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To get an in-depth insight into the arc erosion mechanism for tin dioxide-reinforced silver-based (Ag-SnO2) contact material, the contact pairs made of Ag-4wt%SnO2 contact material were, respectively, performed for 20,000 switching operations under the direct currents of 19 A and 29 A and the voltage of 12 V, together with the electrode gap of 4 mm. The eroded surfaces and cross-sectional morphologies and the chemical compositions were characterized by scanning electron microscopy equipped with an energy dispersive spectrometer (EDS). The results show that there is a deep erosion pit at the cathode and an apparent protrusion at the anode, suggesting that a serious material transfer generates from cathode to anode. The EDS results show that the Sn contents at the protrusion and at the region around the crater are below 0.75 wt.% and 4 wt.%, respectively. This reveals that SnO2 undergoes severe evaporation during electrical contact testing. Moreover, arc stability decreases with increasing the load current, and the Ag-SnO2 contact material has larger arc power (make arc: 68.2 J/s; break arc: 58.53 J/s at 29 A) as compared to Ag-TiB2 contact material (make arc: 62.85 J/s; break arc: 50.01 J/s at 29 A). As a result, it is thought that SnO2 evaporation reduces Ag dissipation, thus shortening the lasting time of the make arc. However, the emission current is increased owing to the low work function of SnO2, which further promotes the improvement in the density of the charged particles, thereby enhancing the arc power. Additionally, the large density of charged particles can sustain arc burning for a longer time, resulting in an extended break arc duration.

As a structural layer for microelectromechanical systems, in situ doped polycrystalline silicon germanium (poly-SiGe) can be deposited directly through openings of the uppermost dielectric onto the underlying metal interconnects to achieve electronic connections to the CMOS electronics. Differently from the existing works where poly-SiGe was deposited with the low pressure chemical vapor deposition (LPCVD), the plasma enhanced chemical vapor deposition (PECVD) method to produce poly-SiGe films forming the structural layer and the electrical contacts has been deployed. Compared with the films deposited with LPCVD, the as-deposited PECVD films formed contacts yielding low resistivity without any extra processing, such as precleaning and annealing. To investigate the contact resistance of poly-SiGe and polycrystalline germanium (poly-Ge) on titanium, Kelvin structures were fabricated and characterized. The substrate temperatures during the deposition were as low as 375°C for poly-SiGe and 340°C for poly-Ge, and low specific contact resistances of 3.2 × 10−6 O cm2 and 8.0 × 10−6 O cm2 respectively. This is expected to arise from the additionally acquired activation energies of ions from the plasma during PECVD. It is possibly due to the additional energies from the plasma, a titanium germanosilicide interfacial layer between poly-SiGe (or poly-Ge) and titanium (Ti) can be generated without high temperature processes. A metal stack was employed, to ensure a good adhesion, to block the diffusion and serve as an anti-reflection layer at the lithography.

Performance of low-temperature cascade thermoelectric coolers (TECs) is analyzed with emphasis on the deterioration of electrical contact resistance. Two key characteristics are under consideration: the maximum coefficient of performance at a given temperature difference and the maximum obtainable cooling for the TECs with fixed configuration. The deterioration of these characteristics with increasing of the resistance of electrical contacts is analyzed for the TECs having from two to six stages that are optimized to achieve the temperature differences of 100–150 K with minimal power consumption. The quality of electrical contacts is a crucial factor that greatly affects the performance of the cascade TECs. To maintain the TEC efficiency at an acceptable level, a contact resistance rc in the range from 10−7 Ω cm2 to 10−6 Ω cm2 should be provided, whereas with greater resistance, the TEC performance decreases dramatically, especially for the TECs with thermoelectric (TE) leg height of 0.5 mm and less. The irreversible losses caused by the resistance of the connecting metal strips are analyzed and the thicknesses that should provide an acceptably low rc level are determined for different cascade TECs with typical TE leg dimensions and spacing.

Nine metals (Ti, In, Ag, Sn, W, Mo, Sc, Zn, and Zr) have been investigated as electrical contacts to n-type single-crystal β-Ga2O3 substrates as a function of annealing temperature up to 800°C (in flowing Ar). For each contact metal, we investigated its electrical behavior and morphology at each annealing temperature, as well as the effects of adding a Au capping layer. Select metals displayed either ohmic (Ti and In) or pseudo-ohmic (Ag, Sn, and Zr) behavior under certain conditions; however, the morphology was often a problem. It was concluded that metal work function is not a dominant factor in forming an ohmic contact to β-Ga2O3 and that limited interfacial reactions play an important role.

