Bonded Hydrogen Content Research Articles

Influence of intrinsic amorphous silicon passivation layer on the dark-state stability of SHJ cells

Silicon heterojunction (SHJ) solar cells with a two-densities stacked intrinsic hydrogenated amorphous silicon (i-a-Si:H) thin film passivated crystalline silicon surface have high VOC and efficiency. We investigated the dark stability of cells varied with the microstructure of i-a-Si:H layers. It has been found that the dark degradation is mainly from the change in the silicon hydrogen bonded configuration associated with voids size. Furthermore, the less degradation exists on cells with thicker dense i-a-Si:H layers, which results from the high bonded hydrogen content after the enhanced light-soaking (LS) and less change in voids during the dark storage in the i-a-Si:H layers. The microstructure changes, including bonded hydrogen content, voids size, and voids quantity, are related to the initial microstructure of i-a-Si:H layers. This can be illustrated by two actions of non-bonded hydrogens immersed in the undense part of the silicon network. As a result, to enhance the bonded hydrogen content in the i-a-Si:H layers is a preferred method to improve the dark stability of SHJ solar cell after LS.

Towards a Stable and High-Performance Hindered Phenol/Polymer-Based Damping Material Through Structure Optimization and Damping Mechanism Revelation.

Although hindered phenol/polymer-based hybrid damping materials, with excellent damping performance, attract more and more attention, the poor stability of hindered phenol limits the application of such promising materials. To solve this problem, a linear hindered phenol with amorphous state and low polarity was synthesized and related polyurethane-based hybrid materials were prepared in this study. The structure and state of the hindered phenol were confirmed by nuclear magnetic resonance spectrum, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The existence of intermolecular hydrogen bonds (HBs) between hindered phenol and polyurethane was confirmed by FT-IR, and the amorphous state of the hybrids was confirmed by XRD. Moreover, by a combination of molecular dynamics simulation and dynamic mechanical analysis, the relationship between the structure optimization of the hindered phenol and the high damping performance of the hybrids was quantitatively revealed. By constructing the synthetic hindered phenol, the intramolecular HBs between hindered phenols were restricted, while the strength and concentration of the intermolecular HBs increased by increasing the amount of hindered phenol. Thus, intermolecular interactions were enhanced, which lead to the compact chain packing of polyurethane, extended chain packing of hindered phenol, and good dispersion of hindered phenol in polyurethane. Therefore, the stability of the hindered phenol and the damping properties of the hybrids were both improved. The experiment results are expected to provide some useful information for the design and fabrication of high-performance polymeric damping materials.

Investigation of deposition conditions on the structural properties of µc-Si:H

This article is concerned with Raman study of µc-Si:H obtained by PECVD under different deposition conditions. The analysis of crystal fracture and bonded hydrogen content in the layer was carried out. It is shown that as the amorphous phase increases, the content of Si-H bonds prevails. Optimal conditions for deposition of microcrystalline silicon with a low content of hydrogen bonds were defined.

Hydrogen related crystallization in silicon carbide thin films

The present study reports on a detailed investigation on the transition from amorphous to nanocrystalline silicon carbide films grown by means of reactive radiofrequency magnetron sputtering process at low substrate temperatures Ts ranging from 200°C to 500°C. Fourier transform infrared spectroscopy (FTIR), optical transmission measurements and atomic force microscopy (AFM) images were used to study the structural and the optical properties of the films. The results clearly show that hydrogen atoms play a crucial role in the nanocrystal nucleation mechanism. The grown of the films is governed by the interactions between hydrogen atoms and SiC amorphous matrix. The FTIR analysis showed an abrupt structural transition from amorphous a-SiC:H to nc-SiC:H films occurred with increasing Ts from 250°C to 300°C. Upon increasing Ts, the extent of crystallization is substantial and reaches (70±2) % for films deposited at 500°C. In parallel, the total bonded hydrogen content decreases from 30 at.% to less than 6 at.%. The AFM observations confirm the structural changes in the films, and the average grain size reaches a value of about 60nm.

