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Selective laser melting (SLM) was used for additive manufacturing multi-wall carbon nanotube (MWCNT) reinforced Inconel 625 composites. The MWCNTs were coated on Inconel 625 powder through molecular-level mixing. Compared to the SLM fabricated Inconel 625 sample, the composite sample showed significant improvement in ultimate tensile and yield strength with less elongation. Heat-treatment on the composite sample recovered its elongation to the level of pure Inconel 625 while maintaining its ultimate tensile strength but reducing its yield strength. The microstructures of the composite sample had a slightly faster cooling rate than the pure metallic sample during SLM fabrication. The electron backscatter diffraction graphs revealed the grain refinement induced by MWCNTS in the alloy matrix. The Raman spectra and TEM micrographs revealed the presence of MWCNT in the metal matrix after SLM fabrication. Keywords: Selective laser melting, Inconel 625, Carbon nanotube, Metal matrix composite, Heat treatment

Earth abundant materials based photoelectrochemical cells (PECs) are designed using aluminium alloyed iron silicide (FeSi(Al)) as auxiliary electrode, tungsten oxide (WO3) and iron-oxide (Fe2O3) as working electrodes for solar driven hydrogen (SH) production. Low temperature grown metallic α-phase and semiconducting β-phase FeSi(Al) are introduced as auxiliary electrode and hydrogen evolution performance is compared with commercially available platinum electrode. The β-phase FeSi(Al) electrode yields similar hydrogen evolution compared with platinum electrode and are highly stable in electrolyte solution. This study shows that the earth-abundant iron-silicide and cheap metal oxides based PEC cells provide great potential toward Pt-free devices for the development of sustainable and low cost PECs for large scale solar hydrogen production.

In this work, Ga-doped Geranium (Ge) films have been grown on GaAs (100) substrates by metal-organic chemical vapor deposition (MOCVD). Undesired pillar structures have been observed on the epilayers prepared at relatively lower temperatures. Energy dispersive X-ray spectroscopy (EDX) indicated that the pillars are mainly consisted of Ga atoms, which is totally different from that of the Ge film. It was demonstrated that the pillar structures could be reduced by simply raising the growth temperature while keeping the other growth conditions unchanged. In this regard, the growth mechanism of the pillars was related to the Ge-Ga dimers formed during the growth of p-Ge films. By further studying the influence of a GaAs or Ge buffer layer on the growth of p-Ge layers, we found that the GaAs substrate with lower density of Ga or Ge dangling bonds was helpful in suppressing the formation of the undesired pillar structures.

Solar radiation and hydrogen generation via splitting water molecules have been recognized as sustainable and clean energy sources having great industrial potentials. In this regard, thin film materials for photovoltaic and photoanodes applications have been widely developed in the last decade. For thin film photovoltaic applications, taking material availability, extraction/processing cost, energy conversion efficiency, and eco-friendliness into account, FeS 2 (pyrite) has been predicted to hold the leading position among the most plausible candidates such as Cu 2 S, Cu 2 O, CuO, etc. On the other hand, feasible water splitting on nanostructured surface and/or hybrid nanostructures has been observed in the last few years. In terms of processing cost, feasibility in scale-up for mass production, material engineering for efficiency, etc., physical vapor depositions (PVDs), e.g., magnetron-sputtering deposition, have great advantages. Here, we present our recent studies on synthesis of iron sulfide and oxide layered and nanostructured films by combining PVD and thermal vapor sulfurization/oxidation techniques.

Structural properties and solar cells performance of sputter grown sub-micrometer thick (~600 nm) Cu 2 ZnSnS 4 (CZTS) films are investigated for low cost and large scale photovoltaic deployment. The CZTS films are deposited using single quaternary stoichiometric target at room temperature. X-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy measurements were carried out to investigate the structural property and secondary phase formation. The intense phonon peak at 334 cm −1 in the visible Raman spectra confirms the deposition of single phase CZTS films. CZTS-based thin film solar cells show excellent performance with open circuit voltage ~600 mV and over all cell efficiency of ~3.07%, exhibiting commercial potential toward large scale fabrication of photovoltaic devices.

