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Research Unipolar light emitting device Thus far attention has focussed on the interband optical properties, and intersubband transitions have been largely ignored. However, the problem of obtaining good p-type conductivity in these materials currently blocks further development of high power lasers and light-emitting diodes. To overcome these difficulties and to explore other possible optoelectronic applications of nitrides we propose an alternative approach based on intersubband transitions which has already been successfully used in cascade light-emitting devices for the mid infra-red. Quantum cascade and disk lasers will be fabricated using this intersubband laser structures. A unipolar light emitting device (ULED) based on III-nitride superlattices for generation of visible light is suggested. The main idea is to create the analogue of an n-p junction between two n-type superlattices with ? shallow and ? deep subband. The superlattice with the shallow subband acts ?s an effective n-type semiconductor, whereas the other superlattice 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 sub-band superlattice. The quantum efficiency of these transitions could be enhanced by inserting between the 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 directly electrically pumped through the superlattice subbands. The efficiency of the device is limited by the non-radiative energy relaxation channel related to the phonon emission and is rather low for the simple ULED without an active layer or a ULED with a single quantum well active layer. ? significant increase in the efficiency can be achieved with use of an 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.
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