High speed characterization of p-i-n- photodetectors by nonlinear photocurrent spectroscopy

By analyzing the photocurrent nonlinearity, observed under excitation with two successive picosecond optical pulses, we investigate the carrier transport and electric field recovery in high-speed p-i-n photodetectors containing In0.2Ga0.8 As/GaAs quantum wells in the intrinsic region. The nonlinearity originates from the distortion of the electric field by the free carriers generated by the leading pulse, which changes the absorption of the subsequent pulse. The nonlinear signal is resonantly enhanced by orders of magnitude at suitable excitation wavelengths due to excitonic resonances. For the recovery time of the electric field we find values less than 15 ps.