Optical detection of the cyclotron resonance in inhomogeneous ferromagnetic structures InGaAs/GaAs/$\delta$-$\langle$Mn$\rangle$

Structures consisting of an InGaAs/GaAs quantum well and a ferromagnetic $\langle$Mn$\rangle\,\delta$ layer separated by a narrow 3–10 nm spacer have been studied using the optically detected cyclotron resonance (ODCR). Despite strong disorder in these structures, the photoluminescence of charge carriers in the quantum well indicates ODCR upon absorption in the far infrared regions with the maximum in magnetic fields much lower than those expected for typical electron or hole cyclotron mass. The extraordinary manifestation of ODCR is due to dimensional magnetoplasma resonance of two-dimensional degenerate holes in submicron regions of the high-quality quantum well, which appear in the strong fluctuation Coulomb potential because of the mesoscopic separation of the high-density acceptor $\langle$Mn$\rangle\,\delta$ layer. Magnetic force microscopy also indicates the inhomogeneity of the structure in the plane with a characteristic scale of $\sim$ 100–200 nm below the Curie temperature of the $\langle$Mn$\rangle\,\delta$; layer. At the same time, the resonance field of ODCR in a light-emitting diode structure on the $n$-GaAs substrate is noticeably lower than that in the structure on the insulating $i$-GaAs substrate, which is explained by resonance on donors in the doped substrate.