Observation of plasma and magnetoplasma resonances of two-dimensional electrons in a single $\mathrm{MgZnO}/\mathrm{ZnO}$ heterojunction

The magnetoluminescence of the two-dimensional electron system in a single $\mathrm{Mg}_x\mathrm{Zn}_{1 -x} \mathrm{O}/\mathrm{ZnO}$ hetero-junction ($x = 0.02$) at a temperature of $0.3$ K in magnetic fields up to $14$ T has been studied. The concentration of two-dimensional electrons in the structure under study has been determined from the oscillations of the luminescence intensity as a function of the magnetic field. The value thus obtained is close to the one derived from transport measurements. The resonance corresponding to plasma excitations of two-dimensional electrons has been observed using optical detection of microwave absorption. In a magnetic field, the lower branch of magnetoplasma excitations, which corresponds to the propagation of edge magnetoplasmons in a structure with nearly square geometry, has been observed and investigated.