Growth of Hydrogenated Nano-crystalline Silicon (nc-Si:H) Films by Plasma Enhanced Chemical Vapor Deposition (PE-CVD)

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were prepared by home-made PE-CVD systemfromgas mixture of pure SiH4 and H2 at various deposition pressures. Obtained results exhibited that deposition rate increases with increase in deposition pressure. Raman spectroscopy analysis revealed that deposition pressure in PE-CVD is a critical process parameter to induce nanocrystallization in Si:H films. The FTIR spectroscopy analysis results indicate that with increase in deposition pressure hydrogen bonding in films shifts from Si-H to Si-H2 and (Si-H2)n bonded species bonded species. The bonded hydrogen content didn’t show particular trend with optical band gap with change in deposition pressure. The obtained results indicates that 400 mTorr is an optimized deposition pressure of our PE-CVD unit to synthesize nc-Si:H films. At this optimized deposition pressure nc-Si:H films with crystallite size ∼ 5.43 nm having good degree of crystallinity (∼77%) and high band gap (ETauc∼ 1.85 eV) were obtained with a low hydrogen content (4.28 at. %) at moderately high deposition rate (0.75 nm/s). The ease of the present work is to optimize deposition pressure to obtain device quality intrinsicnc-Si:H layer in view of its used in p-i-n solar cells.

Influence of RF power on structural optical and electrical properties of hydrogenated nano-crystalline silicon (nc-Si:H) thin films deposited by PE-CVD

We report synthesis of hydrogenated nanocrystalline silicon (nc-Si:H) thin films by using conventional plasma enhanced chemical vapor deposition (PE-CVD) system from gas mixture of pure silane (SiH4) and hydrogen (H2). We investigated the effect of RF power on structural, optical and electrical properties using various characterization techniques including Raman spectroscopy, FTIR spectroscopy, UV–visible spectroscopy etc. Low angle XRD and Raman spectroscopy analysis revealed that the RF power in PE-CVD is a critical process parameter to induce nanocrystallization in Si:H films. The FTIR spectroscopy analysis results indicate that with increase in RF power the predominant hydrogen bonding in films shifts from Si–H to Si–H2 and (Si–H2)n bonded species bonded species. However, the bonded hydrogen content didn’t show particular trend with change in RF power. The UV–visible spectroscopy analysis shows that the band tail width (E04–ETauc) with increase in RF power. The defect density and Urbach energy also increases with increase in RF power. The highest dark conductivity (and lowest charge carrier activation energy) was obtained for the film deposited at RF power of 125 W indicating that 125 W is optimized RF power of our PE-CVD unit. At this optimized RF power nc-Si:H films with crystallite size ~3.7 nm having good degree of crystallinity (~86.7 %) and high band gap (ETauc ~ 2.01 eV and E04 ~ 2.58 eV) were obtained with a low hydrogen content (6.2 at.%) at moderately high deposition rate (0.24 nm/s).

A Low‐Stress, Elastic, and Improved Hardness Hydrogenated Amorphous Carbon Film

The evolution of hydrogenated amorphous carbon films with fullerene‐like microstructure was investigated with a different proportion of hydrogen supply in deposition. The results showed at hydrogen flow rate of 50 sccm, the deposited films showed a lower compressive stress (lower 48.6%), higher elastic recovery (higher 19.6%, near elastic recovery rate 90%), and higher hardness (higher 7.4%) compared with the films deposited without hydrogen introduction. Structural analysis showed that the films with relatively high sp2 content and low bonded hydrogen content possessed high hardness, elastic recovery rate, and low compressive stress. It was attributed to the curved graphite microstructure, which can form three‐dimensional covalently bonded network.

