Supermagnetron plasma CVD of highly effective a-CNx:H electron-transport and hole-blocking films suited to Au/a-CNx:H/p-Si photovoltaic cells

Hydrogenated carbon nitride (a-CN_x:H) films (0-500 nm) were deposited on p-Si wafers to make Au/a-CN_x:H/p-Si photovoltaic cells using i-C₄H₁₀/N₂ supermagnetron plasma chemical vapor deposition. At a lower electrode RF power (LORF) of 50 W and an upper electrode RF power (UPRF) of 50-800 W, hard a-CN_x:H films with optical band gaps of 0.7-1.0 eV were formed. At a film thickness of 25 nm (UPRF of 500 W), the open circuit voltage and short circuit current density were 247 mV and 2.62 mA/cm², respectively. The highest energy conversion efficiency was 0.29%. The appearance of the photovoltaic phenomenon was found to be due to the electron-transport and hole-blocking effect of thin a-CN_x:H film.     

Surface etching effects of amorphous C:H and CNx:H films formed by supermagnetron plasma for field emission use

Supermagnetron plasma was used to deposit amorphous hydrogenated carbon (a-C:H) and hydrogenated carbon nitride (a-CN_x:H) films for field-emission devices using i-C₄H₁₀/(H₂ or N₂). It was also used to improve the field-emission characteristics by surface etching using N₂/H₂ plasma. The best emission threshold electric field (E_TH) was 13 and 12 V/μm for devices using as-deposited a-C:H and as-deposited a-CN_x:H films, respectively, while they were remarkably improved to 11 and 8 V/μm by surface etching using N₂/H₂ (120/40 sccm) gas, though surface roughness was slightly increased by the surface etching. The hardness of as-deposited films was higher than 22 GPa.     

Bonding structure and optical properties of a-CNx:H films deposited in CH4-NH3 system

Hydrogenated amorphous carbon nitride (a-CN_x:H) films were deposited by plasma enhanced chemical vapor deposition (PECVD) in CH₄-NH₃ system. The chemical composition and bonding configuration were investigated by XPS and FTIR. The results indicated that both sp²CN and sp³CN bonds generally increased with the increase of the nitrogen concentration, and the N atoms bonded to C atoms through CN, CN and CN bonds. Remarkably, for FTIR spectra, two peaks (2125 and 2200 cm⁻¹) were obviously observed, corresponding to CN bond which was found to predominantly exist in the isonitrile structure. As more nitrogen atoms were incorporated, the optical band gap was found to vary from 1.8 to 2.5 eV. Finally, the conduction mechanisms were discussed at low and high temperature, respectively.     

Optimization of n nc-Si:H and a-SiNx:H layers for their application in nc-Si:H TFT

The n-type doped silicon thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique at high and low H₂ dilutions. High H₂ dilution resulted in n⁺ nanocrystalline silicon films (n⁺ nc-Si:H) with the lower resistivity (ρ ∼0.7 Ω cm) compared to that of doped amorphous silicon films (∼900 Ω cm) grown at low H₂ dilution. The change of the lateral ρ of n⁺ nc-Si:H films was measured by reducing the film thickness via gradual reactive ion etching. The ρ values rise below a critical film thickness, indicating the presence of the disordered and less conductive incubation layer. The 45 nm thick n⁺ nc-Si:H films were deposited in the nc-Si:H thin film transistor (TFT) at different RF powers, and the optimum RF power for the lowest resistivity (∼92 Ω cm) and incubation layer was determined. On the other hand, several deposition parameters of PECVD grown amorphous silicon nitride (a-SiN_x:H) thin films were changed to optimize low leakage current through the TFT gate dielectric. Increase in NH₃/SiH₄ gas flow ratio was found to improve the insulating property and to change the optical/structural characteristics of a-SiN_x:H film. Having lowest leakage currents, two a-SiN_x:H films with NH₃/SiH₄ ratios of ∼19 and ∼28 were used as a gate dielectric in nc-Si:H TFTs. The TFT deposited with the NH₃/SiH₄∼19 ratio showed higher device performance than the TFT containing a-SiN_x:H with the NH₃/SiH₄∼28 ratio. This was correlated with the N−H/Si−H bond concentration ratio optimized for the TFT application.     

