Carrier induced transient electric fields in a p-i-n InP-InGaAs multiple-quantum-well modulator

Low-power time-resolved pump-probe measurements made on a InP-In/sub 0.53/Ga/sub 0.47/As p-i-n multiple-quantum-well optical modulator are presented. The results show a nonzero signal at negative delays whose magnitude and sign exhibit a strong dependence upon the wavelength and bias. The overall behavior after zero delay, in particular the signal rise and fall times, also depends strongly upon these parameters. A theory, based upon electric field variations due to carrier motion in the intrinsic region of the device, is developed to explain the results. It is found that the signal at negative delay is due to hole space charge trapped in the quantum wells, while the fast effects after zero delay are due to the rapid emission of electrons which cause a temporary reduction in potential across the device. This is followed by diffusive conduction within the contact layers which restores the potential to its former value. The rich variety of signal responses is attributed to transient Stark shifts which vary greatly with well position due to the nonuniformity of the dynamic change in the electric field. Calculated signal responses are in excellent agreement with the experimental results.