Second-harmonic generation investigations of ${\mathrm{Zn}}_{1-x}{\mathrm{Cd}}_x\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ asymmetric coupled quantum wells

Second-order nonlinear optical properties of strained ${\mathrm{Zn}}_{1-x}{\mathrm{Cd}}_x\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ asymmetric coupled quantum wells (ACQW’s) have been investigated by using the reflective second-harmonic generation (SHG) technique. Compared with the SHG intensities in ZnSe bulk material, a significant enhancement of the signals was observed in ACQW’s due to the centrosymmetry-breaking effect resulting from the strong-coupling interaction between adjacent quantum wells. The second-harmonic intensity was also found to increase with decreasing cadmium concentration x because of the second-harmonic off-resonance effect. Moreover, the SHG intensity versus the sample azimuthal angle shows an obvious in-plane anisotropy with a period of 180°, and our numerical calculations of the SHG dependence on azimuthal or polarization angle agreed well with experimental results.