Intersubband-surface-plasmon-polaritons in all-semiconductor planar plasmonic resonators

The strong coupling between a collective intersubband excitation in a multiple quantum well (MQW) structure and the ground photonic mode of the semiconductor microcavity (MC) leads to formation of coherent mixed modes termed... [ view full abstract ]

The strong coupling between a collective intersubband excitation in a multiple quantum well (MQW) structure and the ground photonic mode of the semiconductor microcavity (MC) leads to formation of coherent mixed modes termed intersubband-cavity-polaritons. The intersubband-cavity-polaritons have attracted great attention of the research community. It is mainly due to the fact that intersubband optoelectronic devices operating in a strong coupling regime have potential for applications. The majority of work on the intersubband-cavity-polaritons has explored all dielectric, hybrid metal-dielectric or double metal MCs. In this paper we theoretically discuss the electromagnetic modes supported by the system consisting of an MQW embedded into planar resonator with semi-infinite highly doped semiconducting claddings (mirrors). We focus  on the case when intersubband frequency is comparable with the frequency of the surface plasmon of the mirrors. Then the strong resonant coupling of the intersubband excitation with the symmetric and antisymmetric surface plasmon modes leads to the formation of the intersubband-surface-plasmon polariton (ISPP) branches. The characteristics of the ISPP branches are calculated numerically using a semiclassical approach supplemented by the effective-medium approximation. The symmetric structures, where QWs uniformly fill the space between the claddings (mirrors) and asymmetric structures, where QWs occupy only half of space between the mirrors are considered. Strong dependence of the ISPP characteristics on the cavity mirror separation is demonstrated. In particular, for certain parameters of the structures we observe formation of the zero group velocity points in the ISPP branches. It was observed that the properties of the ISPP branches in the symmetric (asymmetric) structures are well interpreted by a coupled two (three) oscillator model, provided that dispersive character of mirror material is taken into account. For sake of completeness, we also briefly discuss the formation (due to the nonresonant coupling of the intersubband excitation with higher resonator modes) of the additional features - the so-called in-gap polariton branches. They are located slightly below the intersubband frequency. The demonstrated possibility of the engineering the dispersion of the ISPP branches in all-semiconductor plasmonic resonators seems to be attractive from the viewpoint of intersubband polariton optoelectronics.