Effect of Radio-Frequency and Low-Frequency Bias Voltage on the Formation of Amorphous Carbon Films Deposited by Plasma Enhanced Chemical Vapor Deposition

The effect of radio-frequency (RF) or low-frequency (LF) bias voltage on the formation of amorphous hydrogenated carbon (a-C:H) films was studied on silicon substrates with a low methane (CH4) concentration (2–10 vol.%) in CH4+Ar mixtures. The bias substrate was applied either by RF (13.56 MHz) or by LF (150 kHz) power supply. The highest hardness values (∼18–22 GPa) with lower hydrogen content in the films (∼20 at.%) deposited at 10 vol.% CH4, was achieved by using the RF bias. However, the films deposited using the LF bias, under similar RF plasma generation power and CH4 concentration (50 W and 10 vol.%, respectively), displayed lower hardness (∼6–12 GPa) with high hydrogen content (∼40 at.%). The structures analyzed by Fourier Transform Infrared (FTIR) and Raman scattering measurements provide an indication of trans-polyacetylene structure formation. However, its excessive formation in the films deposited by the LF bias method is consistent with its higher bonded hydrogen concentration and low level of hardness, as compared to the film prepared by the RF bias method. It was found that the effect of RF bias on the film structure and properties is stronger than the effect of the low-frequency (LF) bias under identical radio-frequency (RF) powered electrode and identical PECVD (plasma enhanced chemical vapor deposition) system configuration.

Correlation between microstructure and properties of hydrogenated Si thin films grown by plasma enhanced chemical vapor deposition under different hydrogen flow rates

In order to characterize the surface of nanocrystalline hydrogenated silicon (nc-Si:H) and to get more insight into the film’s growth deposited by plasma enhanced chemical vapor deposition (PECVD), spectroscopic ellipsometry measurements have been performed after deposition of profiled layers at different hydrogen flow rate (FH2). This study showed that by increasing the FH2, the layer’s thickness decrease and at the same time the Tauc’s optical band gap remains as high as 1.45eV or much higher. This can be attributed to either the presence of microvoids in the films or an increase in the bonded hydrogen content.

Effect of the defects on the optical and electronic properties of plasma polymerized organic thin films

The microstructure and electronic properties of plasma-polymerized thin films grown by the plasma enhanced chemical vapor deposition (PECVD) method using the cyclohexane as precursor gas are investigated as a function of the radiofrequency power. Infrared, Raman and optical transmission measurements, correlated with electron paramagnetic resonance ones, are applied to characterize the films in their as-deposited state. The results indicate that increasing the radiofrequency power induces a decrease of the total bonded hydrogen content, accompanied by an increase of the carbon C-sp2 hybridization proportion. A decrease of the optical gap, with increasing radiofrequency power also occurs, and might suggest an increasing overlapping of the Gaussian π–π* bands around the Fermi level. Simultaneously, an increase of the spin density is observed in the same range of the radiofrequency power, suggesting that most of the spins originate from C-sp2 complexes.

Analysis of hydrogenated amorphous carbon films deposited by middle frequency pulsed unbalanced magnetron sputtering

Hydrogenated amorphous carbon (a-C:H) films were deposited by middle frequency pulsed unbalanced magnetron sputtering with a mixture gas of argon and methane. The effects of working pressure on the structure, surface morphology, mechanical and optical properties of the a-C:H films were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), Auger electron microscopy (AES), nanoindentation and spectroscopic ellipsometry (SE). It has been found that the film thickness, bonded hydrogen content and RMS surface roughness of a-C:H films increase with increasing working pressure from 0.2 to 1.33Pa, while the sp3 content decreases with the increase of working pressure. AES depth profile exhibits that the C element distributes uniformly across the film thickness, and the transitional layer width between a-C:H film and Si substrate decreases with increasing working pressure. Nanoindentation and spectroscopic ellipsometry measurements indicate that the nanohardness and refractive index of the film decrease with increasing working pressure. IR transmission spectra show that a-C:H film exhibits quite higher transmission in near IR region. The Ge1−xCx/a-C:H multilayer antireflection protective films can effectively improve the transmittance of Ge substrate within the broad band of 2.5–14μm, and a-C:H film can resist rain erosion.

