M. Zamfirescu

Photoluminescence of individual doped GaAs∕AlGaAs nanofabricated quantum dots

Dilute arrays of GaAs∕AlGaAs modulation-doped quantum dots with same sizes fabricated by electron beam lithography and low impact reactive ion etching exhibit highly uniform luminescence lines. Single quantum dots display spectral emission with peak energies and linewidths linked largely to the geometrical diameter of the dot and to the built-in electron population. Multicharged excitonic and biexcitonic emission intensities have activation energy of about 2meV. These results highlight the potential of high quality nanofabricated quantum dots for applications in areas that require fine control of optical emission.

Role of the host matrix in the carrier recombination of InGaAsN alloys

We present an experimental study of the carrier recombination dynamics in high-quality (InGa)(AsN)/GaAs and Ga(AsN)/GaAs quantum-well structures after picosecond excitation. A comparison among samples with and without nitrogen and with different In concentration shows that nonradiative channels originated in the host matrix [i.e., (InGa)As and GaAs] play a dominant role in the recombination dynamics of these heterostructures.

Characterization of hydrogen passivated defects in strain-engineered semiconductor quantum dot structures

The effects of hydrogen incorporation on carrier relaxation and recombination efficiencies in a large series of InAs self-assembled quantum dot structures deposited on InGaAs lower confining layers with different thicknesses and compositions have been addressed. With increasing H dose we observe an improvement in the radiative efficiency. By comparing steady state and time resolved photoluminescence measurements, it is established that the H passivation does not enhance the relaxation and capture efficiencies, but instead directly improves the emission yield from carriers in the dots. We therefore conclude that the H-passivated defects are located nearby, or even inside, the dots.

Dynamical nonlinearity in strained InGaAs (311)A sidewall quantum wires

Significant optical nonlinearity has been found in InGaAs (311)A sidewall quantum wires by means of time resolved photoluminescence measurements. A strong reverse quantum confined Stark effect has been observed and attributed to the dynamical screening of both the internal piezoelectric field and the Coulomb interaction between carriers. The time evolution of the quantum wire emission has been reproduced by means of self-consistent calculations that take into account excitonic effects, strain, and induced piezoelectric charges.

Carrier localization in (InGa)(AsN) alloys

We investigate the origin of radiative recombination in (InGa)(AsN)/GaAs single quantum wells by means of continuous wave and time-resolved photoluminescence (PL) measurements. Samples with different indium and nitrogen concentration were investigated. An analysis of the whole set of data for different excitation densities and lattice temperatures, T, is reported. This analysis provides insights into radiative and non-radiative processes ruling the recombination dynamics and shows the predominant contribution of localized state emission at low T. The nature of these states is further studied by measuring the time necessary (rise time) for their population. We find that the PL rise time in (InGa)(AsN) is independent of temperature and detection energy, thus being not conclusive about the origin of the states involved in the emission processes. On the contrary, magneto-PL measurements show that the shift of the PL peak energy induced by a magnetic field, B, decreases sizably and changes its dependence on B from linear to quadratic when going from low to high temperature. This counterintuitive result shows that radiative recombination at low temperature (T<100 K) is not excitonic, contrary to previous assignments, and is due to loosely bound electron-hole pairs in which one carrier is localized by N-induced potential fluctuations and the other carrier is delocalized.