Effects of the optical energy bandgap and metal work function on the contact resistivity in a-SiGe : H

Abstract

Amorphous silicon based materials, especially a-SiGe : H, have provided a variety of applications in display backplane and sensor materials. The ultimate goal is the development of device architectures that offer improved properties and functionality. In this article, the electrical contact resistivity (ρc) of a-SiGe : H is investigated in terms of the optical energy bandgap modulated by Ge incorporation and the work function of the contact metals. Firstly, the ρc is found to be dependent on the optical bandgap, and this originates from the reduced potential difference between the Fermi level at the metal/a-Si : H interface and the electron mobility edge (Ec), with the decrease in the optical bandgap, which reduces the barrier height. Secondly, the barrier height of the Ti/Cu contact is higher than that of the Mo/Al/Mo contact. In particular, an abundance of Ge atoms is found to have been out-diffused towards the surface and to have formed a mixed interfacial layer, having higher work function than that of the Mo/Al/Mo contact. These results provide evidence that the ρc in a-SiGe : H depends on the work function of the contact layer and is potentially useful for improving device performances.