Sputter-assisted plasma CVD of polymer-like amorphous CNx:H films using supermagnetron plasma

By using a sputter-assisted chemical vapor deposition (CVD) of supermagnetron plasma, amorphous CN_x:H films were deposited on the lower part of two parallel electrodes. By applying rf power to the upper electrode (UPRF) at 5 W to 800 W, polymer-like a-CN_x:H films were deposited on substrates placed on the lower electrode with an rf power (LORF) of 10 W. The deposition rate increased as UPRF increased. The hardness was as low as about 6.5 GPa, which is less than that of glass (13.1 GPa). The refractive index changed only slightly as UPRF changed from 1.6 to 1.75. The FT-IR spectrum showed strong absorption bands of NH and CH bonds at high and low UPRFs, respectively. The optical band gap was as large as 2.1 to 2.5, and it decreased as UPRF increased. These a-CN_x:H films showed white photoluminescence (PL) with broadband. With the increase of UPRF from 5 W to 800 W, the PL peak energy shifted down from 2.3 eV to 1.9 eV.     

Chemical bonding of a-Ge1−xCx:H films grown by RF reactive sputtering

Amorphous hydrogenated germanium-carbon (a-Ge_1−xC_x:H) films were deposited by RF reactive sputtering pure Ge (1 1 1) target at different flow rate ratios of CH₄/(CH₄+Ar) in a discharge Ar/CH₄, and their composition and chemical bonding were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). XPS and FTIR results showed the content of germanium in the films decreased with the increase of the flow rate ratio CH₄/(Ar+CH₄), and the Ge-C, Ge-H, C-H bonds were formed in the films. The fraction of Ge-C, Ge-H, and C-H bonds was strongly dependent on the flow rate ratio. Raman results indicated that the films also contain both Ge-Ge and C-C bonding. Based on the change of the chemical bonding of a-Ge_1−xC_x:H films with the flow rate ratio CH₄/(CH₄+Ar), an optimal experimental condition for the application of infrared windows was obtained.     

Multilayer amorphous hydrogenated carbon (a-C:H) and SiOx doped a-C:H films for optical applications

In this study SiO_x doped amorphous hydrogenated carbon (a-C:H) films were formed from hexamethyldisiloxane (with hydrogen transport gas) by closed drift ion beam deposition applying variable ion beam energy (300-800 eV). The band gap dependence on the deposition energy was determined and used in production of SiO_x doped a-C:H and a-C:H (formed from acetylene gas) multilayer (two and four layers) stack. Optical properties of the multilayer structures as well as individual layers were analysed in the UV-VIS-NIR range (200-1000 nm). It was shown that employing double or four layer systems, the reflectivity of the multilayer structure-crystalline silicon can be tuned to almost 0% at specific wavelength range (550-950 nm), important in solar cell applications.     

Preparation and time resolution photoluminescence of α-SiCx:H/nc-Si:H multi-layers at room temperature

a-SiC_x:H (amorphous SiC_x:H) and a-Si:H (amorphous Si:H) thin films were deposited under control of the reaction gases SiH₄ + CH₄ and SiH₄ + H₂ by plasma enhanced chemical vapor deposition, respectively. The microstructure of as-deposited a-SiC_x:H and high temperature annealed α-SiC_x:H (6H-SiC_x:H), nc-Si:H (nano-crystal Si:H) thin films were investigated by Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy and ultraviolet-visible spectroscopy. The multi-layer structure of the samples was examined by cross-section transmission electron microscope. The photoluminescence (PL) properties of the samples measured by time-resolved spectroscopy at room temperature showed that the maximum PL intensity and the minimum PL decay time were obtained for the sample annealed at 900 °C. Typical decay times of the samples were determined to be 100 ps and 10 ns by fitting with the use of a bi-exponential function. The latter decay time of our samples closes to the decay time of direct band gap semiconductor, but nearly one thousand times larger than that of porous Si, which was ascribed to the quantum confinement effect.     

