Enhancement of the photocurrent density generated by internal moving space charge electric fields in semi-insulating GaAs multiple quantum wells is observed when the sample is biased with a high speed, zero-mean square wave electric field which increases the internal space charge electric field strength. Tunability of the space charge field formation time is also demonstrated by adjusting the amplitude of the bias signal. This technique can be used to enhance the sensitivity of optical doppler frequency measurements based on moving space charge field effects in photoconductive semiconductors. Electronic tunability of the space charge field formation time also adds versatility in optical power spectrum analysis applications. © 1998 American Institute of Physics.