Plasmon Excitation by Electron Tunneling

In a recent paper, Tsui interprets broad doping-dependent resonances in $\frac{d^{2}I}{d{V}^2}$ for metal contacts on $n$-type GaAs as being caused by the mechanism of inelastic tunneling associated with the excitation of surface plasmons in the GaAs electrode. His interpretation and data are compared with those of Duke, Rice, and Steinrisser. These authors measured the doping of the GaAs by infrared reflectivity. Substantial reductions in the effective value of the density of the dopant found from these measurements (relative to the value quoted by the supplier) require a change in the interpretation of similar resonance structure in $\frac{d^{2}I}{d{V}^2}$ from one in terms of surface plasmons into one in terms of bulk plasmons. Also, the momentum dependence of the electronic self-energy due to the electron-plasmon interaction has the consequence that a barrier-excitation interpretation of the resonance structure is not unique. An interpretation in terms of self-energy effects may be equally satisfactory.