We have synthesized crystalline MoS2 thin films on Si substrates by thermal processing of molybdenum layers in sulfur vapor environment at elevated temperatures. The molybdenum layers were deposited at room temperature by magnetron sputtering. X-ray diffraction, Raman scattering spectroscopy, and transmission-electron microscopy characterizations revealed that the synthesized MoS2 thin films are of hexagonal crystal with van der Waals layered structures that bended into bell-like domains. Amorphous SiO2 layers have been observed not only at the MoS2/Si interface but also anomalously on top of the MoS2 layer. Secondary ion mass spectroscopy has been employed to investigate the elemental depth profiles, which, together with the structural properties, provides evidence that the surface SiO2 was grown out from its bottom layers rather than deposited from the growth environments. A mechanism based on solid-state reactions and atomic diffusions is introduced to explain the formation of the observed SiO2/MoS2/SiO2 sandwich structures, which may have important consequences when fabricating and/or processing MoS2/Si heterostructures for electrical and optoelectronic applications.

Single atom catalysts (SACs) have recently been intensively explored for electrochemical nitrogen reduction reaction (NRR) because of the 100% utilization, high activity and high selectivity, in which N-doped substrates are widely used to support the SACs. Herein, we show that monolayer molybdenum disulfide (MoS2) is a potential alternative substrate to anchor transition metal (TM) SACs towards NRR. Through the first-principles high-throughput screening, we find that the single molybdenum atom (Mo) anchored on top of the Mo site of MoS2 (Mo@MoS2-M) has the best NRR performance among Ag, Au, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pd, Pt, Rh, Ru, Sc, Ti, V, W and Zn. The estimated overpotential of Mo@MoS2-M is around 0.28 V via the distal mechanism. Our results further confirm the stability of the Mo@MoS2-M as well as its good selectivity to NRR against hydrogen evolution reaction. These results pave a way to explore the new single atom-substrate pair towards high-performance nitrogen reduction.

The authors report on high quality TiO2 epilayers grown on lattice-matched LaAlO3 substrates by pulsed laser deposition. A prototype of metal–semiconductor–metal ultraviolet (UV) photodetector based on TiO2 was fabricated by employing Au as the Schottky contact metal. The UV–visible transmittance spectrum of the TiO2 epilayer and the spectral response of the photodetector reveal that the deposited anatase TiO2 thin film exhibits excellent visible-blind UV characteristics with an optical bandgap of 3.25 eV. In addition, the fabricated photodetector exhibits a high UV-to-visible rejection ratio (R270 nm/R400 nm) of 105 while displaying a low dark current of 0.25 pA under 5 V bias and a high responsivity of 0.21 A/W, suggesting a potential application in UV photodetection.

Growth of alpha phase aluminum alloyed iron silicide (α-phase FeSi(Al)) ternary alloy on silicon (Si) substrate at a temperature of 600 °C has been reported. The α-phase FeSi(Al) thin films are grown on Si substrate by using conventional sputter deposition and rapid thermal annealing (RTA) treatment. The transition temperature of α-phase FeSi2 reduces to 600 °C through incorporating aluminum into the silicide films. Thickness of amorphous silicide layer and aluminum composition are very critical to grow highly texture α-FeSi(Al) layer at a lower temperature. The α-FeSi(Al) film shows a preferential orientation (001) after annealed at temperature of 600 °C through the formation of thin film epitaxial silicon at the interface. The α-FeSi(Al) films tends to show a polycrystalline nature with the increase on annealing temperature to 700 °C. The α-FeSi(Al) ternary alloy has high work function of ∼5.3 eV. The low temperature grown α-phase FeSi(Al) can be applied for renewable energy and electronic applications as an electrode.

Development of high quality p-type epitaxial gallium–arsenide (epi-GaAs) on germanium (Ge) with sub-nm surface roughness is much sought after for the next generation high speed transistors application. High quality zinc doped p-type epitaxial GaAs with surface roughness of ~0.87 nm was grown on Ge substrates at 675 °C. Thin Al0.3Ga0.7As buffer layer and un-doped GaAs of 300 nm thick were introduced to suppress the Ge defects and auto-doping into epi-GaAs layer. The material and optical properties of the p-type epi-GaAs/un-doped GaAs/Al0.3Ga0.7As/Ge structures were examined through PL and Raman analysis. The metal–oxide–semiconductor capacitor (MOSC) was fabricated using p-type epi-GaAs layer and atomic-layer-deposited Al2O3 gate dielectric. The effective dielectric constant of the Au/Al2O3/p-epi-GaAs gate-stack is 5.9 and hysteresis voltage of 500 mV was observed. The epi-GaAs layer is p-type in nature with doping densities of 5×1017 cm−3.

