Long-Wavelength Emission at 1.5 m from InGaAs/GaAs Quantum Dots

Long-wavelength emission at $\sim$1.5 $\mu$m at room temperature has been achieved from InGaAs/GaAs quantum dots (QDs) grown by metal-organic chemical vapor deposition. The luminescence intensity of the InGaAs QDs was enhanced by optimizing the growth interruption duration without AsH$_3$ supply just after the InGaAs QD layer had been formed. The use of In$_x$Ga$_{1-x}$As strain reducing layer to cover the InGaAs QDs shifted the QD emission wavelength to longer wavelength and made the PL wavelength reach 1.5 $\mu$m at room temperature. The luminescence from the ground state and those from excited states were seen and this coexistence, and the change in the luminescence intensity with excitation power were explained by the coexistence of unoccupied ground states and excited states in different QDs that are electrically isolated from each other in a QD ensemble.