The study of hybrid systems MPA@SWNT of peapods kind involving photoactive molecules (MPA) confined in single-walled carbon nanotubes (SWNT) find its motivation in the possibility of modulating the physical properties of the nanotubes. Many experimental studies using vibrational spectroscopy in particular are interested in the physical properties of these hybrid systems. The key point of this issue is the nature of the interaction between the nanoconfinement matrix and MPAs, and the complexity of its study requires a comparison between experimental data and modelizations. In this work, we study the hybrid systems MPA@SWNT through modeling performed in different settings ranging from the use of molecular dynamics (MD) to that of the density functional theory (DFT). The limiting factor in DFT calculations is the computation time. the latter which varies in N3 (N is the number of atoms) increases drastically when N exceeds a hundred atoms for energy minimizations calculation, and even more for phonons calculations. In this context, the study of hybrid systems with organic MPAs is delicate. Indeed, the MPAs are complex molecules generally comprising side chains for the solubility of the system. For example, the smallest hybrid system studied, which consists on encapsulating a single molecule of thiophene oligomer functionalized with methyl groups at the edges inside an (11,0) nanotube contains 344 atoms. For the computation time not to be prohibitive, we tested different methods of simulation of the vibrational spectra of MPA@SWCNT: molecular dynamics, tight binding, and hybrid calculations MD/DFT. We discuss in details the results comparing models with experimental data for 1D thiophene oligomer molecules encapsulated inside nanotubes.

This book gives a survey of the current state of the art of a special class of nitrides semiconductors, Wurtzite Nitride and Oxide Semiconductors. It includes properties, growth and applications. Research in the area of nitrides semiconductors is still booming although some basic materials sciences issues were solved already about 20 years ago. With the advent of modern technologies and the successful growth of nitride substrates, these materials currently experience a second birth. Advanced new applications like light-emitters, including UV operating LEDs, normally on and normally off high frequency operating transistors are expected. With progress in clean room technology, advanced photonic and quantum optic applications are envisioned in a close future. This area of research is fascinating for researchers and students in materials science, electrical engineering, chemistry, electronics, physics and biophysics. This book aims to be the ad-hoc instrument to this active field of research.

Light-emitting devices based on high-Al content (Al,Ga)N suffer from high densities of dislocations or other point defects, counterbalanced by the carrier localization arising from disorder in the ternary alloy. One way to improve the internal quantum efficiency is the controlled Si-doping of AlxGa1-xN/AlyGa1-yN multi-quantum wells, which was assigned to the reduction of point defects by reduction of internal strains, for some ideal concentration of Si. Time-resolved photoluminescence (TR-PL) can be used [S. F. Chichibu et al., Appl. Phys. Lett. 99, 051902 (2011)] to try and correlate the observed PL time-decays with the density of defects, in relation with the nonradiative recombination probability of photoexcited carriers. We present TR-PL studies of MOVPE-grown Si-doped AlxGa1-xN/AlyGa1-yN multi-quantum wells with typical values of x=0.6 and y=0.7 and of AlxGa1-xN epilayers with x up to 0.86. High-Al content MQWs and epilayers exhibit similar bi-exponential PL decay dynamics, with the slower component rapidly quenched when T is increased. The fast decay component remains in the nanosecond range at all temperatures and the PL intensity loss is limited by carrier localization.

Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p-GaN or 1300 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photogeneration near the surface region by above bandgap excitation. Taking into consideration the absorption in the active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be about 92 +/- 7 nm and 68 +/- 7 nm for Mg-doped p-type GaN and 432 +/- 30 nm and 316 +/- 30 nm for unintentionally doped n-type GaN, respectively. Cross-sectional cathodoluminescence line-scan measurement was performed on a separate sample and the diffusion length in n-type GaN was measured to be 280 nm.

Al, Ga)N light emitting diodes (LEDs), emitting over a large spectral range from 360 nm (GaN) down to 210 nm (AlN), have been successfully fabricated over the last decade. Clear advantages compared to the traditional mercury lamp technology (e.g. compactness, low-power operation, lifetime) have been demonstrated. However, LED efficiencies still need to be improved. The main problems are related to the structural quality and the p-type doping efficiency of (Al, Ga) N. Among the current approaches, GaN nanostructures, which confine carriers along both the growth direction and the growth plane, are seen as a solution for improving the radiative recombination efficiency by strongly reducing the impact of surrounding defects. Our approach, based on a 2D - 3D growth mode transition in molecular beam epitaxy, can lead to the spontaneous formation of GaN nanostructures on (Al, Ga)N over a broad range of Al compositions. Furthermore, the versatility of the process makes it possible to fabricate nanostructures on both (0001) oriented "polar" and (11 (2) over bar 2) oriented "semipolar" materials. We show that the change in the crystal orientation has a strong impact on the morphological and optical properties of the nanostructures. The influence of growth conditions are also investigated by combining microscopy (SEM, TEM) and photoluminescence techniques. Finally, their potential as UV emitters will be discussed and the performances of GaN / (Al, Ga) N nanostructure-based LED demonstrators are presented.

We compare the optical properties of GaN/Al0.15Ga0.85N multiple quantum wells grown on an m-plane (10-10) oriented GaN substrate with those of (1-101)-oriented GaN/Al0.15Ga0.85N multiple quantum wells grown by metal-organic chemical vapor deposition on a patterned (001) 7°-off oriented silicon substrate. The optical properties are studied in 8K-300K temperature range. They reveal strong in-plane optical anisotropies as predicted by group theory. Polarized time resolved temperature- dependent photoluminescence experiments are performed providing access to the relative contributions of the non-radiative and radiative recombination processes. We deduce the variation of the radiative decay time with temperature in the two polarizations. A global comparison of the light emission efficiency in both samples is finally addressed and brought in agreement with the predictions of k.p calculations.