High Rates and Very Low Temperature Fabrication of Polycrystalline Silicon From Fluorinated Source GAS and Their Transport Properties

Abstract

AbstractLow temperature (50-300°C) growth of polycrystalline silicon (poly-Si) by very high frequency (100MHz) glow-discharge plasma enhanced CVD using SiF4 and H2mixtures was studied. The poly-Si microstructure was strongly affected by the SiF4/H2 gas flow ratio. For example, either (220) or (400) preferentially oriented films were prepared by appropriate SiF4/H2 ratio selection. The addition of small SiH4 flows to the SiF4/H2 mixtures could be used to increase the growth rate while the SiF4/H2 continued to control the film structures such as preferential orientation. Highly crystalline films were grown at a growth rate of 0.52nm/s using SiF4/H2/SiH4 flow rates of 30/90/2.Osccm (respectively). However, at higher SiH4 flows amorphous films were deposited. Under the small SiF4/H2 ratio condition, highly crystallized poly-Si was grown at temperatures as low as 50°C. N/i/Pt Schottky diode solar cells were prepared using these poly-Si for both the n- and the i-layers. These solar cells exhibited good performance; for example, open circuit voltages over 0.32V. N-i-p solar cell results are very promising with 6.2% of conversion efficiency being achieved in the initial trials.