FREE-CARRIER EFFECTS IN GAAS SINGLE MODULATION-DOPED QUANTUM-WELL AS APPLIED TO ACTIVE Q-SWITCHING OF INJECTION-LASERS

Free carrier effects in a modulation-doped GaAs QW placed in the n-reg ion of a p-n junction were successfully used to obtain active Q-switch ing in a two-section GaAs/AlGaAs DH laser structure. The modulator sec tion uses the blue shift of the QW absorption edge due to band filling by a 2D electron gas whose concentration could be controlled between 0 and 8 x 10(11) cm-2 by external bias voltage. Only about 100 mV of t he modulating voltage was necessary to provide stable active Q-switchi ng. The threshold injection current density ranged from 400 to 800 A/c m2. The modulation bandwidth is estimated to be not less than 4-5 GHz. A simple electrostatic model is suggested to describe electrooptical phenomena in a modulation-doped QW which underlie the operation of the device.