Single- and double-resonant enhancement of second-harmonic generation in asymmetric AlGaN/GaN/AlGaN quantum well heterostructures

The second-harmonic generation susceptibility is theoretically investigated based on the compact density-matrix formalism in two- and three-level AlGaN/GaN systems. The electronic states and their related wave functions were calculated by solving self-consistently the Schrodinger-Poisson equations within the effective mass and Hartree approximations. The presence of spontaneous and piezoelectric polarizations is taken into account in the modeling part. It was revealed from the relevant results that (i) the second-order susceptibility shows a multiple peak structure due to intersubband and their corresponding virtual transitions, (ii) the use of a back doping as well as the optimization of the layer widths in delta-doped AlGaN/GaN asymmetric quantum wells improved considerably the second-harmonic susceptibility, and (iii) the three-level AlGaN/GaN system is the most efficient structure, which generates the second-harmonic with a significant intensity up to 4.36x10(-5)mV(-1). Numerical results of the present work could lay the basis for research in AlGaN-related optoelectronic device applications.