Improved surface morphology of stacked 1.3μm InAs∕GaAs quantum dot active regions by introducing annealing processes

Abstract

The authors report a simple but effective way to improve the surface morphology of stacked 1.3μm InAs∕GaAs quantum dot (QD) active regions grown by metal-organic chemical vapor deposition (MOCVD), in which GaAs middle spacer and top separate confining heterostructure (SCH) layers are deposited at a low temperature of 560°C to suppress postgrowth annealing effect that can blueshift emission wavelength of QDs. By introducing annealing processes just after depositing the GaAs spacer layers, the authors demonstrate that the surface morphology of the top GaAs SCH layer can be dramatically improved. For a model structure of five-layer QDs, the surface roughness with the introduced annealing processes (IAPs) is reduced to about 1.3nm (5×5μm2 area), much less than 4.2nm without the IAPs. Furthermore, photoluminescence measurements show that inserting the annealing steps does not induce any changes in emission wavelength. This dramatic improvement in surface morphology results from the improved GaAs spacer surfaces due to the IAPs. The technique reported here has important implications for realizing stacked 1.3μm InAs∕GaAs QD lasers based on MOCVD.