The photoluminescence and excitation of luminescence spectra of a series of samples containing
two CdTe layers D1 and D2 with a nominal thickness of 1.5 and 4 monolayers in a ZnTe matrix were studied.
The samples differ in the width of the ZnTe spacer separating the D1 and D2 inserts and constituting 15, 25,
35, 45 and 55 monolayers (samples no. 1–5, respectively). ZnTe layers are grown on a GaAs substrate by the
standard molecular beam epitaxy mode, while CdTe inserts are grown in atomic layer epitaxy mode. It is
shown that when the barrier thickness is less than 25 monolayers electronic states in the quantum wells
formed by D1 and D2 layers are tunnel-coupled, and only one band is recorded in the emission spectrum,
caused by the recombination of excitons in the deep quantum well. At larger thicknesses of the spacer, two
bands I1 and I2 are observed in the luminescence spectrum, which are associated with the recombination of
excitons in shallow (D1) and deep (D2) wells, respectively. It was found that the intensity ratio I1/I2 significantly
depends on the energy and intensity of the excitation. Possible origin of these dependences are discussed.