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.
We demonstrate vertical integration of InGaAs mesa photodiodes with InGaAsP rib waveguides employing an intermediate optical impedance matching layer. The diode length necessary for 90% light absorption at 1.52 μm wavelength was 42 μm, a threefold reduction in diode length with respect to previous work employing similar waveguides without a matching layer. The quantum efficiency was observed to be almost independent of the optical wavelength and polarization. The influence of spatial transient intensity redistribution effects on these devices is investigated in detail.
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