III-Nitride Unipolar Light Emitting Devices

Abstract

Unipolar light emitting device based on III-nitride superlattices for the generation of visible light is suggested. The main idea of the unipolar light emitting device (U-LED) is to create the analogue of an n–p junction between two n-type superlattices with a shallow and a deep subband. The superlattice with the shallow subband acts as an effective n-type semiconductor, whereas the superlattice with deep subband plays the role of an effective p-type semiconductor. The radiation arises due to the electron transitions from the shallow subband superlattice into the deep subband superlattice. The conduction band off-set between AlN and InN is about 3 eV and this value can be reduced using the alloys of AlGaN. This allows one to get electron transitions between two superlattices based on these alloys with energies in the range of 0 to 3 eV, which covers the visible and the infrared range of the spectra. The quantum efficiency of these transitions could be enhanced by inserting between two superlattices some optically active layer with two quantum states, which can be a specially designed quantum well, impurity layer or quantum dot layer. The active layer can be pumped directly electrically through the superlattice subbands. The efficiency of the device is limited by the non-radiative energy relaxation channel related to phonon emission and is rather low for the simple U-LED without an active layer or an U-LED with a single quantum well active layer. A significant increase in the efficiency can be achieved with the use of the active layer doped with deep acceptors. In this case the optical transitions take place from the quantum well subband of the active layer into the deep acceptor impurity band. The transition metals Fe and Ni are considered as possible deep acceptors for the active layer in GaInN/AlN superlattices.