Hole character and photon polarization switching in quantum dot-in-dots and Quantum Dot Molecules

Three-dimensional (3D) quantum confinement in semiconductor quantum dots (QDs) implies valence band mixing, which in turns determines the polarization properties of the emitted photons. However, the valence band structure in QDs has been investigated so far mostly in self-assembled strained dots, in which heavy- and light-hole mixing is weak and the confinement geometry is fixed to a large extent. Here we propose novel schemes for engineering and switching the hole-character and the polarization of the emitted photons in pyramidal QD heterostructures. Valence-band engineering and deterministic control of the hole-character in quantum nanostructures self-formed in inverted pyramids have been reported, both for GaAs/AlGaAs Dot-in-Dot (DiDs) [1] and for AlGaAs Quantum-Dot Molecules (QDMs) [2]. Side-view polarization-resolved photoluminescence spectra clearly demonstrated the switching of the ground state character from light-hole (LH) to heavy-hole (HH) as the geometrical configuration is changed [1]. Here, we propose and theoretically demonstrate dynamic switching of hole-character and polarization induced by applying an electric field on pyramidal DiDs and QDMs (Figs. 1 and 2). Our studies show that it is possible to separately confine the electron state and the hole states such that the holes are confined in thinner low-potential regions, and are hence predominantly of heavy hole character. The electric fields required for such switching are calculated for a variety of DiD and QDM configurations, showing that realistic values of less than 105 V/cm are sufficient for inducing the switching. The fabrication of such structures will be discussed. Such dynamic switching of photon polarization is interesting for various QD emitters such as lasers and single photon sources.