Highly enhanced second-order nonlinear susceptibilities in tailored GaN–AlGaN–AlN quantum well structures

A tailoring proposal for design of the strained quantum well structures, optimized with respect to the intersubband resonant second-order nonlinear properties, is presented in this article. A genetic-algorithm-based method is used in order to obtain the optimal potential shape, doping concentration and location in strained GaN–AlGaN–AlN quantum wells, and the structures are analyzed by a numerical solution of the Schrödinger–Poisson self-consistent method. In general form two types of asymmetric structures with remarkable results are obtained with different resonant frequencies, and in both cases results show a considerably high enhancement in the magnitude of the second-order nonlinear susceptibilities in higher resonant frequencies in comparison with a single quantum well structure with the same well width (5.02×10−8 m/V at ℏω=0.41eVto 2.9×10−5 m/V at ℏω=0.44eVand 2.43×10−5 m/V at ℏω=0.604eV). The optimized structures exhibit considerable absorption coefficient and electroabsorption properties due to high dipole transition matrix element, high dopant concentration and reasonable Fermi level.