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

J. Bregman, J. Gordon, Yoram Shapira, Elvira Fortunato, Rodrigo Martins, Leopoldo Guimaraes

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Abstract

Electrical dark conductivity (σd) and surface composition of undoped and doped a-Si:H thin films have been investigated, using coplanar I−V 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 (σphd) 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 substrates and by AES results. Films of a-Si:H, grown on thin a-Si:C:H interlayers on soda-lime glass, showed very low Na concentrations and low dark conductivities as found by AES and electrical measurements, respectively. The role of the a-Si:C:H interlayers as diffusion barriers is discussed.

Original languageEnglish
Pages (from-to)2628-2631
Number of pages4
JournalJournal of Vacuum Science and Technology A: Vacuum, Surfaces and Films
Volume7
Issue number4
DOIs
Publication statusPublished - Jul 1989

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