Sub-wavelength probing and modification of photonic crystal nano-cavities

In this work we present a sizeable and reversible spectral tuning of the resonances of a two-dimensional photonic crystal nano-cavity by exploiting the introduction of a sub-wavelength size glass tip. The comparison between experimental near-field data and results of numerical calculations shows that the spectral shift induced by the tip is proportional to the local electric field intensity of the cavity mode. This observation proves that the electromagnetic local density of states in a microcavity can be directly measured by mapping the tip-induced spectral shift with a scanning near-field optical microscope. Moreover, a non-linear control on the cavity resonance is obtained by exploiting the local heating induced by near-field laser excitation at different excitation powers. The temperature gradient due to the optical absorption results in an index of refraction gradient which modifies the dielectric surroundings of the cavity and shifts the optical modes.     

Time-resolved luminescence of ZnIn2S4 at low temperature

Summary A detailed study of the time-resolved luminescence of ZnIn₂S₄ after pulsed-laser excitation at 30 K is presented. Results are given on the dependence of the emitted PL intensity at different emission wavelengths on the excitation intensity, on the time-resolved spectra in the range (0÷10⁻¹) s of delay time with respect to excitation and on the time decay of the luminescence intensity for different emission wavelengths. The results are discussed in the framework of a simple model for the recombination processes at low temperatures yielding a good overall agreement with the experimental data. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Carrier recombination dynamics in self-ordered InAs quantum dots

Il Nuovo Cimento D - A photoluminescence study of self-ordered InAs quantum dots grown by molecular beam epitaxy on a GaAs substrate is reported. Short pulses and high excitations have been used in...     

Polarization field effects on the recombination dynamics in low-In-content InGaN multi-quantum wells

The interplay of polarization fields and free carrier screening in In_xGa_1−xN/GaN (0.03<x<0.07) multiple quantum wells is studied by combining photoluminescence (time-integrated and time-resolved) and cathodoluminescence studies, in an excitation density range from 10⁸ to 10¹² cm⁻² of generated e–h pairs. For such low In content, the quantum-confined Stark effect is verified to rule the recombination dynamics, while effects of carrier localization in potential fluctuations have a minor role. Efficient field screening is demonstrated in CL steady-state high-injection conditions and in PL time-resolved experiments at the maximum excitation density. Under recovered nearly flat band conditions, quantum confinement effects are revealed and a high and possibly composition-dependent bowing parameter is extrapolated. Information on radiative and non-radiative rates for carrier recombination in the wells is obtained, both from steady-state and from time-resolved experiments, modelling the carrier dynamics in the framework of a theoretical rate equation model, which calculates electronic states and recombination rates in the nanostructure by coupling complete self-consistent solutions of Schrödinger and Poisson equations.     

Picosecond spectroscopy of hydrogenated MBE-GaAs

Picosecond-resolved and steady-state photoluminescence at LHe temperature in low-energy ion-gun hydrogenated GaAs/GaAlAs heterostructures are reported. The exciton in the GaAs layer shows an increase in lifetime — up to a factor of 3 — for moderate hydrogenation, followed by a sharp decrease below the value for the untreated sample, for higher H doses. Luminescence efficiency shows a consistent behavior. Incorporation of H generates a strong D-A band falling 64 meV below the gap energy. The behavior for heavy hydrogenation indicates the formation of a new type of deep defect, not ascribed to surface damage, because of the protective GaAlAs layer, plus the fact that the excitonic emission of the latter shows no variation.