We report on the effect of strain relaxations induced by lift-off in an InGaN/GaN multiple quantum wells (MQWs) blue light-emitting diode (LED) structure grown by metal-organic chemical vapor deposition (MOCVD) on a 150-mm diameter Si (111) substrate. To manage the lattice strain and, meanwhile, filter the threading dislocations, an AlN nucleation layer followed by a fourfold-step-graded AlGaN buffer together with multiple low-temperature AlN interlayers hasbeen employed, which results in a crack-free growth of 4.9-µm GaN on Si (111) in the studied LED structure. High-resolution x-ray diffraction (HRXRD) and micro-Raman spectroscopy reveal that MQWs are coherently grown on the GaN layer while the GaN layer is tensile strained on the Si (111) substrate. Lift-off by wet-chemical etching results in phonon softening of both the top-layer GaN and the InGaN within the QWs; meanwhile, a red-shift of ~11 meV in the photoluminescence (PL) from the MQWs accompanied by a significant decrease (>4.9 times) in the PL-peak decay time is observed at room temperature. These observations are discussed and associated with the lift-off induced strain relaxations, which change the wafer curvature that in turn results in redistribution of in-plane stresses along the growth direction in the GaN-on-Si LED structure.

We report on unintentional carbon depositions induced by electron-beam irradiation on the surface of high-indium-content AlInN thin films in a scanning-electron microscope (SEM) chamber. With a beam voltage of 10 kV and a probe current of 160 µA, a nano-scale dot evolves during a 5-min irradiation. By increasing the irradiation time, the dot grows in diameter and height. The dot size when compared with that grown on a Si substrate under the same conditions is much smaller. Energy-dispersive X-ray spectroscopy reveals a linear increase in carbon deposition as a function of irradiation time and the rate of increase is larger on AlInN than that on Si. These observations, together with the remarkable morphology evolutions around the dot on AlInN rather than on Si, provide evidence that the surface mobility of the adsorbed molecules is larger on Si than that on AlInN. The reduced surface mobility on AlInN is attributed to surface roughness, the existence of an electron accumulation layer, and columnar grain structures of the AlInN layer. These properties can be used to benefit the fabrication of small structures on the AlInN surface without affecting the surroundings.

Post-growth thermal oxidations of InN have been studied using high-resolution x-ray diffraction (HRXRD) and secondary ion-mass spectroscopy (SIMS). The InN thin films, having relative high crystal quality, were grown by metal–organic chemical vapor deposition (MOCVD) on c-sapphire substrates using InGaN/GaN buffer layers. HRXRD reveals that oxidation of wurtzite InN into body-center cubic In2O3 occurred at elevated temperatures. A Si3N4 encapsulation improves the crystal quality of In2O3 oxidized by using conventional rapid thermal annealing (RTA) but it results in the presence of undesired metallic indium. Cycle-RTA not only improves the crystal quality but also avoids the byproduct of metallic indium. SIMS depth profile, using contaminate elements as the ‘interface markers,’ provide evidence that the oxidation of InN is dominated by oxygen inward diffusion mechanism. Together with the HRXRD results, we conclude that the crystal quality of the resultant In2O3/InN heterostructure is mainly controlled by the balance between the speeds of oxygen diffusion and InN thermal dissociation, which can be effectively tuned by cycle-RTA. The obtained In2O3/InN heterostructures can be fundamental materials for studying high speed chemical/gas sensing devices.

