The Effect of the Amorphous Silicon Alpha-Gamma Transition on Thin Film Transistor Performance

Abstract

ABSTRACTWe have investigated the effect of depositing amorphous silicon (a-Si:H) under α and γ (or dusty) plasma conditions on hydrogen bonding and TFT performance. By infrared measurements three deposition regimes could be identified due to their distinctive absorption curves in the bending mode range of 800 to 900 cm'1. These corresponded to a films deposited below 300°C, γ films deposited below 300°C, and films deposited in either plasma condition at temperatures of 300°C and above. There was a correlation between the a-Si:H material regimes and TFT performance. When the deposition temperature was below 300°C the a-TFTs had a higher field effect mobility than γ-TFTs, but lower stability. For deposition temperatures of 300°C and above the films had more similar properties regardless of whether they were deposited under a or γ conditions. TFT mobilities were the same, but TFTs containing a-Si:H deposited under γ conditions were still more stable. These results show that the mobility and stability of TFTs are optimised for different growth conditions, and that the overall best conditions for TFT manufacture depends upon the specific application.