Temperature dependence of contact resistance for Au-Ti-Pd<Subscript>2</Subscript>Si-<Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>-Si ohmic contacts subjected to microwave irradiation

Based on a theoretical analysis of the temperature dependence of the contact resistance R _c for an Au-Ti-Pd₂Si-n ⁺-Si ohmic contact, a current-transfer mechanism explaining the experimentally observed increase in R _c in the temperature range 100–380 K is proposed. It is shown that microwave treatment of such contacts results in a decrease in the spread of R _c over the wafer and a decrease in the value of R _c whilst retaining an increase in R _c in the temperatures range 100–380 K.     

Al ohmic contacts to HCI-treated Mg<Subscript>x</Subscript>Zn<Subscript>1−x</Subscript>O

The Al nonalloyed ohmic contacts were fabricated on Mg_xZn_1−xO (0≤x≤0.2) thin films. HCl surface treatment significantly reduced the specific contact resistances to value around 10⁻⁴ Ω cm². X-ray photoelectron spectroscopy (XPS) analysis revealed that the HCl treatment increased the oxygen vacancy density and introduced chlorine to the semiconductor surface, resulting in a thin conductive layer and thus reduced specific contact resistance. A subsequent oxygen plasma treatment reduced the oxygen vacancy density, and correspondingly increased the specific contact resistance. Al-ZnO contacts were insensitive to the HCl treatment, due to the formation of a highly conductive Al-doped thin interface layer.     

Effect of Ar<Superscript>+</Superscript> Radiofrequency Plasma Treatment Conditions on the Interfacial Adhesion Energy Between Atomic-Layer-Deposited Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Cu Thin Films in Embedded Capacitors

The effects of Ar⁺ radiofrequency (RF) plasma pretreatment conditions on the interfacial adhesion energy of a Cu/Cr/Al₂O₃ system were investigated for thin-film capacitors in embedded printed circuit board applications. The interfacial adhesion energy was evaluated from 90 deg peel tests by calculating the plastic deformation energy of peeled metal films from the energy balance relationship during the steady-state peeling process. The interfacial adhesion energy was fivefold higher after RF plasma pretreatment of the surface of 50-nm-thick Al₂O₃ prepared by atomic layer deposition. Atomic force microscopy, Auger electron spectroscopy, and x-ray photoemission spectroscopy results clearly reveal that this increase can be attributed to both mechanical interlocking and chemical bonding effects.     

Formation of Precipitates in Si Implanted with <Superscript>64</Superscript>Zn<Superscript>+</Superscript> and <Superscript>16</Superscript>O<Superscript>+</Superscript> Ions

The results of studying the surface Si layer and precipitate formation in CZ n-Si(100) samples sequentially implanted with ⁶⁴Zn⁺ ions with a dose of 5 × 10¹⁶ cm² and energy of 100 keV and ¹⁶O⁺ ions with the same dose but an energy of 33 keV at room temperature so that their projection paths R_p = 70 nm would coincide are presented. The post-implantation samples are annealed for 1 h in an inert Ar medium in the temperature range of 400–900°C with a step of 100°C. The profiles of the implanted impurities are studied by time-of-flight secondary ion mass spectrometry. The Si surface is visualized using a scanning electron microscope, while the near-surface layer is visualized with the help of maps of elements formed by Auger electron spectroscopy with profiling over depth. The ZnO(002) texture is formed in an amorphized Si layer after the implantation of Zn and O ions. ZnO(102) crystallites of 5 nm in size are found in a recrystallized single-crystalline Si layer after annealing in Ar at 700°C.     

Effect of Proton Irradiation on Interface State Density in Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/GaN and Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/MgO/GaN Diodes

Proton irradiation of Sc₂O₃/GaN and Sc₂O₃/MgO/GaN metal-oxide semiconductor diodes was performed at two energies, 10 MeV and 40 MeV, and total fluences of 5 × 10⁹ cm⁻², corresponding to 10 years in low-earth orbit. The proton damage causes a decrease in forward breakdown voltage and a flat-band voltage shift in the capacitance-voltage characteristics, indicating a change in fixed oxide charge and damage to the dielectric. The interface state densities after irradiation increased from 5.9 × 10¹¹ cm⁻² to 1.03 × 10¹² cm⁻² in Sc₂O₃/GaN diodes and from 2.33 × 10¹¹ to 5.3 × 10¹¹ cm⁻² in Sc₂O₃/MgO/GaN diodes. Postannealing at 400°C in forming gas recovered most of the original characteristics but did increase the interfacial roughness.     

