Coupled quantum systems are very desirable structures due to potential applications in spintronics and quantum computing. Particularly interesting are coupled objects with different dimensionality like quantum wells (QWs) –2D structures and quantum dots (QDs) –0D structures. By combining such different objects one can think about an unusual combination of physical properties. For example, spin relaxation in QWs is very fast but it is rather low in QDs. Therefore structure with coupled QWs and QDs could be used for efficient spin orientation of carriers in QWs and further injection of such polarized carriers to QD where spin will be preserved for a long time. Polarization of carriers in QDs can be subsequently transferred to magnetic ions and in particular to a single magnetic ion in a QD.

However, for efficient tunneling QW energy should be equal to or slightly larger than QDs energy but due to quantum confinement larger objects like QWs exhibit typically higher energy than smaller objects like QDs. Moreover, QWs should be not strained too much while QDs are typically formed in strained structure. Therefore it is difficult to find a good material combination for the realization of coupled QWs and QDs.

We propose coupled QWs and QW dots based on the (Cd, Mg)Te system, where QW is made of (Cd, Mn, Mg)Te with low Mg content, the barrier is made of (Cd, Mg)Te with high Mg content, and QDs are made of CdTe:Mn. Our system is realized using molecular beam epitaxy and investigation is based on optical spectroscopy at low temperatures. Optical spectra confirm that the energy of obtained QWs is slightly higher than the energy of QDs. Moreover, in a series of samples with various positions of QD versus QWs we observe either rapid transfer of energy from QWs to QDs, or efficient luminescence of QWs.

Authors: K. Połczyńska, E. Janik, P. Kossacki and W. Pacuski


Vol. 132 (2017)

DOI: 10.12693/APhysPolA.132.369