Structural Characteristics And Photoelectric Properties Of Large-grained Poly-silicon Films

Large grain poly-silicon thin films have been deposited on quartz substrates by HighFrequency Chemical Vapor Deposition （HFCVD）. The microstructure and optical propertiesof as-deposited films are characterized by scanning electronic microscopy （SEM）, Ramanscattering spectroscopy and ultraviolet and visible spectrophotometer. The electricalproperties of as-doped samples are demonstrated as well by Hall Effect Measurement System.The results show that variations of deposition rate and crystallinity for the poly-silicon filmsare complicated with increasing of the process parameters, including substrate temperature,reaction pressure, SiH₄and B-dopant concentration. Poly-silicon thin film with grain size of2.5μm and band gap of1.55eV has been fabricated at T_s=1000oC, P=200Torr,SiH₄:B₂H₆=1000:8.3. Another result is presented that the changing of B doping would affectdeposition rate and crystallization of the film. Model analysis points out that the increase ofdeposition rate as well as the decline of crystalline volume fraction are due to the promotionof H desorption caused by the B doping which lowers the desorption barrier. Therefore,electrical and optical characteristics of the poly-silicon thin films are largely affected by thechange of B-dopant concentration. Then nc-Si:H/pc-Si heretojunction has been designed byPECVD with the as-deposited poly-silicon thin film as p-type layer. The experiment resultsindicate that I-V characteristic of the heretojunction can be improved evidently by annealingwhich is able to reduce the heretojunction interface defects and lead its short-circuit current（SSC） up to25.2mA.