Self-assembling quantum dots for optoelectronic devices on Si and GaAs

The formation of self-assembling quantum dots for the different strained material systems Ge/Si, InAs/GaAs and InP/GaInP in molecular beam epitaxy is discussed. Intense 1.55 and 1.3 mum room temperature photoluminescence is achieved for stacked Ge dots in Si and single InAs dot layers in GaAs, respectively. Small InP/Ga0.52In0.48P quantum dots emit in the visible red spectrum. Strain-induced vertical alignment, size modification and interdiffusion for stacked dot layers are studied. A blue shift of the ground state transition energy is observed for relatively large size stacked Ge and InAs dots. This is ascribed to enhanced strain driven intermixing in vertically aligned islands. For extremely small and densely stacked InP and InAs dots the stronger confinement causes a red shift of the ground state emission. InP/Ga0.52In0.48P quantum dot injection lasers with coupled three-fold stacked InP dots are presented. Ground state lasing is observed at room temperature with a maximum output power up to 250 mW. The threshold current density at 300 K is j(thr) = 2.3 kA/cm(2), and an external quantum efficiency of eta (ext) = 8.5% is measured for a 2 mm long laser cavity. (C) 2001 Elsevier Science B.V. All rights reserved.