V. Sallet

Electrical activity of nitrogen acceptors in ZnO films grown by metalorganic vapor phase epitaxy

The electrical activity of nitrogen as an acceptor in ZnO has been investigated in two ways. First, nitrogen was introduced by means of diallylamine during metalorganic vapor phase epitaxy (MOVPE) yielding incorporation of nitrogen in the range 1016–1021 cm−3. This led to significant compensation of the natural donors with a minimum electron concentration of 5×1014 cm−3. Second, diffusion of nitrogen was carried out on undoped MOVPE layers under high pressure conditions stemming from the decomposition of NH4NO3. Conversion to p-type conductivity was observed in a systematic way with measured hole concentrations up to 6.5×1017 cm−3.

Effects of intentionally introduced hydrogen on the electrical properties of ZnO layers grown by metalorganic chemical vapor deposition

Unintentionally doped ZnO layers grown epitaxially on a sapphire substrate have been exposed either to a hydrogen or deuterium plasma. Secondary ion mass spectroscopy measurements performed subsequently showed a rapid diffusion of hydrogen in these layers. Furthermore, the presence of hydrogen in the ZnO samples is found to be responsible for nearly a factor of 3 increase in the free electron concentration. This effect is attributed to the hydrogen passivation of compensating acceptor impurities present in the as-grown ZnO layers.

Investigations on GaInNAsSb quinary alloy for 1.5 μm laser emission on GaAs

GaInNAsSb quantum wells grown by molecular-beam epitaxy on GaAs substrates were investigated. Intricate incorporation mechanisms of the constituents in this quinary alloy were seen. In highly strained indium-rich alloys, antimony incorporation is strongly reduced, and a beneficial surfactant effect is observed. Due to this effect, high structural quality is preserved even for an uncompensated 2.67% strained multiquantum-well structure. Narrow luminescence linewidth (35 meV) could be achieved near 1.55 μm wavelength with these quantum wells. Laser emission is demonstrated at 1.50 μm with threshold current density of 3.5 kA/cm2.

Strain-Fields Effects and Reversal of the Nature of the Fundamental Valence Band of ZnO Epilayers.

We examine the influence of strain fields in ZnO epilayers. We show that a reversal of the nature of the fundamental valence band can be observed similarily to what was reported in GaN epilayers.

Some aspects of the MOCVD growth of ZnO on sapphire using tert-butanol

The growth of ZnO on (0001) sapphire substrates using metalorganic chemical vapor deposition is reported. Diethylzinc and tertiarybutanol were used, respectively, as zinc and oxygen sources. Growth conditions are detailed such as the substrate temperature and the precursors partial pressures. The influence of the cleanness state of the MOCVD silica reactor is emphasized, since it modifies both layer quality and crystalline orientation, and since it also affects growth process steps like sapphire thermal treatment and buffer layer deposition. ZnO epitaxial layers are characterised by scanning electron microscopy (SEM) to assess the surface orientation and morphology, X-ray diffraction (XRD) and photoluminescence (PL). This last technique demonstrates the high optical quality of the ZnO epilayers.

Metal organic chemical vapor deposition growth and luminescence of ZnO micro- and nanowires

One dimensional (1D) ZnO heterostructures were deposited on C-plane sapphire using metal organic chemical vapor deposition at atmospheric pressure. Both catalyst-assisted and catalyst-free processes were investigated. In this latter case, growth parameters such as the substrate temperature, the oxygen/zinc ratio, or the carrier gas nature were varied in order to observe the modification of the film morphology. Different 1D shapes were produced, including rods, tubes, and needles, and were observed by scanning electron microscopy. Photoluminescence spectra reveal sharp excitonic transitions, and cathodoluminescence signals recorded along a ZnO conical needle exhibit a blueshift from the base to the top. The vapor-liquid-solid growth of ZnO nanowires using gold droplets was also successful.

Floor free 10-Gb/s transmission with directly modulated GaInNAs-GaAs 1.35-/spl mu/m laser for metropolitan applications

Among the new semiconductor materials for telecom devices, the GaInNAs-GaAs structure presents interesting properties for low-cost applications, like high differential gain and high T/sub 0/. Another key aspect of the performance is the behavior of the GaInNAs-GaAs based lasers under high bit rate direct modulation. Here, we demonstrate the dynamic capabilities of GaInNAs-GaAs three-quantum-well ridge structure through 2.5-Gb/s directly modulated laser emission and transmission on standard fiber, in the temperature range 25/spl deg/C-85/spl deg/C. Besides transmission is demonstrated up to 10 Gb/s at 25/spl deg/C on the same fiber, without penalty and bit-error-rate floor.

Quantitative analysis of doped/undoped ZnO nanomaterials using laser assisted atom probe tomography: Influence of the analysis parameters

In the last decade, atom probe tomography has become a powerful tool to investigate semiconductor and insulator nanomaterials in microelectronics, spintronics, and optoelectronics. In this paper, we report an investigation of zinc oxide nanostructures using atom probe tomography. We observed that the chemical composition of zinc oxide is strongly dependent on the analysis parameters used for atom probe experiments. It was observed that at high laser pulse energies, the electric field at the specimen surface is strongly dependent on the crystallographic directions. This dependence leads to an inhomogeneous field evaporation of the surface atoms, resulting in unreliable measurements. We show that the laser pulse energy has to be well tuned to obtain reliable quantitative chemical composition measurements of undoped and doped ZnO nanomaterials.

Characterizations of Ohmic and Schottky-behaving contacts of a single ZnO nanowire

Current-voltage and Kelvin probe force microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either Ohmic or diode-like. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality Ohmic contacts (linear I-V behavior) or non-linear (diode-like) contacts were obtained. Current-voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to investigate their behavior. A clear correlation could be established between the I-V curve, the electrical potential profile along the device and the nanowire geometry. Some arguments supporting this behavior are given based on technological issues and on depletion region extension. This work will help to better understand the electrical behavior of Ohmic contacts on single ZnO nanowires, for future applications in nanoscale field-effect transistors and nano-photodetectors.

MOCVD growth of ZnO on sapphire using tert-butanol

The growth of ZnO on (0001) sapphire substrates using metalorganic chemical vapor deposition (MOCVD) is investigated. Usual growth conditions are detailed. In addition, a particular attention is paid to the cleanness state of the MOCVD reactor. ZnO epilayers are characterized by scanning electron microscopy, X-ray diffraction and photoluminescence.