Investigation On Preparing An Even Large Area And Excellent Optoelectric Properties Hydrogenated Amorphous Silicon Film With Higher Rate

In this dissertation, the main research work was carried out to prepare high stability and excellent optoelectric properties hydrogenated amorphous silicon (a-Si:H) films with higher rate. For this purpose, we did lots of work on equipment improvement, properties analysis and also films preparation technologies. Because of the simplification design of single coil divergent field microwave electron-cyclotron-resonance chemical vapor deposition (MWECR CVD) system, its absorption efficiency of microwave power is not good. We have carefully designed for microwave window, wave-guide coupling and magnetic profile to improve the system properties. Using a dielectric material with different dielectric coefficients in layers as the microwave window which comprised of Al₂O₃ ceramic and BN can match impedance, restrain power reflection, and also improve power absorbability as well as plasma density. As a result that this design, on the one hand, protected microwave system better, on the other hand, it made the microwave transmit efficiently; Using triangle copper plane to couple rectangle wave-guide can make the microwave transmission efficiency reach as high as 92%; Adjusting the magnetic electric current can realize the changes of the magnetic profiles. With the decrease of the electric current, the ECR zone moves up to the window, which is useful to improve the microwave absorption. When the electric current is 115.2A, the microwave absorption efficiency can reach as high as 92.3% in a minute, and as high as 94.6% after 18 minutes later. Meanwhile, We can also change the magnetic profiles in the deposition room by putting a permanent magnet under the substrate. The results showed that, the original divergent magnetic profile turned into a new one, which was divergent firstly and convergent lastly. All these research work mentioned above provides very useful technological information for those researchers using the same deposition system. Magnetic field gradient influences the fabrication of a-Si:H film directly, but work to study the magnetic field profiles quantitatively was not reported yet. In this paper, the way, which obtained quantitatively the magnetic field gradients of three kinds of magnetic field profiles by using Lorentz fitting, was put forwarded. The results indicated that the gradient value of the magnetic field profile nearby the substrate, which was produced by a coil current with 137.7A in the condition of a SmCo permanent magnet was equipped below the substrate holder, is the largest; when the SmCo permanent magnet was taken away, the larger one was produced by the coil current with 137.7A and the smallest one was produced by a coil current with 115.2A. Meanwhile, It was also found that the effect of the magnetic field gradient on the deposition rate of a-Si:H film is very obvious: the larger the magnetic field gradient value is, the higher of the growth rate is. Under the condition of magnetic field profile which was produced by the largest magnetic field gradient mentioned above, the deposition rate of a-Si:H film can reach about 17 /s. Moreover, the effect of the magnetic field gradient on the ununiformity of a-Si:H film is remarkable: the ununiformity of films fabricated in big magnetic field gradient is more obvious. Lastly, the magnetic field gradient also influences the optoelectric properties: a better photosensitivity of a-Si:H film can be obtained at the lower substrate temperature when the magnetic field gradient is high. Therefore this way using Lorentzian fitting to quantitatively obtain magnetic field profiles and magnetic field gradient is applicable for other similar individual deposition system. 0AUsing the IR-data-analysis technology developed by Maley and Langford to determine the hydrogen content of a-Si:H film can better eliminate the error. However, when we calculated the hydrogen content of a-Si:H film deposited by single coil divergent field MWECR CVD system, the results showed there is still a bigger error. In this paper the reason of the error in calculating hydrogen content was investigated. The results indicated that the calculation results of hydrogen content is reliable when the refractive index is close to 3.4 or the fitting thickness is between 0.71μm and 0.89μm in the condition of a small structure factor value in our theoretical deduction and experiment. But because the refractive indexes of the films are not to be controlled easily in the experiment, the thickness should be controlled between 0.710μm -0.89μm in the process of deposition in order to calculate the hydrogen content precisely. Therefore, this work is very important for accurate determination of the hydrogen content in a-Si:H films. In addition, using this technology to analyse the uniformity of a-Si:H films was reported firstly. It the study of fabricating a-Si:H films to realize large-area and uniform deposition, the uneven ECR zone and magnetic field gradient are the primary factors to affect the uniformity of films for the single magnetic field coil MWECR CVD system. Therefore, by improving the rectangle-coupling waveguide and hot-wire-assisted system, and reducing the magnetic field coil current in HW-MWECR CVD system, we deposited the a-Si:H films with thickness uniformity of less than 3.5% above the substrate whose diameter is 6cm. For the measurement, using transmission spectrum technology to calculate the fitting thickness of everyposition on the film we investigated the thickness unevenness, and using transmission spectrum and width of IR absorption peaks technology we studied the structure unevenness. This way to study the structure unevenness of films has not yet been reported. In order to obtain the a-Si:H films with high photoconductivity stability and excellent optoelectric properties, the investigation on fabricating microcrystalline films in the phase transition regime from amorphous to microcrystalline was performed. Firstly, we have deposited the microcrystalline films using by MWECR CVD system. The results showed that low pressure (e.g., below 0.7Pa ) and high substrate temperature(e.g., upon 1700C ) are the important factors to fabricate the microcrystalline silicon in the condition of high microwave power (e.g., 500W ). We have studied the crystalline volume fraction of films by using Raman scattering spectra. It was found that the photosensitivity decreases and the μτproduct increases rapidly when the crystalline volume fraction increase in the films, but when the crystalline volume fraction is ³0%, they have both high stability and excellent optoelectric properties: their photosensitivity is ¹04 and μτproduct is ¹0-5; Secondly, by introducing layer-by-layer (LBL) growth technology and hydrogen plasma treatment on the stacking layers in hot-wire-assisted microwave electron-cyclotron-resonance chemical vapor deposition (HW-MWECR CVD) system, we have fabricated a series of microcrystalline silicon (μc-Si:H) films with different thickness. It was found that when the thickness of films is less than 0.55μm,they have the typical a-Si:H films characteristics whose photoconductivity degrades rapidly. But when the thickness of films is in the range of 0.60μm—0.70μm, they have both characteristics of amorphous and microcrystalline silicon films, in which, the photoconductivity is very sensitive with the thickness changes, but the photoconductivity degradation is very small. For example, for the sample with the thickness of 0.70μm, its photoconductivity degradation rate is ¹1%; When the thickness of films is upon 0.80μm, they have the microcrystalline silicon properties and the photoconductivity degradation rate is only ⁸%. Moreover, it does not change any more by simulating illumination with 53.5 hours. So this LBL technology has important practical value can realize the control for the thickness of microcrystalline silicon films, and deposit the films suiting to fabricate solar cells. In addition, the method we put forwarded using Gaussian fitting to obtain the enough long light-soaking time can be used to study photoconductivity degradation behavior. Thirdly, the hydrogenated nano-amorph silicon films were prepared by using...