A method to fabricate an electrode on a 110-nm-diameter Bi nanowire, encapsulated in a quartz template, was established using a dual beam instrument equipped with a focused ion beam and a scanning electron microscope. A fabrication method has already been successfully developed to obtain suitable Ohmic contact on both ends of Bi nanowires (several hundred nanometers in diameter) by first polishing the ends of the nanowires, and then depositing titanium/copper thin-films via an ion-plating method. However, with this method, it was difficult to obtain suitable electrodes on Bi nanowires with diameters less than 300 nm. Therefore, in order to understand why it was not possible to establish an electrical contact in small-diameter Bi nanowires, the vertical section of the fabricated electrode and the end of a 110-nm-diameter Bi nanowire were observed using a focused ion beam scanning electron microscope. A vacant area was observed between the end of the nanowire and the titanium thin-film, indicating a possible cause for the electrical contact failure. This implies that the quartz-encapsulated Bi nanowire is selectively removed when it undergoes polishing due to the great difference in hardness between Bi and quartz. A local electrode, which would connect the exposed area of the Bi nanowire and the metal thin-films on the surface of the quartz template, was fabricated by tungsten deposition using an electron beam. After fabrication of the opposite-end electrode by the same method, an electrical connection was successfully confirmed by measuring the voltage between both ends of the metal thin-films with a circuit tester. Ohmic contact was confirmed by measuring the current–voltage characteristics between the fabricated electrodes. As a result, the electrical resistivity and Seebeck coefficient were successfully measured at 300 K.

Nanofiber-sheet anisotropic conductive films (NS-ACFs) were invented to overcome the limitations of high joint resistance and short-circuit issues of ultra-fine-pitch interconnections. The NS-ACFs have great advantages in terms of suppressing conductive particle movement during the flip-chip bonding process. In a 20-μm ultra-fine-pitch with 7-μm bump spacing ultra-fine-pitch chip-on-glass assembly, suppression effects of conductive particle movement were significantly improved by using the NS-ACFs because an unmelted NS inside the ACFs suppressed the mobility of conductive particles so that they would not flow out during the bonding process. The NS-ACFs could significantly increase the capture rate of conductive particles from 31% up to 81% compared to conventional ACFs. Moreover, excellent electrical contact properties were obtained without melting the nanofiber material which was essential for the conventional nanofiber ACFs. The NS-ACFs are promising interconnection materials for ultra-fine-pitch packaging applications.

Miniature thermoelectric modules (TEMs) are required for micro power generation as well as local cooling, and they should have small size and high performance. However, conventional bulk TEMs generally have in-plane dimensions of a few centimeters, and empty space between the legs for electrical isolation makes efficient miniaturization difficult. In this study, a miniature TEM with footprint of about 0.35 cm2 and leg height of 0.97 mm was fabricated by reducing the dimensions of the legs and attaching them together to form a closely packed assembly, without using microelectromechanical processes. First, Bi0.4Sb1.6Te3 (BST) and Bi2Te2.7Se0.3 (BTS) ingots were made by ball milling and spark plasma sintering, and the ingots were cut into thin plates. These BST and BTS plates were then attached alternately using polyimide tapes, and the attached plates were sliced vertically to produce thin sheets. This process was repeated once again to make chessboard-like assemblies having 20 p–n pairs in an area of 0.35 cm2, and electrical contacts were formed by Ni sputtering and Ag paste coating. Finally, thermally conductive silicone pads (~500 μm) were attached on both sides of the assembly using electrically insulating interface thermal tapes (∼180 μm). The maximum output power (Pmax) from the miniature module was about 28 μW and 2.0 mW for temperature difference (ΔT) of 5.6°C and 50.5°C, respectively. Reducing the contact resistance was considered to be the key to increase the output power.

