Highly crystalline zinc oxide (ZnO) nanomaterials are synthesized using a seeded growth sol-gel method. In order to control the morphology and the organization of the ZnO nanomaterials, a double hydrophilic block copolymer has been introduced during the seeded growth synthesis: the Polyacrylic acid-Polyacrylamide (PAA-PAM). Depending on the amount of PAA-PAM copolymers, different morphologies were obtained, such as ZnO nanostructured spheres or flat hexagonal crystals. Thus, systematic studies have been done to investigate the influence of the copolymer addition on ZnO nanomaterial morphologies and explain the mechanisms of the morphological modifications.

We report continuous-wave and time-resolved optical spectroscopy of ZnO nanorods and nanowires of varying diameters grown by MOVPE, under varying thermo-dynamical conditions. We discuss the influence of these conditions on the different spectral components. Two families of photoluminescence lines are identified. The first one is related to defect-bound excitons and to their two-electron replica. The second one is correlated to near surface states. The relative intensities of various contributions appear to be strongly dependent on the growth conditions and of the diameter of the nanostructures. Photoluminescence decay time of the different lines has been measured on one of the samples.

We present a k.P theoretical study of the energy band properties of würtzite ZnO/Zn1−xMgxO Quantum Well Heterostructures (QWH) as a function of the alloy composition x in the range x<0.4, and for various well widths. For this purpose, we use a Luttinger-type effective mass model, the 6×6 Rashba–Sheka–Pikus model, to describe the valence bands of these QWH. By using the k.P parameters available in the literature, we have first computed the energy band-structure dispersion of bulk ZnO and we have found good agreement with previous k.P, as well as, ASA-LMPTO results. Then we have computed the valence band dispersion and confinement energies in the range of interest x<0.40 and for various well widths LZ. Good agreement is found with the available pump–probe PL results, for the peak energies of linear absorption for various QWH are closely fitted.

We analyze the low temperature photoluminescence properties of two multi-layer stacking of GaN/AlN quantum dots. We report drastic differences of linewidths between continuous wave and time-resolved photoluminescence experiments. After the pulsed excitation, time-resolved photoluminescence reveals a substantial red shift of the line, which keeps a fairly constant width. In continuous wave experiments, the screening of internal electric fields by accumulation of e-h pairs in quantum dot planes induces a blue-shift. For samples with large number of quantum dot planes an unexpected narrowing of the emission line is observed when the laser intensity is increased. We assign the observed behaviors of energies and linewidths to the contributions of the in-depth decrease of the degree of excitation of the different planes. Our interpretation is supported by the use of a model based on a self-consistent solution of the Schrodinger and Poisson equations within the envelope function approximation.

The composition dependence of the band-gap reduction of GaAs1-xNx grown by molecular beam epitaxy and metal organic vapor phase epitaxy was investigated using transmission, reflection, and low-temperature photoluminescence (PL) spectroscopy for N incorporations ranging from doping concentrations up to x=5 × 10-2. We identified four different regimes of N incorporation with distinctly different band-gap scaling. N-doped GaAs shows sharp PL lines due to N cluster states, but no significant change in the band gap. In the ultradilute region (10-5≤x≤ 1.5 × 10-3) a strong band-gap reduction was observed which scales according to x, irrespective of the local distribution of N atoms in the As sublattice. The same band-gap scaling was observed for ultradilute InGaAsN after corrections for strain and In alloying. In an intermediate compositional region (1.5 × 10-3≤x≤2.5×10-2) ΔEg scales according to x2/3. At higher concentrations (x>2.5 × 10-2) ΔEg weakens due to effects connected with N oversaturation of the As sublattice.

Piezoelectric effects on the optical properties of GaN/AlN quantum dots have been investigated by both continuous-wave and time-resolved photoluminescence (TRPL) measurements. The increase in excitation density in CW-PL leads to a blue shift of the transition energy. The TRPL measurements reveal a very large blue-shift (0.6 eV) of the PL peak energy, which reduces with time delay in a complex way, due to the strong transition-energy dependence of the carrier recombination time. The results are discussed in terms of respective roles played by the population of excited levels and by the screening of internal electric fields by accumulation of electron-hole dipoles in the quantum boxes. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.