Structure in $\frac{d^{2}I}{d{V}^2}$, which corresponds to an increase in conductance at bias voltages equivalent to the surface plasmon energy in GaAs, is observed in $n$-type GaAs-Pb tunnel junctions. Its dependence on the electron concentration of the GaAs electrode has been studied. These data are consistent with the interpretation that the observed structure in $\frac{d^{2}I}{d{V}^2}$ is due to surface plasmon excitation in the GaAs electrode by tunneling electrons.

• Received 13 January 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.293