Gold contacts to most III–V and II–VI compounds position the Fermi level at the interface well into the energy gaps of the semiconductors. To position the Fermi level closer to a conduction‐band edge, particularly in the more ionic semiconductors, one may substitute a more electropositive element like Al for the Au contact. To position the Fermi level closer to a valence‐band edge, however, there are no further possibilities among the elemental metals, since Au is the most electronegative of these. Two contact materials, (SN)_x and HgSe, which overcome this limitation have recently been reported. Barriers produced by these contacts on many compound semiconductors will be reported and shown to exhibit the well‐known ionic–covalent transition. Device use and suggestions for further research are mentioned.
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