Yb-doped WO 3 photocatalysts were prepared by co-sputtering WO 3 and Yb, followed by annealing in air for water oxidation with visible light. All the obtained photocatalysts were monoclinic with sputtering power of Yb up to 10 W and displayed no optical absorption red shift. In photoelectrochemical (PEC) studies, the photocurrent densities were improved with up to 0.34 at.% Yb in WO 3, with the highest photocurrent of 1.3 mA/cm 2 (1.2 V vs. Ag/AgCl) achieved with 3 photocatalyst. The improvement in photocurrent density was attributed to enhanced conductive carrier path, increased oxygen vacancies and 4f 13 orbital configuration due to Yb 3+ substitution of W 6+ .

Thin film WO 3 photoanodes were prepared by reactive sputtering in Ar and O 2 gas mixtures of various flow rate combinations. Furnace annealed films were nanocrystalline monoclinic WO 3 with (002), (020) and (200) plane orientations. Water oxidation in 0.33 M H 2 SO 4 electrolyte under simulated solar illumination showed that photoanodes deposited in highest Ar and O 2 flow rate combinations exhibited highest photocurrent of 4.1 mA cm −2 (at 1.3 V vs Ag/AgCl) compared to 3–3.8 mA cm −2 for photoanodes deposited in lower flow rate combinations. The higher photocurrents were ascribed to lower bulk resistivity and charge transfer resistance at the WO 3 /electrolyte interface. These photoanodes consisted of randomly oriented (002), (020) and (200) planes in contrast to the preferentially orientated (002) and (200) planes of photoanodes which were highly resistive with poorer photocurrent responses. These results were interpreted in terms of the effects of Ar:O 2 flow rate combinations on the distribution of oxygen vacancies and formation of crystallographic shear planes in the sputtered films.

This critical review surveys β-FeSi2 research over the years with focus on reviewing recent development in β-FeSi2-based light emitting diodes (LEDs). Based on theoretical analyses and comparison to experimental results reported in the literature, weak carrier confinement in the β-FeSi2 active layer has been identified as the likely cause for poor room-temperature electroluminescence (EL) performance of p-Si/p-β-FeSi2/n+-Si double hetero-junction LEDs. Solutions to overcome this limit have been proposed together with new research directions.

Ultra thin HfO2 high-k gate dielectric has been deposited directly on strained Si0.81Ge0.19 by atomic layer deposition process. Important electrical properties such as, interface trap density, charge trapping behavior, and low-frequency noise characteristics have been studied in detail. Grazing incidence X-ray diffraction analysis shows that the conversion from amorphous to crystalline phase start to appear in the HfO2 films when annealed between 400 and 500 °C. Interface trap density was found to be in the range of 4.0–5.6 × 1011 eV− 1 cm− 2. Results of internal photoemission studies on pre-existing charge trapping for different processing conditions; without annealing and annealed in O2, N2 and mixed (O2 and N2) ambient are presented. Low-frequency noise characteristics of HfO2/Si0.81Ge0.19 stacks annealed in different gas ambient have been measured using metal–insulator–semiconductor capacitors (contact area ~ 2 × 10− 3 cm2). It is found that the sample annealed in N2 gas ambient shows better electrical properties in general compared to samples annealed in O2 and/or mixed (O2 and N2) gas ambient.

High quality Ge epitaxy on a GaAs (100) substrate was grown by metal-organic chemical vapor deposition using germane. The effects of growth temperature and deposition rate on the quality of the Ge epitaxy are investigated. Significant improvement in surface root-mean-square roughness is observed with increasing Ge growth temperature or deposition rate, while keeping all other deposition parameters unchanged. Investigation of the Ge material quality grown after different GaAs surface preparation conditions shows that Ga rich surfaces are beneficial for smooth Ge surfaces, which is attributed to the formation of Ge–Ga bonds at the initiation of the Ge deposition. The good crystalline quality of grown Ge film was further confirmed by high-resolution X-ray diffraction and secondary ion mass spectrometry characterization.