Dielectric properties of low loss Ba<Subscript>6−3x</Subscript>Nd<Subscript>8+2x</Subscript>Ti<Subscript>18</Subscript>O<Subscript>54</Subscript> thin films prepared by pulsed laser deposition for microwave applications

Ba_6−3xNd_8+2xTi₁₈O₅₄ with x=0.25 (BNT-0.25, or simply, BNT) dielectric thin films with a thickness of 320 nm have been prepared on Pt-coated silicon substrates by pulsed laser deposition (PLD) at the substrate temperature of 650°C in 20 Pa oxygen ambient. X-ray analysis showed that the as-deposited films are amorphous and the films remain amorphous after a postannealing at 750°C for 30 min. The dielectric constant of the BNT films has been determined to be about 80 with a low loss tan δ of about 0.006 at 1 MHz. The capacitance-voltage (C-V), capacitance-frequency, and capacitance-temperature characteristics of a BNT capacitor with Pt top electrode were measured. A low leakage-current density of 4×10⁻⁶ A/cm² at 6 V was measured, and a preliminary discussion of the leakage-current mechanism is also given. It is proposed that amorphous BNT-0.25 thin films will be a potential dielectric material for microwave applications.     

Uniform Cr<Superscript>2+</Superscript> doping of physical vapor transport grown CdS<Subscript>x</Subscript>Se<Subscript>1−x</Subscript> crystals

The Cr²⁺ doped CdS_0.8Se_0.2 crystals were grown by the vertical, self-seeded, physical vapor transport (PVT) technique. Good quality, crack- and inclusion-free single crystals were grown with an average Cr²⁺ concentration of 5 × 10¹⁸ cm⁻³. Different source-to-tip distances were used to improve the segregation coefficient (Cr_crystal/Cr_source) of the grown crystals. It was observed that lowering the source-to-tip distance increases the segregation coefficient dramatically. With a 2-cm source-to-tip distance, good quality crystals were grown with uniform Cr²⁺ concentration throughout the ingot. The segregation coefficient was found to be ∼0.85. The composition of the crystals was also found to be fairly uniform along the length and across the diameter.     

On a two-layer Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> dielectric mask for low-resistance ohmic contacts to AlGaN/GaN HEMTs

The fabrication of a two-layer Si₃N₄/SiO₂ dielectric mask and features of its application in the technology of non-fired epitaxially grown ohmic contacts for high-power HEMTs on AlGaN/GaN heterostructures are described. The proposed Si₃N₄/SiO₂ mask allows the selective epitaxial growth of heavily doped ohmic contacts by nitride molecular-beam epitaxy and the fabrication of non-fired ohmic contacts with a resistance of 0.15–0.2 Ω mm and a smooth surface and edge morphology.     

Vanadium-based ohmic contacts to n-type Al<Subscript>0.6</Subscript>Ga<Subscript>0.4</Subscript>N

Four vanadium-based contacts to n-type Al_0.6Ga_0.4N were compared in this work. Both V/Al/Pd/Au and V/Al/V/Au contacts with optimized layer thicknesses provided lower specific-contact resistances than did the previously reported V/Al/Pt/Au ohmic contact. Specific contact resistances of the V/Al/Pd/Au (15 nm/85 nm/20 nm/95 nm) and V/Al/V/Au (15 nm/85 nm/20 nm/95 nm) contacts were 3×10⁻⁶ Ω·cm² and 4×10⁻⁶ Ω·cm², respectively. On the other hand, an analogous V/Al/Mo/Au contact never became ohmic, even after it was annealed at 900°C for 30 sec. Compared to the V/Al/Pd/Au contact, the V/Al/V/Au contact required a less severe annealing condition (30 sec at 700°C instead of 850°C). The V/Al/V/Au contact also provided a smoother surface, with a root-mean-square (RMS) roughness of 39 nm.     

Radiative recombination in Ge<Superscript>+</Superscript>-implanted SiO<Subscript>2</Subscript> films annealed under hydrostatic pressure

Photoluminescence (PL) spectra and PL excitation spectra were recorded at room temperature from SiO₂ films implanted with Ge⁺ ions and annealed at temperature T _a =450–1100°C under hydrostatic pressure P=12 kbar. The emergence of features in the violet and green bands of the PL and PL excitation spectra correlates with the formation of hydrostatically strained Ge nanocrystals. The shift of the PL bands to higher energies, which occurs as the annealing temperature is raised to T _a ≥800°C, can be attributed to a shift of the energy levels related to the radiative recombination centers, which is caused by the increasing deformation potential. The observed PL is accounted for by the enhanced probability of direct radiative transitions in Ge nanocrystals with an X-like conduction band.     

