Impact of Excited States Transitions on Polarization Property of InAs/InP Quantum Dots

Self-assembled InAs/InGaAsP/InP quantum dots (QD) have been investigated intensively, in which polarization property is a key performance indicator in some photonic devices, such as semiconductor QD optical amplifiers. Conventionally, increased transverse magnetic (TM) polarization is achieved by increased heavy-hole (HH) - light-hole (LH) mixing, such as using closely stacked QDs with
large
stacking layer number (SLN), which was predicted by previous theoretical works and verified experimentally. However, high TM polarization in the closely stacked QDs with
small
SLNs was not predicted by the current theory but confirmed experimentally. In this work, closely stacked InAs/InGaAsP/InP QDs with
small
SLNs are investigated including strain, piezoelectricity and spin-orbit interaction. It is found that the high TM polarization in the closely stacked InAs/InP QDs with
small
SLNs is attributed to strong first excited state transitions and thus more p-type wavefunctions involved, rather than the high HH-LH mixing. With increase of SLN, TM polarization contributed by first excited state transitions decreases, while it contributed by the HH-LH mixing increases.