Semi-quantitative study on the Staebler-Wronski effect of hydrogenated amorphous silicon films prepared with HW-ECR-CVD system

The method of numerical simulation is used to fit the relationship between the photoconductivity in films and the illumination time. The generation and process rule of kinds of different charged defect states during illumination are revealed. It is found surprisingly that the initial photoconductivity determines directly the total account of photoconductivity degradation of sample.

Study on stability of hydrogenated amorphous silicon films

Hydrogenated amorphous silicon （a-Si：H） films with high and same order of magnitude photosensitivity （-10^5） but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content （CH） as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si：H films. We used hydrogen elimination model to explain our experimental results.

Research on the optimum hydrogenated silicon thin films for application in solar cells

Hydrogenated silicon （Si：H） thin films for application in solar ceils were deposited by using very high frequency plasma enhanced chemical vapour deposition （VHF PECVD） at a substrate temperature of about 170 ℃, The electrical, structural, and optical properties of the films were investigated. The deposited films were then applied as i-layers for p-i-n single junction solar cells. The current-voltage （I - V） characteristics of the cells were measured before and after the light soaking. The results suggest that the films deposited near the transition region have an optimum properties for application in solar cells. The cell with an i-layer prepared near the transition region shows the best stable performance.

Smooth Surface Morphology of Hydrogenated Amorphous Silicon Film Prepared by Plasma Enhanced Chemical Vapor Deposition

Influence of the parameters of plasma enhanced chemical vapor deposition （PECVD） on the surface morphology of hydrogenated amorphous silicon （α-Si：H） film was investigated. The root-mean-square （RMS） roughness of the film was measured by atomic force microscope （AFM） and the relevant results were analyzed using the surface smoothing mechanism of film deposition. It is shown that an α-Si：H film with smooth surface morphology can be obtained by increasing the PH3/N2 gas flow rate for 10% in a high frequency （HF） mode. For high power, however, the surface morphology of the film will deteriorate when the Sill4 gas flow rate increases. Furthermore, optimized parameters of PECVD for growing the film with smooth surface were obtained to be Sill4：25 sccm （standard cubic centimeters per minute）, At： 275 sccm, 10%PH3/N2：2 sccm, HF power： 15 W, pressure： 0.9 Torr and temperature： 350℃. In addition, for in thick fihn deposition on silicon substrate, a N20 and NH3 preprocessing method is proposed to suppress the formation of gas bubbles.

Charge storage characteristics of hydrogenated nanocrystalline silicon film prepared by rapid thermal annealing

The early stages of hydrogenated nanocrystalline silicon （nc-Si：H） films deposited by plasma-enhanced chemical vapour deposition were characterized by atomic force microscopy. To increase the density of nanocrystals in the nc-Si：H films, the films were annealed by rapid thermal annealing （RTA） at different temperatures and then analysed by Raman spectroscopy. It was found that the recrystallization process of the film was optimal at around 1000℃. The effects of different RTA conditions on charge storage were characterized by capacitance-voltage measurement. Experimental results show that nc-Si：H films obtained by RTA have good charge storage characteristics for nonvolatile memory.

The role of hydrogen in hydrogenated microcrystalline silicon film and in deposition process with VHF-PECVD technique

