Microcrystallinity of undoped amorphous silicon films and its effects on the transfer characteristics of thin film transistors

The microcrystallinity of the hydrogenated amorphous silicon films deposited by the usual radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) method and its dependence on the chamber pressure are discussed. Films deposited at the critical pressure posses the highest crystalline volume fraction and the smallest grain size. An ion-bombardment assisted model is proposed to explain the experimental results. Concerning the applications of microcrystalline films to thin film transistors (TFTs), the subthreshold swing and the field effect mobility are also studied.