Deposition of amorphous carbon nitride films using Ar/N2 supermagnetron sputter

Amorphous carbon nitride (a-CN_x) films were formed by supermagnetron sputter deposition using N₂ and/or Ar gases. Supplying rf power with a substrate-holding electrode (bias sputter) and lowering the gas pressure were found to be effective at decreasing the optical band gap and increasing the hardness. Nitrogen concentrations of bias sputtered films were about 32-35 mass% (30-100 mTorr). The a-CN_x films deposited for electron field emission showed a low-threshold electric field (E_TH). With the decrease of gas pressure, admixture of Ar to N₂ or the use of pure Ar, and the use of bias sputter, the E_TH of a-CN_x films largely decreased to 11 V/μm (30 mTorr Ar/N₂ bias sputter).     

Nanocrystalline silicon films with high conductivity and the application for PIN solar cells

Intrinsic nanocrystalline silicon films (nc-Si:H) were prepared by plasma enhanced chemical vapor deposition (PECVD) method. Films’ microstructures and characteristics were studied with Raman spectroscopy and Atom Force Microscope (AFM). The electronic conductivity of nc-Si:H films was found to be 4.9×10⁰Ω⁻¹ cm⁻¹, which was one order of magnitude higher thanthe reported 10⁻³-10⁻¹ Ω⁻¹ cm⁻¹. And PIN solar cells with nc-Si:H film as intrinsic thin-layer (ITO/n⁺-nc-Si:H/i-nc-Si:H/p-c-Si/Ag) were researched. The cell's performances were measured, the open-circuit voltage V_oc was 534.7 mV, short-circuit current I_sc was 49.24 mA (3 cm²) and fill factor FF was 0.4228.     

Preferred growth of nanocrystalline silicon in boron-doped nc-Si:H Films

Preferred growth of nanocrystalline silicon (nc-Si) was first found in boron-doped hydrogenated nanocrystalline (nc-Si:H) films prepared using plasma-enhanced chemical vapor deposition system. The films were characterized by high-resolution transmission electron microscope, X-ray diffraction (XRD) spectrum and Raman Scattering spectrum. The results showed that the diffraction peaks in XRD spectrum were at 2θ≈47° and the exponent of crystalline plane of nc-Si in the film was (2 2 0). A considerable reason was electric field derived from dc bias made the bonds of Si-Si array according to a certain orient. The size and crystalline volume fraction of nc-Si in boron-doped films were intensively depended on the deposited parameters: diborane (B₂H₆) doping ratio in silane (SiH₄), silane dilution ratio in hydrogen (H₂), rf power density, substrate's temperature and reactive pressure, respectively. But preferred growth of nc-Si in the boron-doped nc-Si:H films cannot be obtained by changing these parameters.     

Evolution of silicon nanoclusters and hydrogen in SiNx:H films: Influence of high hydrostatic pressure under annealing

Hydrogenated silicon-rich nitride (SRN) films of various stoichiometry (SiN_x:H, 0.7 < x ≤ 1.3) were deposited on single-crystalline Si substrates with the use of plasma enhanced chemical vapor deposition at a temperature of 100 °С. Furnace annealing for 5 h in ambient Ar at 1130 °С under atmospheric and enhanced hydrostatic pressure (HP — 11 kbar, 1.1 GPa) was applied to modify the structure of the films. The properties of as-deposited and annealed films were studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence (PL), as well as high-resolution transmittance electron microscopy (HRTEM). According to the Raman data, the as-deposited film, in which the stoichiometry parameter x is below 1.0, contains amorphous silicon nanoclusters. Furnace annealing leads to crystallization of the nanoclusters. From the HRTEM and Raman data, the average size of the Si nanocrystals in the annealed films was 6-7 nm. No silicon nanoclusters were observed in the as-deposited films with relatively low concentration of excessive silicon atoms (the case of SiN_x:H, x > 1); furnace annealing leads to segregation of the Si and Si₃N₄ phases, so, the amorphous Si clusters were observed in annealed films according to Raman data. Surprisingly, after annealing with such high thermal budget, according to the FTIR data, the SRN film with parameter x close to that of the stoichiometric silicon nitride contains hydrogen in the form of SiH bonds. From analysis of the FTIR data of the SiN bond vibrations one can conclude that silicon nitride is partly crystallized in the films with x > 1 after annealing for 5 h. No influence of HP on the structure of Si nanoclusters was observed in the case of SRN films with x ≤ 1.1. Dramatic changes in the PL spectra of the SRN films with the x parameter close to that of the stoichiometric silicon nitride (x ≈ 1.3), annealed under atmospheric pressure and HP, were observed. HP stimulates the formation of very small hydrogenated amorphous nanoclusters. The size of amorphous Si nanoclusters determined from the quantum size effect model describing the PL spectra, should be 2-4 nm in this case.     

