Tunable infrared photoemission sensor on Si using epitaxial ErSi 2/Si heterostructures

Abstract

We study the internal photoemission response of an Ir/Si/ErSi 2 asymmetrical metal-silicon-metal heterostructure, or “tunable infrared photoemission sensor” (TIPS). The TIPS photoresponse results from the combination of both hole and electron photoemission, from one metallic film to the other, above or below the trapezoidal barrier formed by the epitaxial Si layer. Due to the asymmetry of the potential barrier, the effective barrier heights (EBHs) can be modulated by an external bias applied between the two metallic electrodes. This leads to a large dependence of the TIPS photoresponse on the applied bias. The experimental TIPS cutoff wavelength is shifted from around 1.4 μm to more than 6 μm with quantum efficiencies varying from 2.5% at 3 μm to 8.5% at around 1 μm when a positive bias of a few hundred meV is applied to the Ir electrode. The photoresponse of such a heterostructure is quantitatively fitted using the Fowler photoemission formalism, taking into account: (a) the respective absorption in each metallic film and (b) the four different photoemission processes. These fits allow the determination of the EBHs as a function of the applied bias and show that in an asymmetric heterostructure hot carriers, both holes and electrons, can cross a 200 nm thick epitaxial Si layer.