Hole Subband Mixing and Polarization of Luminescence from Quantum Dashes: A Simple Model

In this paper, we address the problem of luminescence polarization in the case of nanostructures characterized by an in-plane shape asymmetry. We develop a simple semi-qualitative model revealing the mechanism that accounts for the selective polarization properties of such structures. It shows that they are not a straightforward consequence of the geometry but are related to it via valence subband mixing. Our model allows us to predict the degree of polarization dependence on the in-plane dimensions of investigated structures assuming a predominantly heavy hole character of the valence band states, simplifying the shape of confining potential and neglecting the influence of the out-of-plane dimension. The energy dependence modeling reveals the importance of different excited states in subsequent spectral ranges leading to non-monotonic character of the degree of polarization. The modeling results show good agreement with the experimental data for an ensemble of InAs/InP quantum dashes for a set of realistic parameters with the heavy-light hole states separation being the only adjustable one. All characteristic features are reproduced in the framework of the proposed model and their origin can be well explained and understood. We also make some further predictions about the influence of both the internal characteristics of the nanostructures (e.g. height) and the external conditions (excitation power, temperature) on the overall degree of polarization.