Metamorphic Quantum Dot Nanostructures For Long Wavelength Operation With Enhanced Emission Efficiency

In this work, we study the effect of additional InAlAs or GaAs barriers to enhance the confinement of carriers into quantum dots (QDs) in metamorphic QD nanostructures for long-wavelength light-emission. Such barriers are used in order to compensate for the reduction in band discontinuities that occurs when using InGaAs confining layers (CL) to red-shift the emission towards the spectral windows of optoelectronic interest; as a side effect, such a reduction causes a decrease of carrier confinement and then an inefficient emission at room temperature. By photoluminescence characterization of metamorphic QD structures grown by molecular beam epitaxy, we study the effect of barriers with different compositions, thicknesses and positions relative to QDs on the QD emission and the activation energy for confined carriers' thermal escape; our experimental data clearly show that the insertion of additional barriers results in larger emission efficiencies at room temperature and in blue-shifts of emission wavelengths. To counterbalance the blue-shift resulting from the use of these additional barriers, we introduce a red-shift by using the QD strain engineering approach, based on the reduction of QD strain, deriving from the decrease of the QD-CL mismatch; the combined use of QD strain engineering and enhanced barriers to confine carriers into QDs allows us to obtain room temperature emission up to 1.46 mu m. These findings indicate that QD strain engineering with the use of additional barriers is a viable approach to achieve efficient room temperature emission from QD structures in the long wavelength spectral windows for telecom application.