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A thermodynamic equilibrium description of the high‐temperature (150–250 °C) steady‐state behavior of light‐induced defects in amorphous silicon is presented. The entropy and enthalpy of dangling‐bond formation are quantified. In contrast to the behavior of vacancies in single‐crystalline silicon the creation of the dangling‐bond defect in amorphous silicon produces negative entropy and enthalpy changes indicating that lattice relaxations contribute to the free‐energy changes. Over the temperature range examined, the creation of dangling bonds lowers the free energy due to the relatively large negative enthalpy change. Practical issues such as the estimation of the saturated dangling‐bond density resulting from given illumination level at temperatures too low to experimentally observe true saturation are also considered.

Hot-electron energy relaxation time is deduced for Ga-doped ZnO epitaxial layers from pulsed hot-electron noise measurements at room temperature. The relaxation time increases from ∼0.17 ps to ∼1.8 ps when the electron density increases from 1.4 × 1017 cm−3 to 1.3 × 1020 cm−3. A local minimum is resolved near an electron density of 1.4 × 1019 cm−3. The longest energy relaxation time (1.8 ps), observed at the highest electron density, is in good agreement with the published values obtained by optical time-resolved luminescence and absorption experiments. Monte Carlo simulations provide a qualitative interpretation of our observations if hot-phonon accumulation is taken into account. The local minimum of the electron energy relaxation time is explained by the ultrafast plasmon-assisted decay of hot phonons in the vicinity of the plasmon–LO-phonon resonance.

Thermally induced reactions in TiN/Al–Cu/TiN have been investigated. It is observed that the amount of the reactions is different at the two interfaces between Al–Cu and TiN. While there is minimal reaction between Al–Cu and the TiN overlayer, the reaction between Al–Cu and the TiN underlayer increases the sheet resistance of Al–Cu by as much as 15%. It is further shown that the asymmetric reactions are most likely caused by the different degree of (111) texture of TiN grown on amorphous SiO2 and textured, polycrystalline Al–Cu.

We report a resistive switching memory structure based on silicon wafers by employing both materials and processing fully compatible with complementary metal-oxide semiconductor technology. A SiOx nanolayer was fabricated by direct plasma-oxidation of silicon wafers at room-temperature. Resistive switching behaviors were investigated on both p- and n-Si wafers, whereas self-rectifying effect was obtained in the Cu/SiOx/n-Si structure at low-resistance state. The self-rectifying effect was explained by formation of the Schottky barrier between the as-formed Cu filament and the n-Si. These results suggest a convenient and cost-efficient technical-route to develop high-density resistive switching memory for nowadays Si-based semiconductor industry.

Resistive switching mechanism of Ti/HfOx/Pt memory devices was studied using X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy images. Spatial distributions of valence of Hf demonstrated that the fraction of Hf4+ increased from Ti/HfOx interface to HfOx/Pt interface in high resistance state (HRS), but it maintained a constant level in low resistance state (LRS). Rupture of oxygen vacancies formed conducting paths occurred near the HfOx/Pt interface. The cross sectional images of active switching region also varied with HRS and LRS. A dynamic model of interface processes was proposed to interpret interfaces migration of oxygen vacancies near both the top and bottom electrodes.

We report microstructural characterization of heavily Ga-doped ZnO (GZO) thin films on GaN and sapphire by aberration-corrected scanning transmission electron microscopy. Growth under oxygen-rich and metal-rich growth conditions leads to changes in the GZO polarity and different extended defects. For GZO layers on sapphire, the primary extended defects are voids, inversion domain boundaries, and low-angle grain boundaries. Ga doping of ZnO grown under metal-rich conditions causes a switch from pure oxygen polarity to mixed oxygen and zinc polarity in small domains. Electron energy loss spectroscopy and energy dispersive spectroscopy spectrum imaging show that Ga is homogeneous, but other residual impurities tend to accumulate at the GZO surface and at extended defects. GZO grown on GaN on c-plane sapphire has Zn polarity and no voids. There are misfit dislocations at the interfaces between GZO and an undoped ZnO buffer layer and at the buffer/GaN interface. Low-angle grain boundaries are the only threadin...

Electrical behavior of Sb in ZnO:Sb layers doped in a wide concentration range was studied using temperature dependent Hall effect measurements. The layers were grown by plasma-enhanced molecular beam epitaxy, and the Sb concentration was changed by varying the Sb flux, resulting in electron concentrations in the range of 1016 to nearly 1020 cm−3. Upon annealing, the electron concentration increased slightly and more notable was that the electron mobility significantly improved, reaching a room-temperature value of 110 cm2/V s and a low-temperature value of 145 cm2/V s, close to the maximum of ∼155 cm2/V s set by ionized impurity scattering. Hall data and structural data suggest that Sb predominantly occupies Zn sublattice positions and acts as a shallow donor in the whole concentration range studied. In the layers with high Sb content (∼1 at. %), acceptor-type compensating defects (possibly Sb on oxygen sites and/or point-defect complexes involving SbO) are formed. The increase of electron concentration with increasing oxygen pressure and the increase in ZnO:Sb lattice parameter at high Sb concentrations suggest that acceptors involving SbO rather than SbZn-2VZn complexes are responsible for the compensation of the donors.