Optical Properties of K<Subscript>2</Subscript>O-Li<Subscript>2</Subscript>O-WO<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Glasses: Evidence of Mixed Alkali Effect

Glass with compositions xK₂O-(30 ? x)Li₂O-10WO₃-60B₂O₃ for 0 ≤ x ≤ 30 mol.% have been prepared using the normal melt quenching technique. The optical reflection and absorption spectra were recorded at room temperature in the wavelength range 300–800 nm. From the absorption edge studies, the values of the optical band gap (E _opt) and Urbach energy (ΔE) have been evaluated. The values of E _opt and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple Di-Domenico model.     

The Effects of Heat Treatment on the Crystallinity and Luminescence Properties of YInGe<Subscript>2</Subscript>O<Subscript>7</Subscript> Doped with Eu<Superscript>3+</Superscript> Ions

Yttrium indium germanate, YInGe₂O₇, doped with Eu³⁺ ions was synthesized by a solid-state reaction using a vibrating mill with metal oxides. The compound was characterized and its optical properties were investigated. The yielded powders were heated at various temperatures from 1100°C to 1400°C in air for 10 h. The X-ray diffraction profiles showed that all peaks could be attributed to the monoclinic YInGe₂O₇ phase at the various calcination temperatures for YInGe₂O₇ doped with 5 mol.% Eu³⁺ ions. A second phase of In₂O₃ was observed in the X-ray powder diffractometry pattern when the calcination temperature was over 1200°C. Scanning electron microscopy showed that the particle sizes increased significantly with increasing calcination temperature. The calcined powders emitted a reddish luminescence centered at 611 nm under excitation of 393 nm due to the electric dipole transition ⁵D₀ → ⁷F₂. Powders fired at 1200°C were found to have the maximum photoluminescent intensity for YInGe₂O₇ doped with 5 mol.% Eu³⁺ ions. Furthermore, the existence of the second phase caused the decay time to decrease with increasing calcination temperature.     

Structure and dielectric properties of Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>ZnTi<Subscript>7</Subscript>O<Subscript>16</Subscript> hollandite ceramics

Hollandite-type Ba_1−xSr_xZnTi₇O₁₆ (x=0, 0.2, 0.4, 0.6, 0.8, and 1) ceramics have been synthesized by the conventional solid-state ceramic route. The phase purity and microstructure of these compositions have been characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis shows that an increase in strontium concentration in the A-site causes pairing of vacant tunnel sites, and hence the structure becomes unstable due to the collapse of the tunnel walls. The dielectric properties such as dielectric constant (ε_r), loss tangent (tan δ), and temperature variation of dielectric constant (τε_r) have been measured up to the 13 MHz region. The present study shows that zinc hollandites have relatively high dielectric constant and low loss tangent. The temperature variation of dielectric constant studies reveal that Ba-rich compositions have high positive τε_r and Sr-rich compositions have high negative τε_r in the 0–100°C region. Proper tailor making of these compositions has been attempted to arrive at near-zero temperature variation of the dielectric constant.     

Kinetics of polarization current in a Pb<Subscript>3</Subscript>O<Subscript>4</Subscript> wide-gap photoconductor

The results of the study of isothermal polarization of Pb₃O₄ high-resistivity semiconductor layers in a dc electric field of various intensities with measurements without and with illumination are presented. To interpret the data obtained, the relay mechanism of charge transport over local states in the band gap is introduced. The values of the parameters describing the relaxation phenomena such as contact capacitance, width of the charge accumulation region, and effective charge mobility are obtained.     

Electrical properties of Zinc-Tin diarsenide (ZnSnAs<Subscript>2</Subscript>) irradiated with H<Superscript>+</Superscript> ions

The results of studying the electrical properties and isochronous annealing of p-ZnSnAs₂ irradiated with H⁺ ions (energy E = 5 MeV, dose D = 2 × 10¹⁶ cm^?2) are reported. The limiting electrical characteristics of irradiated material (the Hall coefficient R _H (D)_lim ≈ ?4 × 10³ cm³ C^?1, conductivity σ (D)_lim ≈ 2.9 × 10^?2 Ω^?1 cm^?1, and the Fermi level position F _lim ≈ 0.58 eV above the valence-band top at 300 K) are determined. The energy position of the “neutral” point for the ZnSnAs₂ compound is calculated.     

