Defect dissolution in strain-compensated stacked InAs/GaAs quantum dots grown by metalorganic chemical vapor deposition

We report a highly effective growth technique to both dissolve large islands and prevent further defect propagation in closely spaced (15 nm) stacked quantum dot (QD) active regions while maintaining an emission wavelength > 1.3 mu m. Island dissolution is accomplished via an In flush, which is an AsH3 pause inserted into the growth sequence just after each QD layer is capped. The low V/III ratio enables the flushing of surface In atoms from the defect sites while the fully capped QDs remain intact. This technique eliminates the need for in situ annealing that activates the In flush in other growth scenarios and results in large emission blueshift. Strain propagation within the closely spaced QD stacks is reduced by GaP strain-compensation layers. Room-temperature photoluminescence confirms ground-state emission wavelength > 1.34 mu m. Atomic force microscopy and transmission electron microscopy confirm improved surface morphology and crystalline quality of stacked QD active regions. The resulting structures are suitable for long-wavelength lasers, especially vertical cavity surface-emitting laser applications in which high modal gain is attractive. (c) 2005 American Institute of Physics.