In this paper, the concept of an annular thermoelectric heat pump (ATEHP) has been introduced. An exoreversible thermodynamic model of the ATEHP considering the Thomson effect in conjunction with Peltier, Joule and Fourier heat conduction has been investigated using exergy analysis. New expressions for dimensionless heating power, optimum current at the maximum energy, exergy efficiency conditions and dimensionless irreversibilities in the ATEHP are derived. The results show that the heating power, energy and exergy efficiency of the ATEHP are lower than the flat-plate thermoelectric heat pump. The effects of annular shape parameter (Sr = r2/r1), dimensionless temperature ratio (θ = Th/Tc) and the electrical contact resistances on the heating power, energy/exergy efficiency of an ATEHP have been studied. This study will help in the designing of actual ATEHP systems.

Thermoelectrics is gaining increased attention as a renewable direct energy conversion method from heat to electricity. The most efficient and up-to-date thermoelectric materials for temperatures of up to 250°C are (Bi1−x Sb x )2 (Te1−y Se y )3 alloys. In the current research, to discover practical thermoelectric power generation devices capable of operation at such temperatures, Bi0.82Sb0.18 alloy was considered as a lead-free high-temperature (

A Harman-based instrument for the characterization of thermoelectric (TE) materials in a wide temperature range (the ZT-Scanner) was introduced in an earlier publication, with a focus on a two-sample system calibration (2SSC) procedure used for the precise evaluation of thermal losses during the measurements. This technique offers an option to accurately measure the main TE parameters from 300 K to 700 K. We now report the results of ZT-Scanner measurements of p-type Si80Ge20 polycrystalline samples, including the TE figure of merit ZT, Seebeck coefficient, and thermal and electrical conductivities. These samples proved to be extremely stable up to the maximum temperature of measurement, and could eventually serve as a standard for thermoelectric characterization. The measurements were performed using both PbSn solder and conductive silver paste contacts. In all cases, Ni plating was used as a protective barrier between the TE alloys and the contact material. The experimental data has been compared to the typical data measured by the Jet Propulsion Laboratory on similar samples, providing a quantitative estimation of the accuracy of the measurement system, which has been found to be better than 0.015, or 5%, up to 700 K for ZT. The consistency of the TE measurements is evaluated by means of a statistical analysis of repetitive tests on the same and on different samples of identical nature. We also analyze the influence of thermal and electrical contact resistance on the measured properties.

The development of a reliable technique for making good electrical contacts to semi-insulating (Cd,Mn)Te monocrystalline plates meant for x- and gamma radiation detectors, a technique of crystal surface preparation and a technique of passivation of the surfaces between electrodes were the main objectives of the studies. The investigations of the electrical contacts were focused on the amorphous/nanocrystalline contact layers. The effects of passivation of the inter-electrode surfaces on the magnitude of the surface leakage currents were studied.

This study investigated the effect of the boric oxide (B2O3) content on the arc-erosion performance of silver (Ag)-based composite electrical contact materials, produced by powder metallurgy combined with mechanical alloying. Pure Ag and B2O3 powders were milled in a high-energy planetary-type ball mill for 5 h, to obtain a powder mixture that would be used in manufacturing the composites. Powder mixtures containing 5, 10, and 15 vol.% B2O3 were drawn separately into a cylindrical die, pressed, and sintered at 200 MPa and 800°C. For each composition, a symmetrical contact pair configuration was created. Arc-erosion experiments were performed under the following testing conditions: operating voltage of 220 V, AC switching mode, frequency of 50 Hz, switching current of 5 A, and switching frequency of 60 operations/min. The relationship between the weight loss of the contacts and the number of cycles was investigated. Contact surfaces were examined by scanning electron microscopy (SEM). Chemical compositions near the arc were determined by energy-dispersive x-ray spectroscopy. The weight loss decreased with increasing B2O3 content up to 10 vol.%, indicating that the optimal arc-erosion performance (minimum weight loss) was obtained with 10 vol.% B2O3. Excessive B2O3 caused much more worn debris and increased the weight loss. SEM examinations of the contact surfaces showed that the size of the arc-affected zones generally increased with an increasing number of cycles.

A new high temperature thermoelectric device concept using large area nanostructured silicon p-type and n-type (PN) junctions is presented. In contrast to conventional thermoelectric generators, where the n-type and p-type semiconductors are connected electrically in series and thermally in parallel, we experimentally demonstrate a device concept in which a large area PN junction made from highly doped densified silicon nanoparticles is subject to a temperature gradient parallel to the PN interface. In the proposed device concept, the electrical contacts are made at the cold side eliminating the hot side substrate and difficulties that go along with high temperature electrical contacts. This concept allows temperature gradients greater than 300 K to be experimentally applied with hot side temperatures larger than 800 K. Electronic properties of the PN junctions and power output characterizations are presented. A fundamental working principle is discussed using a particle network model with temperature and electric fields as variables, and which considers electrical conductivity and thermal conductivity according to Fourier’s law, as well as Peltier and Seebeck effects.

