| The fabrication method and application of Poly-silicon are reviewed. The research progress of metal-induced crystallization of amorphous silicon, the mechanism and the application of Al-induced crystallization of amorphous silicon are summarized in detail in this thesis.In this work, a one-chamber deposition apparatus, which contributes two deposition system of both Thermal Evaporation Deposition and Plasma Enhanced Chemical Vapor Deposition (PECVD), was specially designed. Al/a-Si:H bilayer and a-Si:H/Al/a-Si:H trilayer thin films were deposited successfully by thermal evaporation and PECVD in the one chamber apparatus. The effect of different parameters, such as the thickness of Al sublayer, annealing temperature and heat treatment time, on both the formation of crystalline silicon and the mechanism of Al-induced crystallization of hydrogenated amorphous silicon(a-Si:H) in Al/a-Si:H bilayer and a-Si:H/Al/a-Si:H trilayer thin films at low temperature were studied through the techniques of XRD, Raman, XPS, SEM, TEM, HRTEM and SIMS etc.The results show that crystalline silicon is formed at low temperature of 250癈 at most in Al/a-Si:H thin films. C-Si phase forms rapidly at the initial stage of heat treatment and then increases slowly and smoothly with the development of heat treatment. The amount of crystalline Si, following with a consumption of c-Al from Al sublayer, increases with the increase in both the thickness of Al sublayer and the annealing temperature.It is proposed that the mechanism of Al-induced crystallization of a-Si:H at low temperature are summarized, because of many large density of, when contacts with, The intermixed layer of (Al)-(a-Si:H), in whichhigh concentration of Al atoms occurred, is formed at the interface between a-Si:H and Al layers. The multiphase diffusion takes place easily through aluminum/silicon intermixed layer due to a lot of defects, dangling bonds, voids and micro pores existed in the interface of a-Si:H film. Because of the Al atoms planted in a-Si:H matrix, which have different electronegative with Si atoms, the chemical bond of Si-Si is more active than that in a system without disturbing. Therefore the Si-Si bond is going to be rearranged, promoting the nucleation of silicon, while the film is annealed at 250癈 or above. Crystalline silicon formed in the film is increased with increasing both annealing time and annealing temperature. At the same time, with inducing the crystallization of amorphous silicon, two kinds of Al atoms, diffused through the interface of new-formed crystalline silicon phases from the Al sublayer as well as intermixed layer to the growth surface of the film.That the diffusion of Al atoms in Al/a-Si:H composite films is attribute to Pick's second law, the expression of Al concentration as function of annealing time "t" at the "x" depth from the Al sublayer to the cap layer of a-Si:H is shown as follows.where the diffusion coefficient of Al atoms in a-Si:H is about 1.08xl(rMmV.Two kinds of Si2P binding energy peaks of both amorphous silicon and crystalline silicon at 98.66eV and 99.23eV, respectively, were found in Al/a-Si:H composite films annealed. The intensity of Si2p binding energy of crystalline silicon is increased with the increase in thickness of the Al sublayer, and the Siip binding energy of the amorphous silicon shift to high value with increasing thickness of the Al sublayer.The mobility and conductivity of Al-a-Si:H composite films were also obtained. The results show that the mobility of composite film is as big as3.85cm2/V.s after crystallization. The conductivity increases exponentially with the increase in thickness of the Al sublayer., and the relationship between the conductivity cr and the volume content of crystalline silicon P in the Al/a-Si.H composite film is shown as:It is observed that the columnar microstructure is dependent on crystalline silicon induced by Al atoms in Al/a-Si:H bilayer films. The super lattice structure with 9.18A crystal lattice space is observed in the cross-s...
|
PDF Full Text Request