Ivan A. Aleksandrov

Nonradiative recombination in GaN quantum dots formed in the AlN matrix

The mechanisms of temperature quenching of steady-state photoluminescence are studied for structures with hexagonal GaN quantum dots embedded in the AlN matrix. The structures are grown by molecular beam epitaxy. The study is conducted for structures with differently sized quantum dots, for which the peak of the photoluminescence band is in the range from 2.5 to 4.0 eV. It is found that the activation energy of thermal quenching of photoluminescence varies from 27 to 110 meV, as the quantum-dot height is decreased from 5 to 2 nm. A model is suggested to interpret the results. According to the model, the photo-luminescence signal is quenched because of the transfer of charge carriers from energy levels in the quantum dots to defect levels in the matrix.

Photoluminescence kinetics slowdown in an ensemble of GaN/AlN quantum dots upon tunneling interaction with defects

The carrier recombination dynamics in an ensemble of GaN/AlN quantum dots is studied. The model proposed for describing this dynamics takes into account the transition of carriers between quantum dots and defects in a matrix. Comparison of the experimental and calculated photoluminescence decay curves shows that the interaction between quantum dots and defects slows down photoluminescence decay in the ensemble of GaN/AlN quantum dots.

Influence of defects on the photoluminescence kinetics in GaN/AlN quantum-dot structures

The influence of defects in the AlN barrier on photoluminescence decay after pulse excitation is studied for structures with GaN quantum dots in an AlN matrix. For these quantum-dot structures, it is found that the initial part of the decay curves corresponds to fast photoluminescence decay. Comparison of the photoluminescence-decay curves for the GaN/AlN quantum-dot structures and AlN layers without quantum dots shows that fast decay is defined by the contribution of the photoluminescence band related to defects in the AlN matrix.

Photoluminescence of AlGaN/GaN heterostructures with two-dimensional electron gas and unknown acceptor center

The radiative recombination of two-dimensional electron gas (2DEG) and holes from bulk GaN in Al-GaN/GaN heterostructures are characterized with use of photoluminescence (PL) spectroscopy. The samples were grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) technique. PL was excited by a continuous He-Cd laser and a pulse N2 laser at 5 K. Series of PL bands located below the donor bound excitons band have been observed. Two of these PL bands have been observed both at continuous and pulse excitation. These PL bands were found earlier and connected with the recombination of 2DEG electrons at the first and the second levels in the quantum well with free holes. At the same time three new PL bands located below these PL bands appear only at pulse excitation. We attribute these PL bands to the recombination of 2DEG electrons with holes located on excited levels of deep acceptors. We have also observed PL bands attributed to the recombination in donor-acceptor pairs with an unknown acceptor. The presence of this acceptor center might be the reason for appearance of new three bands attributed to the recombination of 2DEG electrons.