Tunneling Characteristics of Al–Al₂O₃–Bi Junctions

Abstract

An elastic tunneling from a metal to a semimetal through an insulating layer is considered. Tunnel current and conductance have been calculated for the case when an energy band of the semimetal along the tunnel direction is non-parabolic, using the WKB approximation. It has been shown that tunnel conductance rises linearly from a voltage corresponding to a band edge and has a peak or a bump at a saddle point. Experimentally, conductance voltage characteristics of Al–Al₂O₃–Bi junctions have been measured at 4.2, 77 and 300°K. Five peaks or bumps are observed at −0.77, −0.16, +0.16, +0.72 and +1.6 volts in the range of −1.2∼+2.2 volts. Energy band models of bismuth are proposed in order to explain an experimental conductance curve and compared with theoretical calculations by Golin and Mase. Current decrease with temperature rise has been observed and is attributed to the temperature dependence of dielectric constant of aluminum oxide.