Effects of ion bombardment on microcrystalline silicon growth by inductively coupled plasma assistant magnetron sputtering

Hydrogenated microcrystalline silicon (μc-Si:H) thin films were deposited by inductively coupled plasma assistant magnetron sputtering (ICP-MS) in an Ar-H2 gas mixture. The role of ion bombardment in the growth of μc-Si:H films was studied with increasing negative bias voltages on the substrate holder from 0 to −100 V. Raman scattering, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) were performed to investigate the microstructure changes of deposited Si films. Raman scattering showed that the high energy ion bombardment resulted in crystalline degradation of Si films. The XRD results showed the decrease and even elimination of preferential growth orientation of crystalline Si films with ion bombardment energy increase. The SiH bonding configuration changes and the increase of bonded hydrogen concentration were determined with the analysis of FTIR spectra. Furthermore, the dramatic evolution of cross-sectional morphology of Si thin films was detected by TEM observation.

Hydrogen Dependent Surface Morphology Study of Plasma Deposited SiNx:H Films for Two Gas Systems SiH4/NH3 and SiH4/N2

Partially amorphous silicon nitride thin films were deposited using plasma enhanced chemical vapor deposition technique using the two gas systems: SiH4/NH3 and SiH4/N2. Fourier Transform infrared spectroscopy was employed to derive the relative changes in the bonded hydrogen content with increasing flow rates of NH3 and N2. Surface morphology was monitored using atomic force microscopy. Root mean square surface roughness was found to be dependent on the NH3 and N2 flow rates, unlike silicon nitride films deposited by rf magnetron sputtering with variation in (N2/Ar) (Li et al. Thin Solid Films 334 (1998) 140). The discrepancy has been explained in the light of bonded hydrogen content in these films. The X-ray diffraction technique has also been used to observe the phases of the nitride films which showed the presence of silicon nitride grains oriented in (200), (400) and (221) directions in the predominantly amorphous as-deposited SiN(x):H films.

Design and Synthesis of DLC Films with Different sp<sup>3</sup>/sp<sup>2</sup> Ratios by Middle Frequency Magnetron Sputtering

Diamond-like carbon (DLC) films with different sp3/sp2ratios were deposited using middle frequency magnetron sputtering. The sp3/sp2ratio of the films can be tailored by codoping of Ti and Si elements under different CH4flow rate. The films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The results show that the sp3/sp2ratio ranges from 0.18 to 0.63 with increasing of CH4flow rate. Hydrogen atoms in the films are mainly bonded to sp3carbon atoms. The film deposited at 60 sccm CH4flow rate exhibits the highest bonded hydrogen content.

Spectroscopic ellipsometry studies on hydrogenated amorphous silicon thin films deposited using DC saddle field plasma enhanced chemical vapor deposition system

Hydrogenated amorphous silicon (a-Si H) films deposited on crystalline silicon substrates using the DC saddle field (DCSF) plasma enhanced chemical vapor deposition (PECVD) system have been investigated. We have determined the complex dielectric function, ε(E)=ε1(E)+iε2(E) for hydrogenated amorphous silicon (a-Si:H) thin films by spectroscopic ellipsometry (SE) in the 1.5–4.5eV energy range at room temperature. The results indicate that there is a change in the structure of the a-Si:H films as the thickness is increased above 4nm. This is attributed to either an increase in the bonded hydrogen content and, or a decrease of voids during the growth of a-Si:H films. The film thickness and deposition temperature are two important parameters that lead to both hydrogen content variation and silicon bonding change as well as significant variations in the optical band gap. The influence of substrate temperature during deposition on film and interface properties is also included.

Effect of Hydrogenation on Structural, Optical and Electrical Properties of Amorphous InAsSb Thin Films

Amorphous InAsSb films and hydrogenated InAsSb films are deposited on substrates of quartz glass and silicon by rf magnetron sputtering technique in different gas ambient. The effect of H addition on structure, optical properties and electrical properties of a-InAsSb is studied. It is found that the bonded hydrogen content increases with increasing H2 to Ar flow rate radio(R). When R is 0.1, Hydrogen addition shifts the optical absorption edge to higher energy, decreases the dark conductivity and improves the photo-sensitivity. However, hydrogen addition produces the crystallization of the film at R>0.1. Moreover the optical gap, dark conductivity and photo-sensitivity of the films have a reverse change compared with that in R=0. These results demonstrate that hydrogen has obvious passivation effects on rf sputtered amorphous InAsSb thin films only at R=0.1.

