Abstract-Multisubband Plasmons in Doped Zn O Quantum Wells

Jose M. Ulloa, Nolwenn Le Biavan, Romain Peretti, Francois H. Julien, Jerome Faist, Jean-Michel Chauveau, Adrian Hierro,

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.10.024005

Intersubband (ISB) transitions are of high significance for light-emitting and light-detecting devices in the infrared and, when involving large electron densities, for plasmonics and strong light-matter coupling physics. Here it is observed that the simultaneously occurring fundamental and excited-state ISB transitions in highly-doped, m-plane $\mathrm{Zn}O/{\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}O$ multiple quantum wells, couple into a single collective oscillation: the multisubband plasmon (MSP). With 2D electron densities up to $4\times {10}^{13}{\mathrm{cm}}^{-2}$, an outstanding regime is reached in which the observed MSP frequency is three times larger than that of the fundamental ISB transition as a result of depolarization. This effect is analyzed using a dielectric tensor for $\mathrm{Zn}O$ including the interaction of the light with the lattice, the in-plane free electrons, and the off-plane MSP. The impact of the broadening of the MSP and its interaction with phonons is discussed. The results presented here show the potential of $\mathrm{Zn}O/{\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}O$ for infrared optoelectronic applications, which can be extended to the THz range with appropriate design of the quantum wells.

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