| Liquid crystal light valve is a kind of high resolution spatial light modulator. However, a single band gap of the photosensitive layer of liquid crystal light valve makes it only on photonic near bandgap energy with high responsivity. Therefore, wide spectrum with graded band gap of the laminated film in the liquid crystal light valve photosensitive layer has a very important research significance, making the wide spectrum of photoelectric detector has become the focus of research scholars.In this work, hydrogenated amorphous / nanocrystalline silicon(a-Si:H/nc-Si:H) thin films, hydrogenated and amorphous silicon-germanium(a-Si Ge:H) films were prepared via radio frequency plasma enhanced chemical vapor deposition(RF-PECVD) with gradient band gap of liquid crystal light valve photosensitive layer as the research background. Nanocrystalline silicon films(nc-Si:H) were also prepared by re-crytsllinzation of amorphous silicon films with high energy electron beam irradiation. The effects of all factors on the microstructure and photoelectric properties of the samples have been investigated by means of AFM, Raman, XRD, FTIR, UV Vis, et al modern characterization method. On the basis of this study, the graded optical band gap photosensitive layer have been designed through the gradient change hydrogen flow rate and flux of germane. The main conclusions of this paper are shown as follows:Electron beam irradiation on amorphous silicon(a-Si:H) thin films. The experimental results show that the electron beam density plays an important role in the crystallinity of the thin films. Analysis of Raman and XRD, the crystallization rate enhanced from 62.9% to 88.9% and the grain size increased from 2.57 nm to 3.60 nm with the increase of the electron beam density, which enhanced the quantum confinement effects producing a widening of the optical energy gap from 1.65 e V to 1.95 e V and the electrical conductivity up to10-4 s·cm-1 for the irradiated films, higher 4 orders of magnitude than as-prepared film and no light induced degradation(S-W effect). Moreover, we found a dramatic decrease of hydrogen content in the deposits from FTIR spectroscopy. The results obtained from AFM images show that all the deposits exhibit a low surface roughness(σRMS≤ 2.5 nm), while surface roughness increased with the increase of electron beam current density.Amorphous / nanocrystalline silicon(a-Si:H/nc-Si:H) thin film prepared by high hydrogen dilution. The experiment shows that with the hydrogen dilution ratio increased from 140/3 to 220/1, the deposition rate of the films decreased. Analysis of Raman, the crystallization rate increased with the increase of the hydrogen dilution ratio, which enhanced the optical energy gap from 1.7e V to 1.92 e V and the dark conductivity from 1.42×10-7 s·cm-1 to 4.19×10-4 s·cm-1, photoconductivity from 7.08×10-6 s·cm-1 to 1.8×10-3 s·cm-1 with the reduced photosensitive. From FTIR spectroscopy analysis, the existence form of H in silicon thin film changes from Si-H2 to Si-H and the ITA/ITO and ILA/ITO ratio of thin films showed a decreasing trend, which showed that the internal order of films were enhanced forming a dense structure.Hydrogenated amorphous silicon-germanium(a-Si Ge:H) thin film. Experimental results indicate that as the increase of the flux of germane, the deposition rate and the surface roughness(RMS) increased from 26.2 to 40.75 nm/min, 1.106 to 3.012 nm, respectively and the morphology of the film becomes worse. The decreased crystallization degree and the increased structure factor R of the films both show the reduced internal order caused by the lattice mismatch between Si and Ge. The optical band gap and the B value of the films decreases with the increase of doping amount, the absorption of the film samples have obvious blue shift. Photosensitive laminated film of ITO-sub/Si1-x Gex/Si1-y Gey/Si1-z Hz/Si1-q Hq can reach 5 orders of magnitude, which can be applied to the photosensitive layer in liquid crystal light valve. |
PDF Full Text Request