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.