The ground and excited state luminescent transitions in self-organized InAs/InP(001) quantum islands (QIs) grown in two different matrices (In0.52Al0.48As and InP), have been studied by cw photoluminescence (PL) and time resolved photoluminescence (TRPL). PL excitation (PLE) shows that the multi-component PL spectrum measured for the InAs/InAlAs QIs is associated to ground and related excited state transitions of QIs having monolayer-height fluctuation whereas for InAs/InP QIs the multi-component PL spectrum is only due to one ground state and their related excited states. This attribution is confirmed by the recombination life times measured by TRPL which are in the 1.2-1.4 ns range for the ground state transitions and in the 90-600 ps range for the excited state transitions.
In this work we show that improved performances of small-aperture terahertz antennas can be obtained using an ion implantation process. Our photoconductive materials consist of high resistivity GaAs substrates. Terahertz pulses are generated by exciting our devices with ultrashort laser pulses. Ion implantation introduces nonradiative centers which reduce the carrier lifetime in GaAs and modify the shape of our terahertz pulses. The introduction of charge defects also induces a redistribution of the electric field between the antenna electrodes. The overall process is optimized to better control the dynamical field screening effect which has a huge influence on the amplitude of the radiated terahertz field. Results obtained as a function of the laser excitation power is discussed and comparison of the performance of these devices with conventional small-aperture antennas is given.