Tunnel injection structures based on InGaAs/GaAs quantum dots: optical properties and energy structure

The limited speed of direct modulation due to the significant population of hot carriers in quantum dots (QD) is a major drawback of the application of QD based lasers in fibre optics telecommunication. One of the most promising methods of alleviating this problem is the design of tunnel injection (TI) structures, where already cold carries are injected by means of tunnelling through a thin barrier from an adjacent quantum well (QW) directly to the QD ground state. We have investigated the properties of TI structures consisting of an In_xGa_1−xAs quantum well and a layer of self-assembled In_0.6Ga_0.4As/GaAs quantum dots versus the properties a reference QD sample. Photoreflectance spectroscopy is applied to determine the energies of optical transitions in this complex system. The obtained energies are then used to verify the reliability of the calculations in the 8 band kp model, which take into account the realistic geometry of the dots, influence of the strain and the coupling between the dot layer and the injector quantum well. Finally, time resolved photoluminescence (PL) experiment is performed at low temperature and its results are related to the acquired structure of confined levels. The influence of the tunnelling process on PL rise and decay times is explained.