Influences of the spacer layer growth temperature on multilayer InAs/GaAs quantum dot structures

The growth temperature of spacer layers (SPLs) is investigated as a means to obtain identical layers for multilayer quantum dot (QD) structures. A 5-layer 1.3-mum InAs/GaAs QD structure with 50-nm GaAs SPLs served as a model system. It is found that the growth temperature of the GaAs SPLs has pronounced effects on both the structural and optical properties of the InAs QDs. For GaAs SPLs grown at a low temperature of 510degreesC, dislocations are observed in the second and subsequent layers, a result of significant surface roughness in the underlying spacer layer. However by increasing the growth temperature to 580degreesC for the final 35 nm of the 50-nm GaAs SPLs, a much smoother surface is achieved, allowing the fabrication of essentially identical, defect free QD layers. The suppression of defect formation enhances both the room-temperature photoluminescence efficiency and the performance of 1.3-mum multilayer InAs/GaAs QD lasers. An extremely low continue-wave room-temperature threshold current density of 39 A/cm(2) is achieved for an as-cleaved 5-layer device with emission at 1.306 mum and ground state operation up to 100degreesC. (C) 2004 American Institute of Physics.