High-quality, dopants controlled and heterostructure engineered GaN-based nanobelts are highly desirable for fabricating nanogenerators and piezotronic devices with high-output and stable performance, but such structures cannot be easily fabricated using the well established techniques such as the vapor-phase deposition method. We describe a new approach for fabricating high-quality GaN-based nanobelts via strain-controlled cracking of thin solid films. By epitaxially growing InGaN/GaN bilayer film along its [112¯0] crystal axis on an r-plane sapphire substrate with ZnO serving as a sacrificial buffer template, the in-plane elastic stress can be asymmetrically stored in the bilayer film with the component along [11¯00] axis much larger than that along [0001] axis. A lateral wet-chemical etching of the ZnO template causes the InGaN/GaN bilayer film to peel off with a rational cracking in parallel to [112¯0] while perpendicular to [11¯00] and [0001]. The cracking-fronts proceed along the [0001] axis with the increase in etching time, forming parallel allied nanobelt arrays. Such structures can be the fundamental materials for studying piezotronic and piezo-phototronic devices.

Thin film solar cells of β -FeSi2(Al)/Si heterojunctions were fabricated via Al incorporation and rapid thermal processing (RTP). The Al-incorporated FeSi2 films were polycrystalline, orthorhombic and semi-conducting. Photo-voltaic characterisation showed that device prepared with Al interlayer added between Al-doped FeSi2 film and Si exhibited short-circuit current and open-circuit voltage improvement over device without interlayer. These can be correlated to surface passivation of Si by interfacial structure and reduced dark current with Al interlayer. This alternative fabrication method via Al incorporation to β -FeSi2 films using conventional magnetron sputtering and RTP enhances the viability of β -FeSi2 for photovoltaic application.

Ultra thin HfAlO"x high-k gate dielectric has been deposited directly on Si"1"-"xGe"x by RF sputter deposition. The interfacial chemical structure and energy-band discontinuities were studied by using X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (TOF-SIMS) and electrical measurements. It is found that the sputtered deposited HfAlO"x gate dielectric on SiGe exhibits excellent electrical properties with low interface state density, hysteresis voltage, and frequency dispersion. The effective valence and conduction band offsets between HfAlO"x (E"g=6.2eV) and Si"1"-"xGe"x (E"g=1.04eV) were found to be 3.11eV and 2.05eV, respectively. In addition, the charge trapping properties of HfAlO"x/SiGe gate stacks were characterized by constant voltage stressing (CVS).

Wedge indentation experiments are performed to study the time-dependent fracture behavior of silica-based low-k films, namely BlackDiamond® (BD) film and methysilsesquoxane (MSQ) film, both on Si substrate. Two wedge indentation tests, load-holding and varying-loading-rates tests, are performed in this study. It is found that the chemical structure of the low-k films greatly influences the crack growth during the load-holding and varying-loading-rates tests. For the MSQ/Si system, continuously increasing indentation load to above the critical load (>2 mN) is required for crack growth; while for the BD/Si system, spending excessive period of time at below the critical load (

This paper presents further studies to determine the interface toughness of low- k films (black diamond (BD) film) using wedge indentation experiments and analysis. In addition, the effects of film thickness on the delamination mode are studied and an analysis methodology is proposed. The curvature of the delamination crack front is measured and compared for the films with different thicknesses, and this information is used to determine the critical buckling stress and the delamination mode: i.e. with or without buckling. For a thinner film with a straight crack front, there is greater likelihood of buckling delamination, while for a thicker film with a curved crack front buckling is less likely. Combining these results with those from a previous study, it is shown that the wedge indentation test is capable of accurately measuring the interface toughness of low- k films, and a pop-in event in the load–penetration curve can be used as an early indication of interface crack initiation. It is also found that the resistances to the initiation and propagation of the interfacial cracks for the porous methylsilsesquioxane (MSQ) and non-porous BD films are significantly different; this could be due to the fact that in the porous MSQ film, molecular bridges might provide an additional mechanism to resist interfacial delamination cracks.

As the industry approaches sub-100 nm technology nodes, the trend is to replace cobalt silicide with nickel monosilicide (NiSi) since the use of NiSi for contact metallization shows a number of technological advantages, including its line-width independent low resistivity, less Si consumption and low thermal budget for its formation, and compatibility with Si1 − xGex substrate technology. However, NiSi has not been considered as a serious candidate until recently mainly due to its poor morphological/thermal stability. Recent studies have shown that the morphological/thermal stability of NiSi can be enhanced substantially through the addition of a small amount of impurities, resulting in much improved silicided shallow junction integrity. Moreover, it has also been demonstrated that the addition of certain impurities, such as Ti, effectively reduces the sensitivity of NiSi formation to surface contaminants (e.g., residual interfacial oxide). This paper will present and discuss the details of these experimental results.

Deep level transient spectroscopy has been used to characterize the deep levels in InGaN/GaN grown on sapphire substrate as well as on free-standing GaN. The deep levels at Ec − Et ∼ 0.17–0.23 eV and Ec − Et ∼ 0.58–0.62 eV have been detected in our samples which are present in GaN samples reported by others. These two deep levels have been attributed by us to threading dislocations as they exhibit logarithmic capture kinetic behavior and are found to be substantially reduced in its trap concentration (∼ from 1014 to 1012 cm− 2) in GaN grown on free-standing GaN template. Other than the two deep levels, an additional level at Ec − Et ∼ 0.40–0.42 eV has been identified in both samples, which is believed to be related to In segregation. AFM image shows region of pits formation in InGaN epilayer for sample grown on u-GaN using sapphire substrate while the latter gives a much smoother morphology. From the X-ray diffraction space mapping, the mosaicity of the sample structure for both samples were studied. Dislocations do not play a significant role in the structural properties of InGaN grown on free-standing GaN since the FWHM based on the Δ ω is relatively small (± 0.15°) in the case of InGaN/GaN on free-standing GaN substrate as compared to that on sapphire (± 0.35°). The wider spread in Δω–2θ value for InGaN layer on free-standing GaN also suggested the effect of compositional pulling with increasing InGaN layer thickness.

In a materials study of ErSi 2 /Si(001) as a potential candidate for Schottky source/drain NMOS application, the properties of ErSi 2 thin film were investigated with varying degrees of Si(001) surface amorphization. The amorphization was carried out by in situ Ar plasma cleaning and Si pre-amorphization implant. It was found that the ErSi 2 thin film becomes smoother but less textured and less epitaxial with Si(001) with increasing degree of the Si surface amorphization. In addition, an increased oxygen penetration during rapid thermal annealing occurs with increasing substrate amorphization.

Solid-state reactions between Er and Ge (001) under different processing conditions were investigated. Under normal rapid thermal processing (RTP) in high-purity N2 ambience, the Er–Ge film formation was Fcontaminated_ with Er2O3 even at low temperature annealing. Ti capping of Er films before RTP delayed Er2O3 formation with the Ti cap acting as a sacrificial layer for the Er underneath. Vacuum annealing of Er films significantly reduced Er2O3 formation even after higher temperature annealing. High quality Er–Ge films can thus be formed through solid-state reaction of Er and Ge if oxygen contamination from annealing ambient during RTP is controlled. The Er–Ge phase had low sheet resistance values averaging 3 to 4 V/sq. ErGe1.8 was formed from the solid-state reaction between Er and Ge(001) in vacuum. D 2005 Elsevier B.V. All rights reserved.

A process to stabilise the formation of NiGe using Zr alloying engineering approach was investigated. The NiGe film maintained continuity up to 600 °C with NiGe phase stable up to 700 °C. Secondary ion mass spectroscopy and transmission electron microscopy characterisations showed that a thin ZrO x layer was formed on top of NiGe. The ZrO x layer acted as a capping layer to NiGe. As a result, the morphology and phase formation of NiGe were stabilised. We propose Ni(Zr) alloy as a promising material for germanides metallisation contacts in metal-oxide-semiconductor field-effect transistors (MOSFETs).

In this study, we survey Schottky diode property of both p-metal (Ni) germanide and n-metal (Zr, Er and Yb) germanide in contact with Ge (100). Our experimental results demonstrate that Φp values obtained for NiGe/n-Ge is − 0.07 eV, and Φn values for YbGe/p-Ge is 0.139 eV, the lowest hole barrier so far reported. In addition, NiGe Schottky source/drain p-MOSFET with HfO2/TaN gate stack and AlN/SiO2 stacked spacer were fabricated and measured. The drain current at VD = VG − Vth = − 1.5 V is ∼ 4.0 μA/μm of the gate length LG = 8 μm device. The Ion/Ioff ratio is ∼ 103, and sub-threshold swing is 137 mV/dec.

