Room temperature luminescence from self-organized InxCa1-xAs/GaAs (0.35<x<0.45) quantum dots with high size uniformity

Self-organized,growth of InxGa1-xAs/GaAs quantum dots (QD) For 0.5 < x are studied by time-integrated. time-resolved and temperature-dependent photoluminescence (PL). Low-temperature photoluminescence demonstrates that the critical composition is' needed for the formation of 3D islands is between 0.3 and 0.35. This is also supported by reflection high-energy electron diffraction (RHEED) measurements and agrees well with our theoretical predictions that a misfit of > 2% is needed, from thermodynamic considerations, for the onset of 3D growth. The presence of fine excitonic features superimposed on the emission peaks confirms that the second peak observed in the PL spectra of quantum dots is from an excited slate transition. We believe that the saturation of the ground-state emission observed under moderately high excitation photon densities is due to the long decay time constant (similar to 2.2 ns) as measured by time-resolved photoluminescence. Temperature variation of luminescence intensity shows a sharper decay for the ground-state emission than fur the excited-state emission, Room-temperature luminescence is thus dominated by the excited state emission. Broad area lasers made from separate confinement heterostructure (SCH) laser structures with In0.4Ca0.6As quantum dots as the active region showed lasing from excited state, with J(th) = 650 A/cm(2), and the single-mode ridge lasers gave a modulation bandwidth of 5 GHz at 2.5I(th).