Laser devices with stacked layers of InGaAs/GaAs quantum rings

Abstract

Stacked layers of In(Ga)As on GaAs(001) self-assembled quantum rings (QR) for laser application have been studied. Several samples with three stacked QR layers have been grown by molecular beam epitaxy with GaAs spacers from 1.5 to 14 nm. The optical and structural properties have been characterized by photoluminescence spectroscopy and by atomic force microscopy, respectively. For GaAs spacers larger that 6 nm, the stacked QR layers present similar properties to single QR layers. A semiconductor laser structure with three stacked layers of QR separated 10 nm in the active region has been grown. This spacer ensures well-developed rings with optical emission like that of a single layer. Laser diodes have been processed with 1-2 mm cavity lengths. The stimulated emission is multimodal, centred at 930 nm (77 K), with a threshold current density per QR layer of 69 A cm -2 . In this work, it is demonstrated that stacking rings is possible, and that a broad area laser with three QR layers can be fabricated successfully.