Marcio José Mörschbächer

Strain relaxation of pseudomorphic Si1-xGex/Si(100) heterostructures after Si+ ion implantation

The strain relaxation of pseudomorphic Si1−xGex layers (x=0.21,…,0.33) was investigated after low-dose Si+ ion implantation and annealing. The layers were grown by molecular-beam epitaxy or chemical vapor deposition on Si(100) or silicon-on-insulator. Strain relaxation of up to 75% of the initial strain was observed at temperatures as low as 850°C after implantation of Si ions with doses below 2×1014cm−2. We suggest that the Si implantation generates primarily dislocation loops in the SiGe layer and in the underlying Si which convert to strain relaxing misfit segments. The obtained results are comparable to strain relaxation achieved after He+ implantation with doses of 1–2×1016cm−2.

Structural and optical properties of InP quantum dots grown on GaAs(001)

We investigated structural and optical properties of type-II InP/GaAs quantum dots using reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction, and photoluminescence techniques. The InP dots present an efficient optical emission even when they are uncapped, which is attributed to the low surface recombination velocity in InP. We compare the difference in the optical properties between surface free dots, which are not covered by any material, with dots covered by a GaAs capping layer. We observed a bimodal dispersion of the dot size distribution, giving rise to two distinct emission bands. The results also revealed that the strain accumulated in the InP islands is slightly relieved for samples with large InP amounts. An unexpected result is the relatively large blue shift of the emission band from uncapped samples as compared to capped dots.

Carrier dynamics in stacked InP∕GaAs quantum dots

We investigated two stacked layers of InP∕GaAs type-II quantum dots by transmission electron microscopy and optical spectroscopy. The results reveal that InP quantum dots formed in two quantum dot layers are more uniform than those from a single layer structure. The thermal activation energies as well as the photoluminescence decays are rather independent of the separation between quantum dot layers and the presence of the second layer. The quantum dot optical emission persists for thermal activation energy larger than the calculated exciton binding energy. The photoluminescence decay is relatively fast for type-II alignment.

Carbon deposition in Si as a consequence of H and He irradiations: A systematic study

In the present work we have investigated the influence of different parameters that determine the C deposition on a Si target. Among them we have studied the pressure of the irradiation chamber, the implantation fluence, the current density, the target temperature, the energy of the beam, the charge state of the ion, the ion species and the molecular state of the irradiation beam. In order to determine the quantity of C deposited on the Si substrate we have used the Rutherford backscattering/channeling technique together with the resonant 12C(α,α)12C reaction. After careful analysis we arrived at the conclusion that the real independent parameters are the pressure of the irradiation chamber, the temperature of the target, the irradiation time and the electronic stopping power of the ion–target combination.