Impurity and geometry effects on the optical rectification spectra of quasi-elliptical double quantum rings

We present a theoretical study on the effects of the impurity positions and geometry change on the electronic and optical rectification spectra of GaAs/Ga0.7Al0.3As double quantum rings. The outer ring has a constant circular shape while the inner ring geometry is modified from circular to elliptic. A donor impurity is alternatively placed in two unequivalent positions, in the middle of the inner ring along x/y-axes. Specific effects in the energies and in the dipole transition moments are observed at a continuous variation of the ring dimensions. In the nonlinear optical rectification spectra, the configuration with circular rings marks the transition from two maxima spec-trum to one maximum spectrum and from red to blue???shift for y -impurity. For x-impurity, at the variation of the y-semi-axis of the internal/external ellipse limiting the inner ring, the peaks are only blue-shifted/red-shifted. The strongest red-shift appears for the most deformed inner ring.