Quantum-confined photoresponse tuning of an Esaki–Tsu-type doping superlattice

Abstract

We performed photocurrent measurements on GaAs-type-A (Esaki–Tsu-type) doping superlattices produced by a δ-doping technique (impurity growth mode) using a new kind of p- and n-contact on a 500 μm × 500 μm mesa plane. We measured, for the first time, a monotonically increased photocurrent below the gap of the host material with horizontal plateaus, as expected for two-dimensional systems. This is the direct confirmation of the two-dimensional nature of this kind of superlattice. In this context, the influence of the contact distance on the photocurrent response is discussed showing that, in contrast to the general case, a variation of the distance between the contacts not only results in a scaling of the photocurrent spectra but changes the complete shape of the photocurrent response for these two-dimensional structures. The possible energetic transitions between the valence band and the conduction band below the gap of the host material, causing the absorption of the doping superlattice, are calculated and explained with an analytical theory. Furthermore, a comparison with other previously performed numerical calculations shows the limits of validity of the analytical calculations presented here.