Molecular beam epitaxy (MBE) growth of composite (In,Al)As/(In,Ga)As vertically coupled quantum dots and their application in injection lasers

Injection lasers based on self-organized (In,Ga)As/(Al,Ga)As quantum dots (QD) suffer from the gain saturation due to the limited amount of QD states participating in lasing. In the present work, we demonstrate the direct increase in the areal density of (In,Ga)As QDs. We used an array of (In,Al)As QDs demonstrating considerably higher density than Al-free QDs as nucleation centers for the (In,Ga)As QD formation. Finally, composite vertically coupled (In,Al)As/(In,Ga)As QDs with increased areal density are formed, which is confirmed by photoluminescence and TEM. Using the denser array of (In,Al)As/(In,Ga)As QDs in the active region of injection laser leads to the increase in modal gain, reduction in threshold current density at high mirror loss, and increase in maximum output power. (C) 1999 Elsevier Science B.V. All rights reserved.