Properties of Amorphous Silicon Thin Film Transistors with Phosphorous-Doped Hydrogenated Microcrystalline Silicon
AbstractPhosphorous (P) doped hydrogenated microcrystallme silicon (n+μ c-Si:H) films have been prepared by using the hydrogen-diluted plasma enhanced chemical vapor deposition (PECVD) method. The crystallinity of films deposited over the range of SiH4/H2 flow ratios and RF-power is studied by Raman spectroscopy. For a 900 Å thick film deposited at 250°C, a conductivity of 71Ω−1cm−1 and an average crystallinity of 49% is obtained. n+ μ c-Si:H films as well as n+ a-Si:H films are used for both etch stopper and back channel etch type TFTs and the I4-V8 characteristics are compared. For the etch stopper type TFT, the field effect mobility of 0.85 cm2/V.sec, threshold voltages of 2 – 3 V and Ion/Ioff ratio of ∼107 are obtained.