Half-Heusler (HH) compounds are some of the most promising candidates among the medium-temperature thermoelectric materials being investigated for automotive and industrial waste heat recovery applications. For n- as well as p-type material, peak ZT values larger than one have been published recently, and first modules have been built. The next step to facilitate the industrialization of thermoelectric module production is upscaling of material synthesis. In this paper, the latest results of the thermoelectric properties of HH compounds produced in kg batches are presented and compared with values published in the literature. The performance of modules built from these materials is analyzed with respect to power output and long-term stability of the material and electrical contacts.

Contact resistance gains prominence as feature size reduces to the nanometer length scale. This work studies the effects of electrical contact resistance on the performance of silicon nanowire-based thermoelectric coolers using COMSOL Multiphysics. The values of the contact resistance used to simulate the impact are experimentally extracted from a pair of thermoelectric legs with each leg made of top-down-fabricated 100 silicon nanowires having diameter of 100 nm. Analytical models agreeing well with the simulation results are provided. Lastly, a design methodology is proposed for optimum performance in on-chip cooling applications.

Five metals with large work functions including Co, Ni, Cr, Ti, and Mo and two silicides including MnSi and TiSi2 were examined to determine the best contact material for the thermoelectric material higher manganese silicide (HMS). Three-layer structures of HMS/contact/HMS were prepared in a sintering process. The contact resistance was measured versus temperature. The structures were subjected to x-ray diffraction and energy-dispersive x-ray spectroscopy examination. Thermal stability of the structures was determined by heating the samples to 700°C for different time intervals. The pure metals failed to make reliable contacts due to poor mechanical and chemical stability at high temperatures. In contrast, the metal silicides (MnSi and TiSi2) showed superior chemical and mechanical stability after the thermal stability test. The observed contact resistance of MnSi and TiSi2 was within the range of practical interest (10−5 Ω cm2 to 10−4 Ω cm2) over the entire range of investigated temperatures (20°C to 700°C). The best properties were found for the nanograined MnSi, for which the resistance of the contact was as low as 10−6 Ω cm2.

Four-wire resistance measurements were performed using a bismuth nanowire, 750 nm in diameter, 1.96 mm in length, and encapsulated in a quartz template. One side of the quartz template was polished to allow focused ion beam (FIB) processing, and metal film layers were deposited on the polished side to form electrodes. Nanofabrication was employed to remove a selected portion of the quartz, and FIB processing was used to expose the surface of the bismuth nanowire. A local area of the bismuth wire was successfully exposed, and a carbon electrode was deposited on the bismuth wire in situ by a chemical reaction between the ion beam and phenanthrene gas. Additional carbon deposition on the initial carbon electrode was used to connect to a metal film on the quartz template. In total, four nanofabrications were performed on the bismuth wire to create the desired electrical contacts. The resistivity of the nanowire was measured by a four-wire method to be 1.29 μΩ m at 300 K, corresponding to that of bulk bismuth. The temperature dependence of the resistivity was also measured, and was qualitatively and quantitatively in good agreement with previous calculated and experimental results using other bismuth nanowires. The present results demonstrate the successful development of a technique to fabricate an electrode on a local area of a nanowire using FIB processing to form suitable electrical contacts.

Three methods for attaching electrodes to a bismuth nanowire sample were investigated. In the first and second methods, thin layers of titanium and copper were deposited by ion plating under vacuum onto the edge surface of individual bismuth nanowire samples that were encapsulated in a quartz template. Good electrical contact between the electrodes and the nanowire was achieved using silver epoxy and conventional solder on the thin-film layers in the first and second methods, respectively. In the third method, a low-melting-point solder was utilized and was also successful in achieving good electrical contact in air atmosphere. The connection methods showed no difference in terms of resistivity temperature dependence or Seebeck coefficient. The third method has an advantage in that nanocontact is easily achieved; however, diffusion of the solder into the nanowire allows contamination near the melting point of the solder. In the first and second methods, the thin-film layer enabled electrical contact to be more safely achieved than the direct contact used in the third method, because the thin-film layer prevented diffusion of binder components.