We report on the mechanisms governing electron transport using a comprehensive set of ZnO layers heavily doped with Ga (GZO) grown by plasma-enhanced molecular-beam epitaxy on a-plane sapphire substrates with varying oxygen-to-metal ratios and Ga fluxes. The analyses were conducted by temperature dependent Hall measurements which were supported by microstructural investigations as well. Highly degenerate GZO layers with n > 5 × 1020 cm−3 grown under metal-rich conditions (reactive oxygen-to-metal ratio

We report a void defect in gallium nitride (GaN) and InGaN, revealed by aberration-corrected scanning transmission electron microscopy (STEM). The voids are pyramids with symmetric hexagonal {0001} base facets and {101¯1} side facets. Each pyramid void has a dislocation at the peak of the pyramid, which continues up along the [0001] growth direction to the surface. Some of the dislocations are hexagonal open core screw dislocations with {101¯0} side facets, varying lateral widths, and varying degrees of hexagonal symmetry. STEM electron energy loss spectroscopy spectrum imaging showed a large C concentration inside the void and on the void surfaces. There is also a larger C concentration in the GaN (or InGaN) below the void than above the void. We propose that inadvertent carbon deposition during metal organic chemical vapor deposition growth acts as a mask, stopping the GaN deposition locally, which in combination with lateral overgrowth, creates a void. Subsequent layers of GaN deposited around the C co...

W-type barium hexaferrite platelets Ba(ZnxCo1−x)2Fe16O27 (0.1 ≤ x ≤ 0.9) were prepared by a chemical coprecipitation route. The results of field-emission scanning electronic microscopy showed that the grains were regular hexagonal platelets with sizes from 0.5 to 1.5 μm. With increasing x, the coercivity decreased, whereas the saturation magnetization increased. Microwave absorption properties were investigated in the frequency range of 8–12 GHz. An optimal reflection loss (−24.8 dB) reached at 10 GHz for x = 0.5 with a thickness of 2 mm. These results indicated that our samples might be a potential candidate for permanent magnets and microwave absorption materials.

We report on the tuning of permittivity and permeability of a ferroelectric/ferromagnetic bilayer structure which can be used as a microwave phase shifter with two degrees of tuning freedom. The structure was prepared by the growth of a yttrium iron garnet (YIG) layer on a gadolinium gallium garnet substrate by liquid phase epitaxy, the growth of a barium strontium titanate (BST) layer on the YIG layer through pulsed laser deposition, and then the fabrication of a coplanar waveguide on the top of BST through e-beam evaporation and trilayer liftoff techniques. The phase shifters exhibit a differential phase shift of 38°/cm at 6 GHz through permittivity tuning under an applied electric field of ∼75 kV/cm and a static magnetic field of 1700 Oe. By tuning the permeability through the applied magnetic field we increase the differential phase shift to 52°/cm and simultaneously obtain a better match to the zero applied electric field condition, resulting in an improvement in the return loss from 22.4 to 24.9 dB....

Dielectric properties of annealed and as-grown ferroelectric Ba0.5Sr0.5TiO3 (BST) grown by pulsed laser deposition on sputtered BST seed layers on strontium titanate (STO) substrates were investigated at microwave frequencies in the realm of tunability of its dielectric constant as well as phase shifters based on this material. The as-grown layers were nearly fully relaxed with measured lattice parameters nearly identical to those of bulk BST. The tuning of the relative dielectric constant (∼1750 at zero bias at 10 GHz) of the annealed BST was found to be as high as 59% and 56% at 10 and 19 GHz, respectively. The analysis of the loss in the BST results in a measured tan δ of 0.02 for the annealed as well as the unannealed films at a frequency of 18 GHz. Phase shifters also exhibited high tuning with differential phase shift figures of merit of 35 and 55°/dB at a field of 60 kV/cm at 10 and 19 GHz, respectively. Serendipitously, most of the tuning occurs at low fields, and thus we propose a new figure of m...

The structural and magnetic properties of NiCo∕(Ni,Co)O bilayers were investigated. X-ray diffractometry results have shown that the top NiCo layer consisted of a fcc NiCo phase. The bilayer bottom was either a pure (Ni,Co)O or a composite [NiCo+(Ni,Co)O] phase, depending on the percent of O2∕Ar ratio used during deposition. A double-shifted hysteresis loop exhibiting components that were from positive or negative coupling was observed in the NiCo∕(Ni,Co)O (8%O2∕Ar) bilayers. The microstructural changes, which result from a combination of deposition oxygen content and the ion-beam bombardment, will result in the unusual exchange bias behavior.

The longitudinal magnetic-field dependence of quantized spin waves in ordered permalloy nanowire arrays in two dimensions (2D) has been studied by Brillouin spectroscopy. The results were analyzed on the basis of collective spin waves in a hexagonal 2D nanowire array and compared with the results obtained from an analysis of spin waves in an isolated wire. It is found that only the lowest-frequency spin-wave mode of an isolated nanowire is marginally influenced by the presence of neighboring nanowires. These findings are significant for the theoretical understanding and the future technological utilization of magnetic nanowires.