Optical Modulation of the Refractive Index in Gallium Arsenide Doping Superlattices

Abstract

Doping superlattices, also called nipi superlattices, consist of thin alternating n- and p-doped layers of semiconductor material. This periodic doping profile leads to a periodic electric potential perpendicular to the layers. Potential wells for electrons are in the n-type layers, while potential wells for the holes are in the p-type layers. The periodic potential creates an effective band gap in real space, smaller in energy than the direct gap, which is a function of the density of confined carriers, the impurity doping density, and the thickness of the layers. When mobile electrons and holes are generated, they become spatially separated by the electric potential, screen the oppositely charged ionized dopants in their respective wells, and increase the effective band gap. The resulting tunability of electronic states and optical absorption characteristics as a function of carrier density have been investigated theoretically by Döhler and Ruden.1,2