We have observed the abnormal photocurrent-voltage (I-V) behavior in GaAs/AlGaAs multiple shallow quantum wells p-i-n diodes. Under the illumination of a laser, two current plateaus were developed at the negative conductance region of the I-V curve, along with some hystereses depending on the scan direction. At the first plateau, two major oscillations of similar to 120 kHz and similar to 37 MHz were observed with several minor oscillations of frequencies below the latter, while this latter component was uniquely at the other plateau. Analyzing the electrical and the optical oscillations, we explain that one hysteresis at the first plateau was due to the low frequency bias-circuit oscillations, whereas the other at the next plateau was attributed to the intrinsic behavior of the p-i-n diode. (C) 1998 American Institute of Physics.