Properties of amorphous silicon thin film transistors with phosphorous-doped hydrogenated microcrystalline silicon

Phosphorous (P) doped hydrogenated microcrystalline silicon (n(+) mu 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/H-2 flow ratios and RF-power is studied by Raman spectroscopy. For a 900 Angstrom thick film deposited at 250 degrees C, a conductivity of 71 Omega(-1)cm(-1) and an average crystallinity of 49% is obtained. n(+) mu 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 I-d-V-g characteristics are compared. For the etch stopper type TFT, the field effect mobility of 0.85 cm(2)/V.sec, threshold voltages of 2 - 3 V and I-on/I-off ratio of similar to 10(7) are obtained.