We have studied photoinduced self-oscillation characteristics in GaAs/AlGaAs multiple shallow quantum-well diodes as a function of bias voltage and laser power. Under the illumination of a laser of wavelength corresponding to the exciton absorption energy, the I-V curve of the diode revealed a large negative differential conductance region where the electrical and optical oscillations were observed in the same phase. The oscillation frequency was widely tuned by either bias voltage or laser power, and this demonstrates a large potential of the device scheme for the electrical and optical signal generators with wide frequency tunability. (C) 1999 American Institute of Physics. [S0003-6951(99)01317-0].