopy (AFM) and scanning thermal microscopy (SThM) were used to study the surface topography and thermal properties of the MWCNTs.     

Film growth and mechanism of LICVD of chromium films from Cr(CO)6 at 248 nm

The probe-beam transmission method was used to study the chemical vapor deposition of chromium films due to photodecomposition of Cr(CO)₆ by pulsed excimer laser radiation at 248 nm in a reversed-substrate configuration, where the film forms on the quartz entrance window of the deposition cell. The dependence of the deposition rate and the film formation time on the laser pulse intensity and repetition rate as well as on the Ar buffer gas pressure was determined for different stages of the deposition process. The experiments were performed at room temperature, on a deposition area of about 0.15 cm², with laser fluences up to 100mJ cm^–2, pulse repetition rates between 5 and 80 pps and buffer gas pressures between 10 and 700 mbar. The results are discussed within the framework of a simple model for LICVD. They reveal the dominant role of gas-phase photodissociation and diffusion in chromium film deposition under the conditions employed. Some results concerning the morphology and the depth distribution of Cr, O, and C in films deposited in the reversed-substrate configuration are also presented.     

Effect of the growth conditions on the structural properties of CuInSe2 thin films obtained by the technique of close spaced vapor transport

Thin films of polycrystalline CuInSe₂ were deposited on Pyrex substrates using a simple system of close spaced vapor transport (CSVT). The used CSVT system is an open horizontal reactor, this does not require vacuum, a gas flow is enough. During the growth phase, the CSVT system is continuously crossed by argon gas. A study on the influence of the source temperature and the deposition duration on the structural properties of the deposited films is reported. Analyses by X-ray diffraction have shown that these films are polycrystalline and have a chalcopyrite structure. The preferential orientation of the (112) plane was obtained for the films deposited at 550 ^°C. From the X-ray spectra we calculated the lattice parameters a and c, the ratio c/a was found to be close to 2. The characterization of the deposited films by an energy dispersion spectrometer (EDS) has shown that their chemical composition is quasistoichiometric with a ratio Cu/In varying from 0.96 to 1.10. Analysis with a scanning electron microscope (SEM) of the deposited films surface has shown that those slightly rich in indium present a more homogeneous morphology and smaller crystallites sizes than the films slightly rich in copper. The measurement of the photoconductivity of the prepared compound has allowed us to determine the value of its gap at room temperature. It was found to be close to 0.99 eV.     

Investigation of porous silicon carbide as a new material for environmental and optoelectronic applications

In this paper, we present an experimental study on the chemical and electrochemical etching of silicon carbide (SiC) in different HF-based solutions and its application in different fields, such as optoelectronics (photodiode) and environment (gas sensors). The thin SiC films have been grown by pulsed laser deposition method. Different oxidant reagents have been explored. It has been shown that the morphology of the surface evolves with the etching conditions (oxidant, concentration, temperature, etc.). A new chemical polishing solution of polycrystalline 6H-SiC based on HF:Na₂O₂ solution has been developed. Moreover, an electrochemical etching method has been carried out to form a porous SiC layer on both polycrystalline and thin SiC films. The PL results show that the porous polycrystalline 6H-SiC and porous thin SiC films exhibited an intense blue luminescence and a green-blue luminescence centred at 2.82 eV (430 nm) and 2.20 eV (560 nm), respectively. Different device structures based on both prepared samples have been investigated as photodiode and gas sensors.     

H2对Ar稀释SiH4等离子体CVD制备多晶硅薄膜的影响

以SiH₄，Ar和H₂为反应气体，采用射频等离子体化学气相沉积方法在300℃下制备了低温多晶Si薄膜.实验发现，反应气体中H₂的比例是影响薄膜结晶质量的重要因素，在适量的H₂比例下制备的多晶Si薄膜具有结晶相体积分数高，氢含量低，生长速率快、抗杂质污染等特性. 关键词： 低温多晶Si薄膜 等离子体CVD 4')" href="#">Ar稀释SiH₄ 2比例')" href="#">H₂比例     

Zinc oxide nanostructured layers for gas sensing applications

Various kinds of zinc oxide (ZnO) nanostructures, such as columns, pencils, hexagonal pyramids, hexagonal hierarchical structures, as well as smooth and rough films, were grown by pulsed laser deposition using KrF and ArF excimer lasers, without use of any catalyst. ZnO films were deposited at substrate temperatures from 500 to 700°C and oxygen background pressures of 1, 5, 50, and 100 Pa. Quite different morphologies of the deposited films were observed using scanning electron microscopy when different laser wavelengths (248 or 193 nm) were used to ablate the bulk ZnO target. Photoluminescence studies were performed at different temperatures (down to 7 K). The gas sensing properties of the different nanostructures were tested against low concentrations of NO₂. The variation in the photoluminescence emission of the films when exposed to NO₂ was used as transduction mechanism to reveal the presence of the gas. The nanostructured films with higher surface-to-volume ratio and higher total surface available for gas adsorption presented higher responses, detecting NO₂ concentrations down to 3 ppm at room temperature.     

Effect of H2 dilution on a-CN:H films deposited by hot-wire chemical vapor deposition

Hydrogenated amorphous carbon nitride (a-CN:H) thin films were deposited by hot-wire chemical vapor deposition (HWCVD) using the gas mixture of CH₄, NH₃ and H₂ precursor gases. The structural and electronic environments studies of H₂ diluted a-CN:H films were carried out by Raman spectroscopy and X-ray photoelectron spectroscopy. The nitrogen content increases while the total carbon contents decreases with increase in H₂ flow rate from 0 sccm to 20 sccm in the a-CN:H films. Moreover, the detail analysis of the carbon core orbital, valence band and hole states of a-CN:H were discussed with different H₂ flow rate.     

Optical characterization of PLD grown nitrogen-doped TiO2 thin films

Nitrogen-doped TiO₂ thin films were prepared by pulsed laser deposition (PLD) by ablating metallic Ti target with pulses of 248 nm wavelength in reactive atmospheres of O₂/N₂ gas mixtures. The layers were characterized by UV-VIS spectrophotometry and variable angle spectroscopic ellipsometry with complementary profilometry for measuring the thickness of the films. Band gap and extinction coefficient values are presented for films deposited at different substrate temperatures and for varied N₂ content of the gas mixture. The shown tendencies are correlated to nitrogen incorporation into the TiO_2-xN_x layers. It is shown that layers of significantly increased visible extinction coefficient with band gap energy as low as 2.89 eV can be obtained. A method is also presented how the spectroscopic ellipsometric data should be evaluated in order to result reliable band gap values.