Second-harmonic generation in asymmetric Si/SiGe quantum wells

The observation of infrared second-harmonic generation in asymmetric Si/SiGe p-doped quantum wells is reported. The generated signal stems entirely from valence intersubband transitions, since bulk Si, with an inversion symmetric crystal structure, has a zero second-order susceptibility. The experiments were performed using a Q-switched CO2 laser operating at 10.56 μm and give a nonlinear susceptibility of 5×10−8 m/V.