Novel mechanisms of optical harmonics generation in semiconductors

Spectroscopic study of diamagnetic, diluted magnetic, and magnetically ordered semiconductors reveals several novel mechanisms of optical harmonics generation. It is found that Landau-level orbital quantization of the band energy is a key mechanism for magnetic-field-induced second harmonic generation (MSHG) in diamagnetic semiconductors GaAs and CdTe. The giant Zeeman spin-splitting of electronic states is essential for MSHG in diluted magnetic semiconductors (Cd,Mn)Te. Both mechanisms involving the optical nonlinearities of electric-dipole type take place in noncentrosymmetric semiconductors. Spin-induced second harmonic generation (SHG) is observed at the band gap in magnetic centrosymmetric semiconductors EuTe and EuSe. This mechanism involving the optical nonlinearities of magnetic-dipole type is essential for centrosymmetric semiconductors. The magnetic field and temperature dependencies demonstrate that the nonlinear processes arise due to novel types of optical nonlinearities caused by the external magnetic field. The observed mechanisms of optical nonlinearities open access to a wide class of centrosymmetric and noncentrosymmetric systems by harmonics generation spectroscopy. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim