ECS Journal of Solid State Science and Technology

Biosensor research has been addressed as an interested field recently. Within different kinds of developed biosensing technologies, field-effect transistor (FET) based biosensors stand out due to their attractive features, such as ultra-sensitivity detection, mass-production capability, and low-cost manufacturing. To promote understandings of the FET based biosensing technology, in this review, its sensing mechanism is introduced, as well as major FET-based biosensing devices: ion sensitive field-effect transistor (ISFET), silicon nanowire, organic FET, graphene FET, and compound-semiconductor FET. In addition to FET-based biosensing devices, clinical applications, such as cardiovascular diseases (CVDs), cancers, diabetes, HIV, and DNA sequence, are also reviewed. In the end, several critical challenges of FET-based biosensing technology are discussed to envision next steps in healthcare technologies.

This paper benchmarks various epitaxial growth schemes based on n-type group-IV materials as viable source/drain candidates for Ge nMOS devices. Si:P grown at low temperature on Ge, gives an active carrier concentration as high as 3.5 × 10 ²⁰ cm ⁻³ and a contact resistivity down to 7.5 × 10 ⁻⁹ Ω.cm ². However, Si:P growth is highly defective due to large lattice mismatch between Si and Ge. Within the material stacks assessed, one option for Ge nMOS source/drain stressors would be to stack Si:P, deposited at contact level, on top of a selectively grown n-Si _y Ge _{1− x− y} Sn _x at source/drain level, in line with the concept of Si passivation of n-Ge surfaces to achieve low contact resistivities as reported in literature (Martens et al. 2011 Appl. Phys. Lett., 98, 013 504). The saturation in active carrier concentration with increasing P (or As)-doping is the major bottleneck in achieving low contact resistivities for as-grown Ge or Si _y Ge _{1− x− y} Sn _x . We focus on understanding various dopant deactivation mechanisms in P-doped Ge and Ge _{1− x} Sn _x alloys. First principles simulation results suggest that P deactivation in Ge and Ge _{1− x} Sn _x can be explained both by P-clustering and donor-vacancy complexes. Positron annihilation spectroscopy analysis, suggests that dopant deactivation in P-doped Ge and Ge _{1− x} Sn _x is primarily due to the formation of P _n -V and Sn _m P _n -V clusters.

In this work, the conduction mechanisms across novel contacts to epitaxial films of pure phase epsilon-Ga ₂O ₃ ( ε-Ga ₂O ₃) were investigated. Different structures made by sputtered metal and oxide thin films were tested as electrical contacts. I-V characteristics show heterogeneous behaviors, revealing different conduction mechanisms according to the applied bias. The results are interesting as they offer a viable method to obtain ohmic contacts on ε-Ga ₂O ₃, which is less studied than other gallium oxide polymorphs but may find application in new electronic and optoelectronic devices. The newly developed ohmic contacts allow to fabricate simple test devices and assess the potential of this material.

The potential of ultrawide-bandgap (UWBG) semiconductors has not been fully explored because of the difficulty of forming a p-n homojunction. In this study, a mixed-dimensional UWBG p-n heterojunction composed of a p-type diamond substrate and an n-type exfoliated β-Ga ₂O ₃ nanolayer has been demonstrated via a van der Waals interaction; this type of structure does not suffer from lattice mismatch. Rectifying current-voltage characteristics with a rectification ratio exceeding 10 ⁷ were obtained with a high reverse hard breakdown voltage of 135 V. This UWBG p-n heterojunction diode exhibited good thermal stability at elevated temperatures, retaining its high rectification ratio and low reverse leakage current. Excellent photoresponse characteristics, including responsivity (12 A W ⁻¹), rejection ratio (8.5 × 10 ³), photo-to-dark-current ratio (3900), and fast response/decay characteristics, were observed from the diamond/ β-Ga ₂O ₃ p-n heterojunction photodiode, showing no persistent photoconductivity. The mixed-dimensional p-n heterojunction diode based on two UWBG semiconductors (p-type diamond and n-type β-Ga ₂O ₃) can be used as a robust building block in next-generation power electronics and solar-blind optoelectronics.

Films of α-Ga ₂O ₃ doped with Sn were grown by halide vapor phase epitaxy (HVPE) on planar and patterned sapphire substrates. For planar substrates, with the same high Sn flow, the total concentration of donors was varying from 10 ¹⁷ cm ⁻³ to high 10 ¹⁸ cm ⁻³. The donor centers were shallow states with activation energies 35–60 meV, centers with levels near E _c–(0.1–0.14) eV (E1), and centers with levels near E _c–(0.35–0.4) eV (E2). Deeper electron traps with levels near E _c−0.6 eV (A), near E _c−0.8 eV (B), E _c−1 eV (C) were detected in capacitance or current transient spectroscopy measurements. Annealing of heavily compensated films in molecular hydrogen flow at 500 °C for 0.5 h strongly increased the concentration of the E1 states and increased the density of the E2 and A traps. For films grown on patterned substrates the growth started by the formation of the orthorhombic α-phase in the valleys of the sapphire pattern that was overgrown by the regions of laterally propagating α-phase. No improvement of the crystalline quality of the layers when using patterned substrates was detected. The electric properties, the deep traps spectra, and the effects of hydrogen treatment were similar to the case of planar samples.

This paper presented a fully depleted silicon on insulator (FD-SOI) MOSFET in nano scale size with deployment the quasi two dimensional β-Ga ₂O ₃ material to improvement electrical properties. The main idea of the proposed structure is embedding a layer of the β-Ga ₂O ₃ in the drain region. Due to the β-Ga ₂O ₃ material features, the electric field distribution near the drain and gate side will be change and peak of the electric field of the proposed structure is diminish. The embedded layer of the β-Ga ₂O ₃ material in our work has an important effects on the electrical and thermal characteristics. In this paper, characteristics of the proposed structure is compared with the prevalent SOI and improvement of characteristics in our work are shown. The features such as the electric field, the potential distribution, the sub-threshold slope, the kink effect, the self-heating effect, punch through effect and DIBL effect are investigated and compared with prevalent SOI.

The developments of high performance InGaN based micro-light-emitting diodes (μLEDs) are discussed. We first review the early demonstrations of μLEDs and the state-of-the-art outstanding achievements on the emerging high-quality display and visible-light communication applications. Due to the miniature dimensions of μLEDs, the key understandings and the significant device advancements to achieve excellent energy efficiency are addressed. Lastly, two other critical challenges of μLEDs, namely full-color scheme and mass transfer technique, and their potential solutions are explored for future investigations.

Bound to complex perovskite systems, ferroelectric random access memory (FRAM) suffers from limited CMOS-compatibility and faces severe scaling issues in today's and future technology nodes. Nevertheless, compared to its current-driven non-volatile memory contenders, the field-driven FRAM excels in terms of low voltage operation and power consumption and therewith has managed to claim embedded as well as stand-alone niche markets. However, in order to overcome this restricted field of application, a material innovation is needed. With the ability to engineer ferroelectricity in HfO ₂, a high-k dielectric well established in memory and logic devices, a new material choice for improved manufacturability and scalability of future 1T and 1T-1C ferroelectric memories has emerged. This paper reviews the recent progress in this emerging field and critically assesses its current and future potential. Suitable memory concepts as well as new applications will be proposed accordingly. Moreover, an empirical description of the ferroelectric stabilization in HfO ₂ will be given, from which additional dopants as well as alternative stabilization mechanism for this phenomenon can be derived.

To improve the blocking performance of Ga ₂O ₃ Schottky barrier diode (SBD), based on the field strength distribution at the bottom of the trench and edge effect, the impacts of structure parameter on breakdown voltage and the figure of merit (FOM) were investigated by TCAD simulation and optimization. The results indicated that the breakdown voltage raised as the corner radius of trench R and the trench length K increased in a certain range, in which K was employed to optimize the structure with a minor mesa width W. In addition, Al ₂O ₃ was confirmed as an appropriate dielectric layer material in Ga ₂O ₃ SBD. When the structure parameters were W = 1 μm, R = 0.6 μm, K = 0.8 μm–0.9 μm and Al ₂O ₃ was selected as dielectric layer materials, a Ga ₂O ₃ trench SBD with breakdown voltage of 3.4 kV and the FOM of over 1.7 GW·cm ⁻² was proposed.

Cobalt (II) phthalocyanine (CoPc) supported on graphene (CVD), carbon black (Vulcan XC72), multi walled carbon nanotube (MWCNT) and their mixtures were evaluated as electrocatalysts for oxygen reduction reaction in acid electrolytes and polymer electrolyte membrane fuel cells (PEMFC). Graphene (G) and carbon supported CoPc catalysts were prepared by impregnation method. Three different temperatures (800 °C, 650 °C and 500 °C) were studied to examine the effect of heat treatment on CoPc and the best fuel cell performance was obtained with samples heat-treated at 800 °C. Maximum power densities of CoPc/G, CoPc/Vulcan-G, CoPc/MWCNT-G, CoPc/MWCNT, CoPc/Vulcan and CoPc/Vulcan-MWCNT at 60 °C cell temperature, 100% humidity and 5 psi back pressure were found as 102, 171, 179, 189, 296, 303 mW cm ⁻², respectively. CVD graphene with CoPc was forming impermeable layer-structure causing mass transport limitations and lower performance. Performance enhancements were achieved by heat-treatment of the samples, higher catalyst loading, operating at high temperatures and higher pressures under 100% humidity. Hybridization of CVD graphene with Vulcan and MWCNT led improved fuel cell performance at 25 psi back pressure compare to individual support materials.

As the feature size of integrated circuits (ICs) shrinks down to 14nm and below, Cobalt (Co) is identified as a suitable barrier layer material. Copper (Cu) has been widely used as the most basic interconnection metallic material for Giant-large scale integrated circuits (GLSI). A higher removal rate (RR) selectivity between Cu and Co is desired to obtain in copper film chemical mechanical polishing (CMP) because the traditional three-step polishing is replaced by two-step polishing of copper and barrier under lower technology nodes. The purpose of copper film polishing is to achieve effective removal of Cu and ultimately stop on the layer of Co. The pH value of slurry is a critical factor affecting the material removal rate and the stability of the slurry. The influence of different kinds of pH regulators and different pH values on the removal rates and the stability of slurries were investigated in this paper. Three pH regulators were chosen in the experiments, containing macromolecular chelating agent FA/OII as organic alkali, KOH as inorganic alkali and KOH mixed with a small amount of tetraethyl ammonium hydroxide (TEAH, C ₈H ₂₁NO) as mixed alkali. According to the investigation of removal rate results and stability experiments results, 10.5 was identified as a suitable pH value and a relatively higher removal rate selectivity was obtained. Meanwhile, using the mixed alkali to adjust slurry pH value can effectively increase the selectivity of Cu and Co and the stability of the copper slurry. The adsorption of TEAH on Cu and Co surface was considered as the critical reason relating to the slight removal rate decline, which was verified by XPS measurements.

The emergence of efficient solid state light emitters was the result of the remarkable breakthroughs in the late 1980s and early 1990s in GaN-based materials and light emitting diodes. Over the past two decades, the continued progress in blue LED efficiency resulted in a revolution in lighting. While the basic physics of nitrides LEDs operation are well understood, nitride LEDs have still open questions, and their reaching physical limits at all wavelengths still raises major challenges.

We investigated the suitability of ammonium persulfate (APS) and potassium oleate (PO) containing silica dispersions for polishing Co interconnects based on removal and dissolution rates, corrosion, post-polish surface quality, and post-polish particle contamination. A slurry consisting of 3 wt% silica, 1 wt% APS and 0.2 mM PO produced a removal rate of ∼465 nm/min at pH 9, along with removal rate selectivity of >100:1 between Co and TiN. The same composition but without abrasives reduced the ΔE _corr between Co and TiN to ∼7 mV and I _gc to ∼0.04 μAcm ⁻², indicating minimal galvanic corrosion. Addition of PO led to no measurable dissolution of the Co films. Surface analysis showed very good post-polish surface quality and minimal contamination with silica particles. These and results obtained with similar H ₂O ₂ containing slurries suggest that the APS and PO-based silica slurry is more suitable for the Co bulk CMP process. The roles of persulfates ions, pH, and PO on the removal process and passivation behavior of Co are discussed and a removal mechanism is proposed.

In this paper we propose a new formula to evaluate in semiconducting Carbon Nanotubes the energy bandgap, i.e. the electronic transition energy from the first valence band to the first conduction band, which is fundamental for electronic applications of CNTs as channel in field effect transistors. The proposed formula is based on empirical correction factors, gained by an optimization procedure aimed at matching experimental data, which results in negligible errors. Moreover the proposed formula shows a new dependence on CNT symmetry indexes (n-m), which has been never observed in literature.

This paper shows how Carbon Nanotubes FETs (CNTFETs) can be used in the design of ternary logic gates, which is a promising alternative to the conventional binary logic design. In particular we propose the design of NOR/NAND gates and of a Decoder, all in ternary logic. The main novelty is that in this paper all simulations are performed in Verilog-A, avoiding so the problems presented in SPICE. At last we show that the proposed ternary logic gates consume significantly lower power and delay time than the previous CNTFET gates implementations.

We have addressed density of states and electrical conductivity of doped graphene like nanotubes for both zigzag and armchair types in the context of tight binding model hamiltonian. The effects of next nearest neighbor hopping amplitude for electrons and gap parameter on electronic density of states and electrical conductivity have been investigated. Green’s function approach has been implemented to find the behavior of electrical conductivity of nanotube within linear response theory. We have found the temperature dependence of electrical conductivity for different values of gap parameter and tube diameter in the presence of neat nearest neighbor hopping integral. The results of electrical conductivity show the increase of diameter leads to increase the conductivity of both zigzag and armchair nanotubes. However the increase of chemical potential reduces the conductivity of armchair nanotube. In the presence of next-to-nearest neighbor hopping amplitude, the density of states results of nanotubes loses its symmetry with respect to energy.

In this paper we present a study of the impact of technology on the CNTFET-based circuits performance. In particular we show the layout of a NOT gate, used as block to build a chain of NOT and a ring oscillator. Then we present the time domain simulations of these circuits in order to see how the parasitic elements could limit the high-speed performances of CNTFETs.

High driving voltage, low power efficiency, and insufficient device stability are the most critical complications for organic light-emitting diodes (OLEDs) on their way to practical applications. Particularly in the case of active-matrix organic light emitting device (AMOLED) displays, inferior electron injection from commonly-used ITO electrodes is a critical issue. In this work, 2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate (MADN:Li ₂CO ₃) is used as an effective electron injecting layer for both inverted and normal bottom-emission organic light-emitting diodes. When the concentration of Li ₂CO ₃-doped MADN is optimized, the device exhibits improved characteristics, including improvements in turn-on voltage, luminance, and efficiency. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses reveal an energy level shift in MADN:Li ₂CO ₃, which indicates the Fermi level of MADN is moving close to its lowest unoccupied molecular orbital (LUMO) and therefore facilitating electron injection from ITO. In addition, the AFM measurement showed the morphology of the Li ₂CO ₃-doped MADN films, revealing good thermal stability in the material related to enhanced lifetime. The results unveiled in this work indicate that Li ₂CO ₃:MADN is a promising electron injecting layer for OLEDs with different device structures and provide a vision of the mechanisms behind this phenomenon.

Due to the continuous increase of multilevel Cu/low- k interconnects, the total thermal budget has been increasing. As a result, the effects of post-annealing on the time-dependent-dielectric-breakdown (TDDB) and electromigration (EM) reliability of Cu/low- k interconnects were investigated in this study. Dense and porous low- k SiCOH dielectric films without or with an SiCNH capping layer were used for comparison. Post-annealing reduced TDDB lifetimes for dense and porous SiCOH dielectric films without a capping layer. With an SiCNH capping layer, annealing at 400 °C had no impact on TDDB lifetime due to the suppression of Cu migration induced breakdown. However, as the annealing temperature increased to 600 °C, both dense and porous SiCOH dielectric films displayed a significant reduction in TDDB lifetimes. The SiCNH capping layer is crucial for EM lifetime improvement due to the reduction of Cu surface migration. With an SiCNH capping layer, the post-annealing influencing EM lifetimes depended on the flow direction of electron. In the case of electron up-flow, EM lifetimes remained unchanged for both dense and porous low- k dielectrics upon annealing at 400 °C. While for electron down-flow case, annealing at 400 °C degraded EM lifetime and the reduction was pronounced for porous dielectric films.

In tungsten (W) film chemical-mechanical-planarization (CMP), the chemical and mechanical reaction behaviors of the W film surface play a critical role in the CMP performance, as determined by oxidation (i.e.,WO ₃), corrosion (i.e., WO ₄ ²⁻), and the electrostatic force at the interface between abrasives and the surface. Unlike a conventional catalyst (i.e., Fe(NO ₃) ₃) for a Fenton reaction in a CMP slurry, a new catalyst ((i.e., potassium ferric oxalate: K ₃Fe(C ₂O ₄) ₃)) and a new nano-scale (i.e., 23 nm in diameter) abrasives (i.e., Zirconia:ZrO ₂) provides specific CMP performance behavior: the maximum W-film polishing rate and a corrosion-free surface are achieved at a specific catalyst concentration (0.03 wt%), and the number of remaining abrasives adsorbed on the W film surface after CMP decreases with increasing concentration of the K ₃Fe(C ₂O ₄) ₃. These CMP performance characteristics are associated with the following results: (i) The degrees of two different CMP mechanisms (oxidation-dominant or corrosion-dominant) determine the corrosion-free surface of W film. (ii) The dependency of the electrostatic force at the interface between abrasives and the film on the K ₃Fe(C ₂O ₄) ₃ concentration determines the polishing rate. Finally, (iii) the zeta potential distribution at the interface between the abrasives and the film directly affects the number of remaining abrasives on the surface after CMP.

Carbon Nanotubes (CNT) are important fillers and reinforcing agents, frequently used in polymeric composites. CNT agglomerate and entangle with each other due to the presence of strong van der Waal forces between them. This agglomeration not only results in decreased product quality but also in lower conductance of composite than expected. Deagglomeration of CNT bundles is necessary for a better dispersion either through chemical functionalization (covalent or non-covalent) or by mechanical methods (stirring, calendering and ultrasonication). This review contains different methods for chemical surface modification of CNT, which not only decrease CNT-matrix interface resistance by providing a soft interface between filler and matrix but also increases CNT dispersion in different types of matrices.

This article provides an overview of the published mechanical stress data for boron- and phosphorus-contained silicate glass films deposited by a variety of chemically vapor deposited (CVD) techniques, i.e. atmospheric and sub-atmospheric pressure (APCVD, SACVD), low pressure, plasma-enhanced (LPCVD, PECVD). The emphasis is done on borophosphosilicate glass films (BPSG) dedicated for the use in micro-electro-mechanical system (MEMS) and micro-opto-electro-mechanical system (MOEMS) technologies as a material with significantly higher film thickness as compared with its traditional use in microelectronics technology as a flow-able planarized interlayer dielectric. The article covers stress features of as-deposited and thermally annealed films with the boron and phosphorus concentration range in between about 1–12 wt%. Phosphorus is detected as a main film component responsible for stress type (tensile or compressive) and its particular values. Film deposition techniques strongly affect the film stress at low phosphorus content in the films, providing either tensile (APCVD, SACVD), or compressive (LPCVD, PECVD) stress types. These effects explained with differences in CVD kinetics and hydrogen-contained CVD reaction by-products formation.

Due to the broad application prospects of optoelectronic devices and microwave devices at high temperature and power, the process of Metal Organic Chemical Vapor Deposition (MOCVD) of AlGaN of the key material AlGaN has been extensively researched in the past 30 years. In order to enhance the quality of AlGaN layers, researchers continuously analyzed their growth mechanism and optimized the growth process through experimental and theoretical studies. In this work, based on reviewing previous studies, we summarize the research progress for AlGaN grown by MOCVD and discuss the existing problems and future research priorities.

The Mn ⁴⁺ and Cr ³⁺-activated phosphor properties are examined in detail from an aspect of spectroscopic point of view. The phosphor materials discussed here are fluorides and oxides. Such Mn ⁴⁺ and Cr ³⁺-activated fluoride and oxide phosphors are classified from a different kind of host materials together with the different spectroscopic properties of photoluminescence (PL) and PL excitation (PLE) spectra into five groups: types F-Mn (F = fluoride), F-Cr, O-Mn (O = oxide), O-Cr-A, and O-Cr-B. The spectroscopic properties of the Mn ⁴⁺ and Cr ³⁺-activated phosphors are examined by analyzing PL and PLE spectra based on the Franck−Condon analysis model. The results show that an energy inequality relation of the zero-phonon line (ZPL) energies for types F-Mn, O-Mn, and O-Cr-A phosphors is given by E( ² E _g ) _ZPL < E( ⁴ T _{2 g} ) _ZPL, whereas that for types F-Cr and O-Cr-B phosphors is given by E( ² E _g ) _ZPL ≥ E( ⁴ T _{2 g} ) _ZPL. As a result, the former phosphors promise to emit light caused by the ² E _g → ⁴ A _{2 g} transitions and the latter ones by the ⁴ T _{2 g} → ⁴ A _{2 g} transitions. Difference in the temperature-dependent PL intensity between the Mn ⁴⁺ and Cr ³⁺ red and deep red emissions are also discussed in detail.

Seeking more economical alternative electrocatalysts without sacrificing much in performance to replace precious metal Pt is one of the major research topics in hydrogen evolution reactions (HER). Tungsten disulfide (WS ₂) has been recognized as a promising substitute for Pt owing to its high efficiency and low-cost. Since most existing works adopt solution-synthesized WS ₂ crystallites for HER, direct growth of WS ₂ layered materials on conducting substrates should offer new opportunities. The growth of WS ₂ by the thermolysis of ammonium tetrathiotungstate (NH ₄) ₂WS ₄ was examined under various gaseous environments. Structural analysis and electrochemical studies show that the H ₂S environment leads to the WS ₂ catalysts with superior HER performance with an extremely low overpotential (η ₁₀ = 184 mV).

Rb-based hexafluoride red-emitting phosphors, Rb ₂SiF ₆:Mn ⁴⁺ and Rb ₂TiF ₆:Mn ⁴⁺, were synthesized by the coprecipitation method. Optical microscopy observation, X-ray diffraction (XRD) measurement, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and luminescence decay characteristics measurements were used to study the structural and optical properties of the phosphors. The photographs of the bulk samples showed clear crystallographic habits originating from the cubic and trigonal symmetries of the Rb ₂SiF ₆ and Rb ₂TiF ₆ hosts, respectively, in agreement with the XRD results. The phosphors exhibited an intense narrow-band Mn ⁴⁺ ( ² E _g → ⁴ A _{2 g} ) red emission with internal quantum efficiencies higher than 90% upon blue light excitation. The Franck−Condon analysis of the PLE data yielded the Mn ⁴⁺ intra- d-shell transitions to occur at ∼2.47 eV (∼2.34 eV) for the ⁴ A _{2 g} → ⁴ T _{2 g} transition and at ∼2.86 eV (∼2.83 eV) for the ⁴ A _{2 g} → ⁴ T _{1 g} transition in the Rb ₂SiF ₆:Mn ⁴⁺ (Rb ₂TiF ₆:Mn ⁴⁺) phosphor. Temperature dependence of the PL spectra from T = 20 to 500 K gave the quenching temperature values ( T _q’s) at which the PL intensity has fallen to half its maximum value to be T _q ∼ 490 and ∼450 K for Rb ₂SiF ₆:Mn ⁴⁺ and Rb ₂TiF ₆:Mn ⁴⁺, respectively, promising for use as high-temperature stable phosphors in solid-state lighting applications.

Optical and photoacoustic properties of Ce ³⁺-doped lanthanide (Lu, Y, Gd) aluminum garnet were investigated. In the photoacoustic (PA) spectra, the 5 d ₁ (lowest 5 d level) band of Ce ³⁺ was observed at around 450 nm in the obtained Ce ³⁺-doped garnet samples. This result shows that a part of the excited energy is converted to thermal energy, which is generated by some nonradiative processes. In Y ₃Al ₅O ₁₂:Ce ³⁺, the 5 d ₁ PA peak wavelength is shorter than the 5 d ₁ photoluminescence excitation peak wavelength, which indicates that part of the heat generation is caused by the phonon relaxation process within 5 d ₁ state. The PA intensity and luminescence quantum efficiency of the Ce ³⁺-doped gadolinium yttrium aluminum garnets ((Gd _0.5Y _0.5) ₃Al ₅O ₁₂, (Gd _0.75Y _0.25) ₃Al ₅O ₁₂) are much stronger and smaller, respectively, than those of Y ₃Al ₅O ₁₂:Ce ³⁺. Based on these results and the persistent luminescence excitation spectra, we conclude that (Gd _0.5Y _0.5) ₃Al ₅O ₁₂:Ce ³⁺ and (Gd _0.75Y _0.25) ₃Al ₅O ₁₂:Ce ³⁺ possess the additional heat generation process explained by the thermal ionization.

The radiation tolerance of AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on high quality, low threading dislocation density (TDD) ammonothermal GaN and hydride vapor phase epitaxy GaN substrates was studied and compared to the radiation response of devices on SiC substrates where the TDD is 10 ⁴ times higher. Hall and transport measurements were performed as a function of 2 MeV proton fluence. The threading dislocation density had no effect on the radiation response. Comparing the results with published data reveals that almost all irradiated GaN-based HEMTs respond to radiation damage similarly regardless of differences in initial film quality, device structure, aluminum mole fraction, etc. AlGaAs/GaAs HEMTs are also shown to behave similarly but are around ten times more sensitive to radiation damage than GaN-based HEMTs. Known values of the displacement energy thresholds in GaN and GaAs are used to calculate that 36% fewer defects are created in GaN than in GaAs, which is too small to cause a 1000% difference in radiation sensitivity between GaN- and GaAs-based HEMTs. An alternative explanation is proposed in which the piezoelectric field at the AlGaN/GaN interface causes scattered carriers to be reinjected into the 2DEG channel, thereby mitigating some of the harmful radiation effects.

This paper proposes using hourglass-shaped metal filaments to improve the ON/OFF resistance ratio and retention characteristics of switching devices used in reconfigurable logic applications. These filaments are obtained by controlling the Cu-ion mobility in multi-layer oxide electrolytes. By adopting an upper AlO _X and lower TiO ₂ electrolyte layers with respectively low and high Cu-ion mobility, we could form hourglass-shaped filaments as a result of suppressed Cu-ion injection and enhanced filament lateral growth. The hourglass-shaped metal filaments induced local Joule heating at the filament constriction, thus accelerating RESET operations. We confirmed that, as a result, Cu/AlO _X/TiO ₂/W devices show high ON/OFF resistance ratios (>10 ⁶) and ∼10-year retention properties at 80°C.