Ultraviolet irradiation effect on the properties of leakage current and dielectric breakdown of low-dielectric-constant SiOC(H) films using comb capacitor structure

Low-dielectric constant SiOC(H) films were deposited on p-type Si(100) substrates by plasma-enhanced chemical-vapor deposition (PECVD) using dimethyldimethoxy silane (DMDMS, C₄H₁₂O₂Si) and oxygen gas as precursors. To improve the physicochemical properties of the SiOC(H) films, the deposited SiOC(H) films were exposed to ultraviolet (UV) irradiation in a vacuum. The bonding structure of the SiOC(H) films was investigated by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrical characterization of SiOC(H) films were carried out through I-V measurements using the comb-like patterns of the TiN/Al/Ti/SiOC(H)/TiN/Al/Ti metal-insulator-metal (MIM) structure. Excessive UV treatment adversely affected the SiOC(H) film, which resulted in an increased dielectric constant. Our results provide insight into the UV irradiation of low-k SiOC(H) films.     

PECVD法生长的nc－Si：H膜电导率的研究

使用ＰＥＣＶＤ方法生长了ｎｃ－Ｓｉ：Ｈ膜，Ｘ射线衍射、Ｒａｍａｎ光谱和电镜观测表明样品具备了纳米结构特征。测量了样品在７７Ｋ～４００Ｋ温度范围的电导率，并使用二相随机分布有效介质理论，计算了ｎｃ－Ｓｉ：Ｈ膜中晶粒部分和晶界部分的电导率。对计算结果进行了理论分析，初步探讨了ｎｃ－Ｓｉ结构对其导电性能的影响，提出ｎｃ－Ｓｉ：Ｈ的高电导率来源于膜中纳米晶粒的小尺寸效应。     

Investigation of optical and compositional properties of thin SiNx:H films with an enhanced growth rate by high frequency PECVD method

Hydrogenated thin silicon nitride (SiN_x:H) films were deposited by high frequency plasma enhanced chemical vapor deposition techniques at various NH₃ and SiH₄ gas flow ratios [R = NH₃/(SiH₄ + NH₃)], where the flow rate of NH₃ was varied by keeping the constant flow (150 sccm) of SiH₄. The deposition rate of the films was found to be 7.1, 7.3, 9 and 11 Å/s for the variation of R as 0.5, 0.67, 0.75 and 0.83, respectively. The films were optically and compositionally characterized by reflectance, photoluminescence, infrared absorption and X-ray photoelectron spectroscopy. The films were amorphous in nature and the refractive indices of the films were varied between 2.46 and 1.90 by changing the gas flow ratio during the deposition. The PL peak energy was increased and the linear band tails become broad with the increase in R. The incorporation of nitrogen takes place with the increase in R.     

Deposition of WNxCy thin films for diffusion barrier application using the dimethylhydrazido (2) tungsten complex (CH3CN)Cl4W(NNMe2)

Tungsten nitride carbide (WN_xC_y) thin films were deposited by chemical vapor deposition using the dimethylhydrazido (2⁻) tungsten complex (CH₃CN)Cl₄W(NNMe₂) (1) in benzonitrile with H₂ as a co-reactant in the temperature range 300 to 700 °C. Films were characterized using X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy and four-point probe to determine film crystallinity, composition, atomic bonding, and electrical resistivity, respectively. The lowest temperature at which growth was observed from 1 was 300 °C. For deposition between 300 and 650 °C, AES measurements indicated the presence of W, C, N, and O in the deposited film. The films deposited below 550 °C were amorphous, while those deposited at and above 550 °C were nano-crystalline (average grain size < 70 Å). The films exhibited their lowest resistivity of 840 µΩ-cm for deposition at 300 °C. WN_xC_y films were tested for diffusion barrier quality by sputter coating the film with Cu, annealing the Cu/WN_xC_y/Si stack in vacuum, and performing AES depth profile and XRD measurement to detect evidence of copper diffusion. Films deposited at 350 and 400 °C (50 and 60 nm thickness, respectively) were able to prevent bulk Cu transport after vacuum annealing at 500 °C for 30 min.     