The role of hydrogen in hydrogenated microcrystalline silicon （μc-Si：H） thin films in deposition processes with very high frequency plasma-enhanced chemical vapour deposition （VHF-PECVD） technique have been investigated in this paper. With in situ optical emission spectroscopy （OES） diagnosis during the fabrication of μc-Si：H thin films under different plasma excitation frequency Ve （60MHz-90MHz）, the characteristic peak intensities （IsiH＊, IHα＊ and IHβ＊ ） in SiH4＋H2 plasma and the ratio of （IHα＊ ＋ IHβ＊ ） to IsiH＊ were measured; all the characteristic peak intensities and the ratio （IHα＊ ＋ IHβ＊ ）/IsiH＊ are increased with plasma excitation frequency. It is identified that high plasma excitation frequency is favourable to promote the decomposition of SiH4＋H2 to produce atomic hydrogen and SiHx radicals. The influences of atomic hydrogen on structural properties and that of SiHx radicals on deposition rate of μc-Si：H thin films have been studied through Raman spectra and thickness measurements, respectively. It can be concluded that both the crystalline volume fraction and deposition rate are enhanced with the increase of plasma excitation frequency, which is in good accord with the OES results. By means of FTIR measurements, hydrogen contents of μc-Si：H thin films deposited at different plasma excitation frequency have been evaluated from the integrated intensity of wagging mode near 640 cm^-1. The hydrogen contents vary from 4% to 5%, which are much lower than those of μc-Si：H films deposited with RF-PECVD technique. This implies that μc-Si：H thin films deposited with VHF-PECVD technique usually have good stability under light-soaking.

Characterization of doped hydrogenated nanocrystalline silicon films prepared by plasma enhanced chemical vapour deposition

The B- and P-doped hydrogenated nanocrystalline silicon films （nc-Si：H） are prepared by plasma-enhanced chemical vapour deposition （PECVD）. The microstructures of doped nc-Si＇H films are carefully and systematically characterized by using high resolution electron microscopy （HREM）, Raman scattering, x-ray diffraction （XRD）, Auger electron spectroscopy （AES）, and resonant nucleus reaction （RNR）. The results show that as the doping concentration of PH3 increases, the average grain size （d） tends to decrease and the crystalline volume percentage （Xc） increases simultaneously. For the B-doped samples, as the doping concentration of B2H6 increases, no obvious change in the value of d is observed, but the value of Xc is found to decrease. This is especially apparent in the case of heavy B2H6 doped samples, where the films change from nanocrystalline to amorphous.

Room Temperature Growth of Hydrogenated Amorphous Silicon Films by Dielectric Barrier Discharge Enhanced CVD

Hydrogenated amorphous silicon （a-Si： H） films were deposited on Si （100） and glass substrates by dielectric barrier discharge enhanced chemical vapour deposition （DBD-CVD） in （SiH4＋H2） atmosphere at room temperature. Results of the thickness measurement, SEM （scanning electron microscope）, Raman, and FTIR （Fourier transform infrared spectroscopy） show that with the increase in the applied peak voltage, the deposition rate and network order of the films increase, and the hydrogen bonding configurations mainly in di-hydrogen （Si-H2） and poly hydrogen （SiH2）n are introduced into the films. The UV-visible transmission spectra show that with the decrease in SiH4/ （SiHn＋H2） the thin films＇ band gap shifts from 1.92 eV to 2.17 eV. These experimental results are in agreement with the theoretic analysis of the DBD discharge. The deposition of a-Si： H films by the DBD-CVD method as reported here for the first time is attractive because it allows fast deposition of a-Si： H films on large-area low-melting-point substrates and requires only a low cost of production without additional heating or pumping equipment.

