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The authors report on the fabrication and characterization of thin film transistors that use sputter deposited amorphous indium zinc oxide both for the channel and source-drain metallizations in a gate-down configuration. The channel and source-drain layers were deposited from a single In2O3–10wt%ZnO ceramic target using dc magnetron sputtering onto an unheated substrate. The carrier densities in the channel (2.1×1017∕cm3) and source/drain regions (3.3×1020∕cm3) were adjusted by changing the reactive oxygen content in the sputter chamber during deposition. The resulting transistors operate as depletion mode n-channel field effect devices with saturation mobility of 20cm2∕Vs and on/off current ratio of 108.

Deposition of tin-doped–indium-oxide (ITO) on unheated substrates via low energy processes such as electron-beam deposition can result in the formation of amorphous films. The amorphous-to-crystalline transformation was studied in this system using in situ resistivity, time resolved reflectivity, glancing incidence angle x-ray diffraction, and transmission electron microscopy. The resistivity of 180 nm thick In2O3(9.9 wt. %SnO2) was monitored during isothermal anneals at 125, 135, 145, and 165 °C. The dependence of the resistance on the volume fraction of crystalline phase was established using glancing incidence angle x-ray diffraction and a general two phase resistivity model for this system was developed. These studies show that, upon annealing, as-deposited amorphous ITO undergoes both a structural relaxation and crystallization. Structural relaxation of the amorphous material includes local ordering that increases the ionized vacancy concentration which, in turn, increases the carrier density in the material. Kinetic growth parameters were extracted from the data, which reveal that the relaxation of the amorphous structure occurs via a process that obeys a first order reaction rate law, while crystallization occurs via classical nucleation and growth with a growth mode parameter that is consistent with two- to three-dimensional transformation geometry. Both the relaxation and crystallization processes have an activation energy of approximately 1.3±0.2 eV. Time resolved reflectivity analysis of the electron beam deposited ITO reveals that there is a sharp and monotonic decrease in reflectivity during the anneal of the sample which is associated with the amorphous relaxation process.

Teleomorph: Venturia inaequalis Cooke (Wint.); Kingdom Fungi; Phylum Ascomycota; Subphylum Euascomycota; Class Dothideomycetes; Family Venturiaceae; genus Venturia; species inaequalis. Anamorph: Fusicladium pomi (Fr.) Lind or Spilocaea pomi (Fr.). LIFE CYCLE: V. inaequalis is a hemibiotroph and overwinters as pseudothecia (sexual fruiting bodies) following a phase of saprobic growth in fallen leaf tissues. The primary inoculum consists of ascospores, which germinate and penetrate the cuticle. Stromata are formed above the epidermal cells but do not penetrate them. Cell wall-degrading enzymes are only produced late in the infection cycle, raising the as yet unanswered question as to how V. inaequalis gains nutrients from the host. Conidia (secondary inoculum) arise from the upper surface of the stromata, and are produced throughout the growing season, initiating multiple rounds of infection. VENTURIA INAEQUALIS AS A MODEL PATHOGEN OF A WOODY HOST: V. inaequalis can be cultured and is amenable to crossing in vitro, enabling map-based cloning strategies. It can be transformed readily, and functional analyses can be conducted by gene silencing. Expressed sequence tag collections are available to aid in gene identification. These will be complemented by the whole genome sequence, which, in turn, will contribute to the comparative analysis of different races of V. inaequalis and plant pathogens within the Dothideomycetes.

Stress evolution during molecular-beam epitaxy of AIN films was monitored with in situ curvature measurements. Changes in the growth rate produced large stress variations, with more tensile stress observed at higher growth rates. For example, at a growth temperature of 750°C the instantaneous steady-state stress in films with similar grain sizes varied from −0.15GPa at a growth rate of 90nm∕h, to approximately 1.0GPa at a growth rate of 300nm∕h. To explain these results, we develop a kinetic model of stress evolution that describes both tensile and compressive mechanisms. The tensile component is based on a mechanism which is proposed here as an inherent feature of grain-boundary formation. The compressive component is based on our recent model of atom insertion, driven by the excess chemical potential of surface adatoms that is created by the growth flux. The combined model predicts that the stress is largely governed by the competition between tensile and compressive mechanisms, which can be conveniently described with a single parameter, α. The limiting values α→0 and α→+∞ correspond to previous models of compressive and tensile stresses, respectively.

This work characterizes a GaN:Mg on silicon ultraviolet photodetector with a cutoff at 3.3 eV and a responsivity of 12 A/W at 4 V bias for optical intensities on the order of 1 W/m2 and below. A weak photovoltaic response is also reported. The photocurrent is nearly linear versus optical intensity for up to 10 W/m2. The responsivity increases nearly linearly with applied voltage up to 8 V, then the increase slows toward saturation. To explain this high responsivity in a direct gap semiconductor, it is hypothesized that holes are captured at either compensated Mg deep acceptor sites or Mg-related trap/recombination centers, resulting in a greatly prolonged electron free-carrier lifetime.

The optical transitions in undoped, hexagonal GaN layers, grown on Si(111) by molecular beam epitaxy under nitrogen-rich conditions, have been studied by photoluminescence spectroscopy. Several intense excitonic emissions, of free and bound character, are detected as narrow as 1.7 meV at low temperature. The free A, B and C excitons, observed at 3.4786 eV, 3.484 eV and 3.503 eV, respectively, allow the determination of the crystal-field ( cr = 9.9 meV) and spin-orbit ( so = 19.9 meV) splittings. The evolution of their energies with temperature has been analysed with two different fits, the gap shift proportional to T 2 /(T + θ D ) and 1/[exp(θ E /T ) − 1] respectively. Information on the scattering processes is obtained from the peak broadening, which is due to exciton-phonon interactions. Both the free exciton energies and their temperature behaviour agree with those observed in bulk and homoepitaxial GaN, and therefore the studied GaN/Si layers are strain-free. Up to four extrinsic transitions at 3.4755 eV, 3.4714 eV, 3.456 eV and 3.450 eV have also been observed, and their assignment to bound excitons and donor to band transitions is discussed. Finally, a band at 3.41-3.42 eV is attributed to a donor-to-acceptor transition. This interpretation implies the presence of an acceptor lying at 70 meV above the valence band, shallower than those usually employed for p-type doping.

To realize the desired zero-dimensional behavior of a quantum dot ensemble, the ability to fabricate quantum dots with a high packing density and a high degree of size, shape, and spacing uniformity is crucial. Here we report highly ordered InAs nanodot arrays grown by molecular-beam epitaxy on nonlithographically nanopatterned GaAs. Approximately 20 billion dots are grown in a 1cm2 area with the smallest size dispersion ever reported and forming a lateral superlattice in hexagonal dense packing form. These techniques presage a pathway to controlled growth of periodic quantum dot superstructures, which offer macroscopic spatial coherence in the interaction of quantum dots with radiation.