Fabrication Of P-type Amorphous Silicon Thin Films And Poly-Silicom By PECVD

Compared with crystal silicon solar cells and polysilicon solar cells,the silicon-based film solar cells consume less silicon materials and the cost is much lower,especially,the application of low-cost substrates makes it more competitive in cost-control.Presently,amorphous silicon thin film solar cells are popular in the international market.As an important electronic material in energy-information industry,poly-silicon thin films are widely used in LSI and semiconductor discrete devices because of its excellent photoelectric characteristics and Iow-cost of preparation.Poly-silicon thin film solar cells with high efficiency,stability and low-cost would replace the a-Si thin f lm solar cells as a new generation of non-pollution civil solar cells.In this paper,common glass was took as substrate,then boron-doped amorphous silicon films fabricated by using SiH₄/B₂H₆ as gas resource were prepared by plasma enhanced chemical vapor deposition(PECVD)on it.Using the method such as the NKD system,X-Ray Diffraction(XRD),the scanning electron microscope(SEM) system to study different preparation techniques such as radio frequency power,gas doping ratio,substrate temperature's influence to the silicon thin film's microstructure and optical and electricity character,and then propose the explanation for the experiment.It indicated that the deposition rate of amorphous silicon thin films increased linearly with increase of RF power and deposition temperature,respectively. The ratio of boron also affect films growth rate.The film largest growth rate which was 3.3nm/min was reached when it was 1.0%.The absorption coefficient of the amorphous thin films reduced by 10 times after boron doped,when the optical bandgap reduced to about 1.60eV,conductivity changed to the level 10^-3S/cm;Based on this,we doped C into the thin films using SiH₄,B₂H₆ and CH₄ as gas resource, finally got the value about 2.0eV and 10^-5S/cm of the absorption coefficient and conductivity,respectively.By plasma enhanced chemical vapor deposition(PECVD),poly-silicom thin films fabricated by using SiCl₄/H₂ as gas resource were also prepared on the common glass substrate.Using the method such as the NKD system,the scanning electron microscope(SEM)and Raman spectrum system to study different preparation techniques such as radio frequency power,gas doping ratio,reaction pressure, substrate temperature's influence to the poly-silicon thin film's microstructure and optical character.Studying about the poly-silicon thin films shows that the good crystalline fraction could be obtained giving appropriate deposition condition.As to our work system,100W of RF power,35%of SiCl₄ ratio,80Pa of the work pressure could reach higher crystalline fraction,which also increased with the deposition temperature.Additionally,lower gas flux and appropriate proportion of gas to the reaction chamber could improve the crystalline fraction,which became more obvious under the higher RF power.In our experiment condition,80%crystalline fraction, above 200nm grain size,and 7.5nm/min deposition rate could be achieved.The optical character shows that the thin films have the absorption coefficient about 5×10⁴cm^-1and the optical bandgap about 1.5eV,which both reduced with the improvement of crystalline fraction.