Free-carrier effects in GaAs single modulation-doped quantum well as applied to active Q-switching of injection lasers

(Received 23 January 1992, revised 23 October 1992, accepted 16 February 1993)

Abstract
Free carrier effects in a modulation-doped GaAs QW placed in the n-region of a p-n junction were successfully used to obtain active Q-switching in a two-section GaAs/A1GaAs DH laser structure. The modulator section 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  cm ^-2 by external bias voltage. Only about 100 mV of the modulating voltage was necessary to provide stable active Q-switching. The threshold injection current density ranged from 400 to 800 A/cm ². 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.