Properties of the contact on ion cleaned n and p type silicon surfaces

Abstract

Schottky contacts were produced by silver evaporation on Si(100) surfaces cleaned by ion sputtering and partial annealing. The samples work function were measured before and after metal deposition with the Kelvin method, in an experimental set-up which allowed a topografical study and direct comparison between n and p types. Clean surfaces with and without a residual layer of oxide was achieved and controlled by AES. It was found that the Fermi level of all the surfaces was pinned by donor states created by the bombardment and that there was no barrier on n type and an important surface barrier on p type. The diodes we obtained presented no barrier on n type and a rectifying contact on p type. So we deduced that the Schottky barrier is already fully formed before metal contact is achieved. Furthermore study of the electrical properties of the diodes had shown that the bombardment creates donor states responsible for the barrier and a perturbated layer with deep acceptor traps responsible for the current flow mechanism. A residual layer of oxide and a post annealing of the device did not noticeably change the Schottky barrier in the diodes achieved on p type but led to clearly differenciated performances for the diodes achieved on both p and n type substrate. So we therefore concluded that the characteristics of the deep acceptor traps of the superfacial layer are modified by the oxide and annealing, both of which on the other hand having no effect on the surface donor states.