Low-k material is susceptible to the plasma damage in fabrication of damascene structure and hence the metal barrier performance will be affected. It is very important to characterize the effect of plasma process on metal barrier performance and fundamentally understand interfacial interaction between low-k material and metal barrier layer for implementing low-k, especially ultra low-k in Cu interconnect on 65 nm node and beyond. In this paper, we present our studies on the effects of two key plasma processes, H2/He reactive plasma clean treatment (RPC) and H2/N2 etch, on the barrier layer performance. We also present a solution to enhance the Ta barrier layer performance. The new implementation successfully prevented Cu from diffusing into polymer low-k after annealing at 200 °C for 1000 h. The methodology is proven to be effective for characterizing and improving pore-sealing and barrier performance for Cu/porous ultra low-k interconnect.

Bulk alloy annealing experiments indicate that a NiSi + Si ↔ NiSi 2 eutectoid reaction exists in the Ni–Si binary system between 705 and 735 °C. The eutectoid temperature is consistent with temperatures often observed for the nickel monosilicide-to-disilicide transformation in nickel silicide thin films on crystalline silicon substrates.

The reaction of Ni with Ge, Si 0.75 Ge 0.25 and Si using rapid thermal annealing (RTA) and in-situ annealing method at 400°C produces different phases, as revealed by cross-sectional transmission electron microscopy (TEM). A uniform film of nickel germanide (NiGe) was formed at 400°C for the Ni reaction with Ge using the in-situ annealing technique, whereas Ni 3 Ge 2 and NiGe phases were found using the RTA method. For the reaction between Ni and Si, a highly textured NiSi film was obtained at 400°C for RTA whereas Ni 3 Si 2 and NiSi were found using the in-situ annealing method. On the other hand, a relatively uniform NiSiGe was formed using RTA; Ni 3 (Si 1-y Ge y ) 2 and Ni(Si 1-x Ge x ) (x

The AlInGaN alloy has emerged as the material for potential use in UV light emitting diodes and lasers due to its higher emission quantum efficiency. However, surface defects like hexagonal pits appear on the surface of this quaternary alloy and formation of these pits can degrade the device performance. In this study, we have observed inverted hexagonal pits formation in AlInGaN epilayers grown on sapphire. The pits depth and diameter are found to increase with the epilayer thickness and pits agglomeration occurs when epilayer thickness is higher than 40 nm. Cross-sectional atomic force microscopy images of the inverted hexagonal pits show that these pits are truncated. This is probably due to the filling of pits associated with composition pulling effect in AlInGaN epilayers. An enhanced yellow luminescence emission is also detected from these inverted hexagonal pits. This is probably due to impurity decoration along the threading dislocations, which are terminated at the vertex of the pits. These impurities form deep levels and serve as effective transition levels for yellow luminescence emission.

Small ZnO structures including nano- and submicron-crystals have been deposited on Si and GaAs substrates by employing thermal-evaporation method. It is revealed that under the chosen growth conditions a decrease in growth temperature by locating the Si substrate away from the source crucible tends to enrich ZnO crystals with zinc element, which is in turn beneficial to the growth of nanoneedles on Si substrates. In the growth without zinc enrichment, hierarchical networks of ZnO submicron wires are observed on GaAs substrates instead of ZnO nanoflakes on Si substrates while an introduction of a low-temperature (LT) ZnO template on GaAs substrates results in a film of ZnO crystallites. Photoluminescence (PL) collected at room temperature from the ZnO crystallites film exhibits a strong near-bandedge emission at 3.275 eV, which is enhanced, narrowed, and blue shifted by employing the LT-ZnO template. These changes are attributable to a suppression of As doping in ZnO caused by atoms evaporation and/or diffusion from the GaAs substrate.

Differential Scanning Calorimetry (DSC) was used to study the effect of Al incorporation on the crystallization of β-FeSi 2 film on SiO 2 /Si(100) substrate. An exothermic reaction pertaining to the crystallization of β-FeSi 2 , confirmed using X-Ray Diffraction, can be observed by heating a 1.2 μm amorphous FeSi 2 film in the DSC. Using Kissinger analysis, the activation energy of thin β-FeSi 2 crystallization was determined to be 2.63 ± 0.05 eV. In this study, it was found that the activation energy for β-FeSi 2 crystallization increases with Al incorporation by co-sputtering. Hall measurements show the Al incorporated β-FeSi 2 to be P-type.

