Substrate effect on the electrical properties of a‐Si:H thin films and its modification by diffusion‐blocking interlayers

Electrical dark conductivity (σd) and surface composition of undoped and doped a‐Si:H thin films have been investigated, using coplanar I–V measurements as a function of temperature and Auger electron spectroscopy (AES). The films were prepared by rf glow discharge deposition on standard soda‐lime glass and on alkali‐free glass substrates. Comparing these two sets of substrates for undoped films, we find that σd of the films deposited on soda‐lime glass substrates at room temperature is higher by more than two orders of magnitude, their activation energy is lower by about a factor of 3, and their photosensitivity (σph/σd) is lower by two orders of magnitude than that of the films deposited on alkali‐free glass substrates. We suggest that Na ions, leached from the glass into the a‐Si:H overlayer play a significant role in determining the film conductivity by creating electrically active donorlike states. This conclusion is supported by similar measurements on p‐ and n‐type a‐Si:H films on the same substrat...