Effect of Ion Doping Conditions on Electrical Conductivity of Amorphous Silicon Films and Its Application to Thin Film Transistors

Abstract

In this paper, we present a systematic study of the effect of phophorus ion doping conditions on electrical properties of amorphous silicon (a-Si) films. A large variation in electrical conductivity for various ion doped amorphous silicon films was found to be related to simultaneous implantation of hydrogen during the P ion doping process. The electrical conductivities of amorphous silicon films were qualitatively related to incorporation of hydrogen during the ion doping process, by measuring optical gaps of ion-doped amorphous silicon films and by simulating the ion doping process. By minimizing hydrogen incorporation during ion doping, a-Si films with conductivity greater than 10^-2 S/cm were obtained, which is at least one order of magnitude higher than the best results in literature for ion doping of plasma-enhanced chemical vapor deposited (PECVD) amorphous silicon films. Reasonably good thin film transistor (TFT) characteristics were obtained for ion doping energy of 10 keV (mobility=0.68 cm² V^-1 s^-1, threshold voltage=3.8 V), which deteriorated upon increase of the ion doping energy.