Excimer laser wet oxidation of hydrogenated amorphous silicon

AbstractWe present results of the excimer laser wet oxidisation of submicron thick hydrogenated amorphous silicon films (a‐Si:H) deposited on silicon wafer. The a‐Si:H film irradiation was carried out by multiple‐pulses, large‐spot, 20 ns KrF (248 nm) excimer laser and fluences of 140‐300 mJ/cm2, near to the silicon ablation threshold in an air atmosphere. The oxygen and hydrogen content and bonding in the thin films were analysed by Fourier Transform Infrared Spectroscopy (FTIR) techniques in the range 400‐4000 cm–1. We demonstrate that the presence of water molecules on the silicon surface will increase oxidation by 30‐40%. The bonded hydrogen content in the films after oxidation annealing is decreased from 12 down to around 1 atomic percent. Wet oxidised surfaces present highly hydrophobic properties which appears to be determined by the amorphous silicon structure transformation and silicon surface energy modification forming a silicon/oxide (nitride) interface. (© WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Role of oxygen additive on hydrogen impurity incorporation in nanocrystalline diamond films fabricated by microwave plasma chemical vapor deposition

AbstractIn this work, we study the influence of oxygen additive in the gas phase on hydrogen impurity incorporation into thick nanocrystalline diamond (NCD) films. Various diamond samples were grown on large silicon wafers of 5.08 cm diameter by adjusting the amount of oxygen and nitrogen additives into a conventional CH4/H2 plasma while keeping the other parameters constant using a 5‐kW microwave plasma‐assisted chemical vapor deposition (MPCVD) reactor. The morphology, crystalline quality, and hydrogen impurity content of the produced diamond samples were characterized using scanning electron microscopy, micro‐Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy, respectively. The Raman and the FTIR spectra of the diamond samples indicate that on increasing the amount of oxygen additive in the gas phase, the crystalline quality of the NCD films is significantly enhanced, while their bonded hydrogen content decreases drastically. We conclude that a small amount of oxygen addition has an enhancement effect on the overall quality of diamond films ranging from polycrystalline to nanocrystalline in two ways: improving the diamond crystalline quality and suppressing hydrogen impurity incorporation.

Effects of Hydrogen Partial Pressure on Boron-Doped Hydrogenated Amorphous Silicon (a-Si:H(B)) Properties

Boron-doped hydrogenated amorphous silicon (a-Si:H(B)) thin films have been prepared by DC magnetron sputtering technique under argon and hydrogen mixture. The films were deposited at various hydrogen pressures between 0 and 9 10-5 mbar. The boron concentration estimated from Secondary Ion Mass Spectrometry (SIMS) analysis was found to be around 1.5 1021 cm-3 for all samples. Their physico-chemical, optical and electrical properties are investigated. The physico-chemical properties were studied by infrared absorption measurements. The bonded hydrogen content in the films is then determined using the absorption band of stretching mode. The optical transmission measurements show an increase of the static refractive index and a decrease of optical gap value when hydrogen pressure increases. The dark-conductivity and the photo-conductivity measurements according to the temperature are also reported. We have observed the decreasing of dark-conductivity when hydrogen pressure increases. A slight sensitivity of light was observed for the film deposited at the highest hydrogen pressure. The dark-conductivity was affected by annealing temperature for the whole of the films through its increase in the annealing temperature region 200-350°C.

Comparative study of hydrogenated diamondlike carbon film and hard hydrogenated graphitelike carbon film

The structure, mechanical properties, and friction properties of hydrogenated graphitelike carbon film and typical hydrogenated diamondlike carbon film were investigated comparatively that the hydrogenated graphitelike carbon film has relatively high sp2 content and low bonded hydrogen content and possessed high hardness and elasticity. It was attributed to the curved graphene microstructure, which is able to form three-dimensional covalently bonded network. Furthermore, in comparison with the hydrogenated diamondlike carbon film, the hydrogenated graphitelike carbon film demonstrated excellent friction behavior probably due to the extraordinary structure of hydrogenated graphitelike carbon film.