Deep levels in InGaAlP films grown using two different V/III ratios have been studied by employing deep level transient spectroscopy (DLTS). The two samples investigated have the same composition of (Al0.3Ga0.7)0.51In0.49P and a film thickness of 0.6 μm, but grown with V/III ratios 75 and 50. Two defect levels with activation energies 0.23 and 0.78 eV are detected by temperature-scan DLTS in the sample with a V/III ratio of 75, with the 0.78 eV level being the dominant peak. Their respective capture cross-sections are 1.2×10−16 and 3.8×10−13 cm−2. The 0.78 eV trap level is also analysed using isothermal DLTS measurement and similar values of thermal signatures are obtained. The DLTS spectrum of the 0.78 eV trap level has been found to be broader than that expected for a point-type defect, implying that it may be associated with a complex or extended defect. The observation of logarithmic capture mechanism further supports this speculation. On the other hand, no peak corresponding to the 0.23 eV level appears in isothermal DLTS spectra, which is possibly due to the severe temperature dependence of capture rate and the system's limitation in the high-frequency regime. For the sample with a V/III ratio of 50, only one dominant electron trap level, with an activation energy of 0.42 eV and a capture cross-section of 1.4×10−17 cm−2, is detected by isothermal DLTS method.

Deep level defects in both p + /n junctions and n-type Schottky GaN diodes are studied using the Fourier transform deep level transient spectroscopy. An electron trap level was detected in the range of energies at E c − E t =0.23–0.27 eV with a capture cross-section of the order of 10 −19 –10 −16 cm 2 for both the p + /n and n-type Schottky GaN diodes. For one set of p + /n diodes with a structure of Au/Pt/p + –GaN/n–GaN/n + –GaN/Ti/Al/Pd/Au and the n-type Schottky diodes, two other common electron traps are found at energy positions, E c − E t =0.53–0.56 eV and 0.79–0.82 eV. In addition, an electron trap level with energy position at E c − E t =1.07 eV and a capture cross-section of σ n =1.6×10 −13 cm 2 are detected for the n-type Schottky diodes. This trap level has not been previously reported in the literature. For the other set of p + /n diodes with a structure of Au/Ni/p + –GaN/n–GaN/n + –GaN/Ti/Al/Pd/Au, a prominent minority carrier (hole) trap level was also identified with an energy position at E t − E v =0.85 eV and a capture cross-section of σ n =8.1×10 −14 cm 2 . The 0.56 eV electron trap level observed in n-type Schottky diode and the 0.23 eV electron trap level detected in the p + /n diode with Ni/Au contact are attributed to the extended defects based on the observation of logarithmic capture kinetics.

The effect of doping on the steady-state photoconductivity, σ p , of hydrogenated amorphous silicon (a-Si:H) was explored down to temperatures of 4.2 K. Thermal quenching (TQ) is found in both n-type and p-type samples. The temperature of TQ decreases monotonically as the Fermi level is moved downward through the gap center. Electrons are the photocarriers below TQ and holes above TQ in undoped and p-type a-Si:H. A determination of type of photocarriers for hopping photoconductivity below 40 K yields electrons for n-type and holes for strongly p-type a-Si:H. The localization radii of localized conduction band tail states, a ∼ 13 A, and of valence band tail states, a ∼ 7 A, were determined from the dependence of the photocurrent on temperature and high electric fields. The temperature dependence of σ p of amorphous boron and boron carbon alloys is compared with those of other amorphous semiconductors.

The temperature TQ of thermal quenching of the photoconductivity σ p was found to increase monotonically as the Fermi energy is raised through the gap center from p-type to n-type hydrogenated amorphous silicon (a-Si:H). The sign of the majority photocarriers, determined from the magnitude of the drift mobility, changes with increasing T from negative at T TQ for both p- and n-type samples. By using subgap light, hv σ p / eG of electrons in n-type samples is 5 times larger than that of holes in p-type samples for T σ p at low T and in sufficiently strongly doped p-type samples the electron contribution is negligible.