A Review of the Electrical Characteristics of Metal Contacts on Diamond
Formation of closely spaced selected area ohmic and rectifying contacts on a given semiconductor surface is of fundamental interest for the fabrication of transistor type devices. However, it has been observed that the formation of good ohmic or rectifying contacts is not always easily accomplished on diamond films grown by chemical vapor deposition (CVD). Contacts established with Al or Au on CVD films exhibit highly resistive ohmic or nominally asymmetric behavior, whereas these metals can be used almost routinely to form rectifying contacts on synthetic and natural semiconducting diamond crystals. In the case of CVD grown homoepitaxial films, chemical treatment in hot CrO3 + H2SO4 solution has been reported to allow the fabrication of Au rectifying contacts. Rectifying contacts on CVD grown films of both homoepitaxial and polycrystalline diamond films have been improved by growing an insulating undoped diamond film on a previously deposited B doped semiconducting film. Similar beneficial effects of thin interfacial films of deposited SiO2 on the rectifying characteristics of metal contacts have also been demonstrated. Considerable effort has been directed towards producing low resistivity ohmic contacts on natural semiconducting crystals. A commonly employed technique is the deposition of metals such as Ti, Ta, and Mo and a post-deposition anneal. Specific contact resistances of the order of 10−5 Ω cm2 have been achieved by this technique. Low-resistance contacts have also been obtained by placing metal contacts on highly doped films. The high doping levels can be achieved either by in-situ doping during CVD film growth or by ion implantation at elevated temperatures. © 1991 ELSEVIER B.V.
Das, K; Venkatesan, V; Miyata, K; Dreifus, DL; Glass, JT
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