Improvement of the Electrical Characteristics of a-Si:H TFTs Using the Phosphorus Doping in the Active Layer

This paper suggests a method of phosphorus doping in the active layer to improve the electrical characteristics of hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT). Phosphorus doping in the active layer of a-Si:H was performed by the deposition of a-Si:H through the addition of phosphine gas by plasma enhanced chemical vapor deposition (PECVD). We confirmed that the electrical characteristics of phosphorus doped a-Si:H TFT were improved compared to those of conventional a-Si:H TFT to the extent that the field effect mobility and off current were 0.44 cm2/V•s and 1.53 × 10−12 cm2 when phosphorus was doped by 1 sccm. We investigated the sheet resistance (Rs), root-mean-square roughness (RMS) and density of state (DOS) to demonstrate the improved electrical characteristics. From the results, we confirmed that phosphorus doping in the active layer supplies the electron to use dopant in the channel as well as leads to an improvement of the DOS and higher quality in a-Si:H.