Composite SiOx/fluorocarbon plasma polymer films prepared by r.f. magnetron sputtering of SiO2 and PTFE

Composite films SiO_x/fluorocarbon plasma polymers were prepared by r.f. sputtering from two balanced magnetrons equipped with polytetrafluoroethylene (PTFE) and silica (SiO₂) targets. Argon was used as the working gas. The obtained films were characterised by means of XPS, RBS, FTIR, AFM, TEM, microhardness and static contact angle measurements. The obtained SiO_x/fluorocarbon plasma polymer films reveal different wettability (static contact angle of water ranges from 68° to 40°) and hardness (ranges from 720 to 3200 N/mm²) when the volume fraction ratio (filling factor) of SiO₂ changes from 0.01 to 0.7. The concentration of elements determined by RBS/ERDA varies strongly over this range of filling factors. The heterogeneous structure of the composite films is indicated by TEM at high SiO_x contents.     

Forbidden energy band gap in diluted a-Ge1 − xSix:N films

By means of electron gun evaporation Ge_1 − xSi_x:N thin films, in the entire range 0 ≤ x ≤ 1, were prepared on Si (100) and glass substrates. The initial vacuum reached was 6.6 × 10^− 4 Pa, then a pressure of 2.7 × 10^− 2 Pa of high purity N₂ was introduced into the chamber. The deposition time was 4 min. Crucible-substrate distance was 18 cm. X-ray diffraction patterns indicate that all the films were amorphous (a-Ge_1 − xSi_x:N). The nitrogen concentration was of the order of 1 at% for all the films. From optical absorption spectra data and by using the Tauc method the energy band gap (E_g) was calculated. The Raman spectra only reveal the presence of SiSi, GeGe, and SiGe bonds. Nevertheless, infrared spectra demonstrate the existence of SiN and GeN bonds. The forbidden energy band gap (E_g) as a function of x in the entire range 0 ≤ x ≤ 1 shows two well defined regions: 0 ≤ x ≤ 0.67 and 0.67 ≤ x ≤ 1, due to two different behaviors of the band gap, where for x > 0.67 exists an abruptly change of E_g(x). In this case E_g(x) versus x is different to the variation of E_g in a-Ge_1 − xSi_x and a-Ge_1 − xSi_x:H. This fact can be related to the formation of Ge₃N₄ and GeSi₂N₄ when x ≤ 0.67, and to the formation of Si₃N₄ and GeSi₂N₄ for 0.67 ≤ x.     

The influence of ambient conditions on properties of MgxZn1−xO films by sputtering

The Mg_xZn_1−xO films were prepared in different Ar-O₂ mixture ambience by magnetron sputtering. According to the X-ray diffraction (XRD) patterns and the energy dispersive X-ray spectroscopy (EDS) results, it was found that the Mg contents in the films varied with the different ratios of O₂/O₂+Ar, and the crystal quality of the films improved with the increasing of Mg contents. Meanwhile, the ultraviolet and visible (UV-vis) absorption spectroscopy indicated that the band gap of the films also increased. Moreover, it could be seen that the photoluminescence (PL) spectrum was different from that of undoped Zinc oxide (ZnO) films or the results in other reports on the Mg_xZn_1−xO films: there was no blueshift effect happening for the near-band-edge (NBE) emission in Mg_xZn_1−xO films with different Mg contents.     

Study on variable capacitance diode of (p)nc-Si:H/(n)c-Si heterojunction

Hydrogenated nanocrystalline silicon (nc-Si:H) layers of boron-doped increasing step by step was deposited on n-type crystalline silicon substrate using Plasma Enhanced Chemical Vapor Deposition (PECVD) system. After evaporating Ohm contact electrode on the side of substrate and on the side of nc-Si:H film, a structure of electrode/(p)nc-Si:H/(n)c-Si/electrode was obtained. It is confirmed by electrical measurement such as I-V curve, C-V curve and DLTS that this is a variable capacitance diode.