SUBSTRATE EFFECT ON HYDROGENATED MICROCRYSTALLINE SILICON FILMS DEPOSITED WITH VHF-PECVD TECHNIQUE

Raman spectra and scanning electron microscope （SEM） techniques were used to determine the structural properties of microcrb＇stalline silicon （μc-Si：H） films deposited on different substrates with the very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD） technique. Using the Raman spectra, the values of crystalline volume fraction Xc and average grain size d are 86%, 12.3nm; 65%, 5.45nm; and 38%, 4.05nm, for single crystalline silicon wafer, coming 7059 glass, and general optical glass substrates, respectively. The SEM images further demonstrate the substrate effect on the film surface roughness. For the single crystalline silicon wafer and Coming 7059 glass, the surfaces of the μc-Si：H films are fairly smooth because of the homogenous growth or h＇ttle lattice mismatch. But for general optical glass, the surface of the μ-Si： H film is very rough, thus the growing surface roughness affects the crystallization process and determines the average grain size of the deposited material. Moreover, with the measurements of thickness, photo and dark conductivity, photosensitivity and activation energy, the substrate effect on the deposition rate, optical and electrical properties of the μc-Si：H thin films have also been investigated. On the basis of the above results, it can be concluded that the substrates affect the initial growing layers acting as a seed for the formation of a crystalline-like material and then the deposition rates, optical and electrical properties are also strongly influenced, hence, deposition parameter optimization is the key method that can be used to obtain a good initial growing layer, to realize the deposition of μc-Si：H films with device-grade quality on cheap substrates such as general glass.

Light induced microstructure transformation in a-Si：H films

A series of a-Si：H films are deposited by hot wire assisted microwave electron cyclotron resonant chemical vapour deposition （HW-MWECR-CVD）, subsequently exposed under simulated illumination for three hours. This paper studies the microstructure change during illumination by Fourier Transformation Infrared （FTIR） spectra. There are two typical transformation tendencies of microstructure after illumination. It proposes a model of light induced structural change based on the experimental results. It is found that all samples follow the same mechanism during illumination, and intrinsic structure of samples affect the total H content.

Modification of ADP extinguishing powder by siliconization in spray drying

Superfine spherical fire-extinguishing powder, ammonium dihydrogen phosphate （ADP, NH4 H2 PO4）, was prepared by spray drying and modified in situ with methyl hydrogen silicone oil （MHSO） emulsion and the fluorinated surfactant FK-510. The influences of the MHSO mass ratio on the hydrophobicity, sur- face composition, surface morphology, dispersion and particle-size distribution of the NH4H2PO4 were studied, and the influence of the drying air temperature on the decomposition of the NH4H2PO4 was also researched. The results indicate that the MHSO and FK-510 congregate on the particle surfaces and then form a hydrophobic shell. This shell improves the particle hydrophobicity and leads to a fine dispersion of the particles. During the process of preparing the precursor solution, 3 wt% （based on the weight of NH4H2 PO4 ） was chosen as the optimum value of the MHSO mass ratio. During the spray drying, a low abso- lute humidity of the air should be maintained, and it is very important to keep the exit-air temperature below 100℃ to avoid decomposition.

Effects of seed layer on the performance of microcrystalline silicon germanium solar cells

Using plasma enhanced chemical vapor deposition（PECVD） at 13.56 MHz,a seed layer is fabricated at the initial growth stage of the hydrogenated microcrystalline silicon germanium(μc-Si1-xGex:H) i-layer.The effects of seeding processes on the growth ofμc-Si1-xGex:H i-layers and the performance ofμc-Si1-xGex:H p-i-n single junction solar cells are investigated.By applying this seeding method,theμc-Si1-xGex:H solar cell shows a significant improvement in short circuit current density(Jsc) and fill factor（FF） with an acceptable performance of blue response as aμc-Si:H solar cell even when the Ge content x increases up to 0.3.Finally,an improved efficiency of 7.05%is achieved for theμc-Si0.7Ge0.3:H solar cell.

Analysis of the p^+/p window layer of thin film solar cells by simulation

The application of a p~＋/p configuration in the window layer of hydrogenated amorphous silicon thin film solar cells is simulated and analyzed utilizing an AMPS-ID program.The differences between p~＋-p-i-n configuration solar cells and p-i-n configuration solar cells are pointed out.The effects of dopant concentration, thickness of p~＋-layer,contact barrier height and defect density on solar cells are analyzed.Our results indicate that solar cells with a p~＋-p-i-n configuration have a better performance.The open circuit voltage and short circuit current were improved by increasing the dopant concentration of the p~＋ layer and lowering the front contact barrier height.The defect density at the p/i interface which exceeds two orders of magnitude in the intrinsic layer will deteriorate the cell property.