III-nitride on silicon electrically injected microrings for nanophotonic circuits.

Nanophotonic circuits using group III-nitrides on silicon are still lacking one key component: efficient electrical injection. In this paper we demonstrate an electrical injection scheme using a metal microbridge contact in thin III-nitride on silicon mushroom-type microrings that is compatible with integrated nanophotonic circuits with the goal of achieving electrically injected lasing. Using a central buried n-contact to bypass the insulating buffer layers, we are able to underetch the microring, which is essential for maintaining vertical confinement in a thin disk. We demonstrate direct current room-temperature electroluminescence with 440 mW/cm2 output power density at 20 mA from such microrings with diameters of 30 to 50 µm. The first steps towards achieving an integrated photonic circuit are demonstrated.

Optical spectroscopy of two-dimensional layered (C(6)H(5)C(2)H(4)-NH(3))(2)-PbI(4) perovskite.

We report on optical spectroscopy (photoluminescence and photoluminescence excitation) on two-dimensional self-organized layers of (C(6)H(5)C(2)H(4)-NH(3))(2)-PbI(4) perovskite. Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and the phononic properties of this hybrid organic/inorganic semiconductor. In particular, exciton-phonon interaction is found to be more than one order of magnitude higher than in GaAs QWs. As a result, photoluminescence emission lines have to be interpreted in the framework of a polaron model.

Rotational and vibrational relaxation of methane excited to 2nu3 in CH4/H2 and CH4/He mixtures at 296 and 193 K from double-resonance measurements.

A series of time-resolved IR-IR double-resonance experiments have been conducted where methane molecules are excited into a selected rovibrational level of the 2nu3(F2) vibrational substate of the tetradecad and where the time evolution of the population of the various energy levels is probed by a tunable continuous wave laser. The rotational relaxation and vibrational energy transfer processes occurring in methane upon inelastic CH4-H2 and CH4-He collisions have been investigated by this technique at room temperature and at 193 K. By probing transitions in which either the lower or the upper level is the laser-excited level, rotational depopulation rates in the 2nu3(F2) substate were measured. The rate constants for CH4-H2 collisions were found to be 17.7 +/- 2.0 and 18.9 +/- 2.0 micros(-1) Torr(-1) at 296 and 193 K, respectively, and for CH(4)-He collisions they are 12.1 +/- 1.5 and 16.0 +/- 2.0 micros(-1) Torr(-1) at the same temperatures. The vibrational relaxation was investigated by probing other stretching transitions such as 2nu3(F2) - nu3, nu3 + 2nu4 - 2nu4, and nu3 + nu4 - nu4. A kinetic model, taking into account the main collisional processes connecting energy levels up to 6000 cm(-1), that has been developed to describe the various relaxation pathways allowed us to calculate the temporal evolution of populations in these levels and to simulate double-resonance signals. The different rate coefficients of the vibrational relaxation processes involved in these mixtures were determined by fitting simulated signals to the observed signals corresponding to assigned transitions. For vibration to translation energy transfer processes, hydrogen is a much more efficient collision partner than helium, nitrogen, or methane itself at 193 K as well as at room temperature.

Relaxation of Vibrational Energy in CO, HCl, CO(2), and N(2)O.

Relaxation measurements on CO and HCl excited into the first vibrational state and on CO(2) and N(2)O excited into the (00 degrees 1) vibrational state have been performed by using a fluorescence method. The rate constants associated with the de-excitation by molecular collisions have been determined at room temperature. The diffusion and accommodation coefficients have been deduced from measurements at low gas pressures, taking into account the self-absorption of the fluorescence radiation.