A Single-Composition Trichromatic White-Light-Emitting Phosphor Based on Sr<Subscript>8</Subscript>ZnY(PO<Subscript>4</Subscript>)<Subscript>7</Subscript> Coactivated with Ce<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, and Mn<Superscript>2+</Superscript>

Ce³⁺/Tb³⁺/Mn²⁺-codoped Sr₈ZnY(PO₄)₇ (SZYP) white-emitting phosphors have been synthesized via solid-state reaction technology. The overlapping spectra between the excitation bands of Mn²⁺ and Tb³⁺ ions and the emission band of Ce³⁺ suggest that Ce³⁺ → Mn²⁺ and Ce³⁺ → Tb³⁺ energy transfer occurs. The emission hues exhibited by Ce³⁺/Tb³⁺- and Ce³⁺/Mn²⁺-codoped phosphors could be modulated from bluish to greenish region and from bluish to reddish region by simply adjusting the relative content of Ce³⁺/Tb³⁺ and Ce³⁺/Mn²⁺, respectively. SZYP:Ce³⁺,Tb³⁺,Mn²⁺ samples exhibited three dominant bands at 410 nm, 545 nm, and 600 nm, attributable to electronic transitions of Ce³⁺, Tb³⁺, and Mn²⁺ ions, respectively. Thus, color-tunable emission was achieved by accurately modulating the concentrations of Ce³⁺, Tb³⁺, and Mn²⁺ ions. SZYP:0.05Ce³⁺,0.11Mn²⁺,0.11Tb³⁺ was found to be an ideal white-light-emitting phosphor with color coordinates of (0.34, 0.33) and correlated color temperature of about 5144.83 K. The results indicate that Ce³⁺/Tb³⁺/Mn²⁺ -tridoped SZYP phosphors are potential single-component white-emitting candidates for application in ultraviolet- and white-light-emitting diodes.     

Er<Subscript>2</Subscript>O<Subscript>3</Subscript> for high-gain waveguide amplifiers

Following the demonstration of room-temperature luminescence, Er₂O₃ has been explored as a high-gain medium for ultra-compact waveguide amplifiers. With sputtered and annealed films, we measure three radiative lifetimes (7 ms, 0.8 ms, and 0.5 ms) and upconversion coefficients at 4.2 K. We have correlated these measurements with three crystalline phases: the thermodynamically stable bcc phase and the metastable fcc and hcp phases. The 7-ms lifetime is correlated with the fcc phase, implying the metastable crystal state has a profound influence on inhibiting upconversion interaction between neighbor Er atoms. Measurements indicate optical gain >3 dB/cm is possible.     

Conduction Mechanisms in Multiferroic Multilayer BaTiO<Subscript>3</Subscript>/NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/BaTiO<Subscript>3</Subscript> Memristors

Memristive devices and materials are extensively studied as they offer diverse properties and applications in digital, analog and bio-inspired circuits. In this paper, we present an important class of memristors, multiferroic memristors, which are composed of multiferroic multilayer BaTiO₃/NiFe₂O₄/BaTiO₃ thin films, fabricated by a spin-coating deposition technique on platinized Si wafers. This cost-effective device shows symmetric and reproducible current–voltage characteristics for the actuating voltage amplitude of ±10 V. The origin of the conduction mechanism was investigated by measuring the electrical response in different voltage and temperature conditions. The results indicate the existence of two mechanisms: thermionic emission and Fowler–Nordheim tunnelling, which alternate with actuating voltage amplitude and operating temperature.     

Fabrication and Characterization of Pb(Zr<Subscript>0.53</Subscript>,Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>-Pb(Nb<Subscript>1/3</Subscript>,Zn<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> Thin Films on Cantilever Stacks

0.9Pb(Zr_0.53,Ti_0.47)O₃-0.1Pb(Zn_1/3,Nb_2/3)O₃ (PZT–PZN) thin films and integrated cantilevers have been fabricated. The PZT–PZN films were deposited on SiO₂/Si or SiO₂/Si₃N₄/SiO₂/poly-Si/Si membranes capped with a sol–gel-derived ZrO₂ buffer layer. It is found that the membrane layer stack, lead content, existence of a template layer of PbTiO₃ (PT), and ramp rate during film crystallization are critical for obtaining large-grained, single-phase PZT–PZN films on the ZrO₂ surface. By controlling these parameters, the electrical properties of the PZT–PZN films, their microstructure, and phase purity were significantly improved. PZT–PZN films with a dielectric constant of 700 to 920 were obtained, depending on the underlying stack structure.     

Memory Effect of Metal-Insulator-Silicon Capacitor with HfO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Multilayer and Hafnium Nitride Gate

Metal-insulator-silicon capacitors have been fabricated using novel insulators of SiO₂/HfO₂-Al₂O₃-HfO₂ (HAH)/Al₂O₃ and metallic HfN gate, exhibiting a program-erasable characteristic. The memory capacitor presents a large memory window of 2.4 V under +12 V program/–14 V erase for 10 ms, no erase saturation, and sufficient electron- and hole-trapping efficiencies such as an electron density of ∼7 × 10¹² cm^–2 under 13 V program for 0.5 ms and a hole density of ∼4 × 10¹² cm^–2 under –12 V erase for 0.5 ms. The observed properties are attributed to the introduction of high permittivity atomic-layer-deposited HAH/Al₂O₃ as well as high work function HfN gate. The related mechanism is addressed accordingly.