In this work, the effects of the degree of cure on the electrical and mechanical behavior of an anisotropic conductive film (ACF) were investigated. The degree of cure of the ACF as a function of bonding time was quantified by dynamic differential scanning calorimetry (DSC) study and attenuated total reflectance/Fourier-transform infrared (ATR/FT-IR) analysis. According to the results, the thickness expansion rate of the ACF as a function of temperature decreased and the storage modulus increased as the degree of cure increased. In addition, the contraction stress of a partially cured ACF with a degree of cure below 40% was much smaller than that of an ACF with a degree of cure above 90%. The ACF contact resistance decreased and the ACF peel adhesion strength increased as the degree of cure of the ACF increased. In particular, poor electrical contact was observed when the degree of cure was below 40%. The ultimate tensile strength (UTS) increased as the degree of cure increased and was closely related to the peel adhesion strength. Furthermore, ACF joints with a degree of cure below 40% had higher contact resistance than those with a degree of cure above 90% during 85°C/85% relative humidity testing.

The Cu/SnAg double-bump structure is a promising candidate for fine-pitch flip-chip applications. In this study, the interfacial reactions of Cu (60 μm)/SnAg (20 μm) double-bump flip chip assemblies with a 100 μm pitch were investigated. Two types of thermal treatments, multiple reflows and thermal aging, were performed to evaluate the thermal reliability of Cu/SnAg flip-chip assemblies on organic printed circuit boards (PCBs). After these thermal treatments, the resulting intermetallic compounds (IMCs) were identified with scanning electron microscopy (SEM), and the contact resistance was measured using a daisy-chain and a four-point Kelvin structure. Several types of intermetallic compounds form at the Cu column/SnAg solder interface and the SnAg solder/Ni pad interface. In the case of flip-chip samples reflowed at 250°C and 280°C, Cu 6 Sn 5 and (Cu, Ni) 6 Sn 5 IMCs were found at the Cu/SnAg and SnAg/Ni interfaces, respectively. In addition, an abnormal Ag 3 Sn phase was detected inside the SnAg solder. However, no changes were found in the electrical contact resistance in spite of severe IMC formation in the SnAg solder after five reflows. In thermally aged flip-chip samples, Cu 6 Sn 5 and Cu 3 Sn IMCs were found at the Cu/SnAg interface, and (Cu, Ni) 6 Sn 5 IMCs were found at the SnAg/Ni interface. However, Ag 3 Sn IMCs were not observed, even for longer aging times and higher temperatures. The growth of Cu 3 Sn IMCs at the Cu/SnAg interface was found to lead to the formation of Kirkendall voids inside the Cu 3 Sn IMCs and linked voids within the Cu 3 Sn/Cu column interfaces. These voids became more evident when the aging time and temperature increased. The contact resistance was found to be nearly unchanged after 2000 h at 125°C, but increases slightly at 150°C, and a number of Cu/SnAg joints failed after 2000 h. This failure was caused by a reduction in the contact area due to the formation of Kirkendall and linked voids at the Cu column/Cu 3 Sn IMC interface.

The electrical characteristics of organic (3,4-polyethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) contacts to HgCdTe are studied as a potential alternative to metal/HgCdTe contacts. The use of organic PEDOT:PSS contacts offers the potential for an improved contact technology for HgCdTe IR detector arrays. In this work, PEDOT:PSS contacts are deposited on n-type and p-type HgCdTe epilayers by spin coating and patterned using a metal mask. Current-voltage (I-V) characteristics are measured on these contacts, showing nearly ohmic behavior. The temperature dependence of I-V characteristics (T = 40-300 K) shows increased resistance for decreasing temperature, consistent with the temperature dependence of HgCdTe resistivity, suggesting that the I-V characteristics are primarily dominated by the HgCdTe material.

The hygrothermal stability of electrical contacts made from silver and graphite electrically conductive pastes is comparatively evaluated by measurement of the increase in contact electrical resistance during immersion in water at 15°C and 40°C. The pastes are silver paint, silver paint with a nonconductive epoxy overcoat, silver epoxy, and graphite colloid. Each electrical contact is made between a seven-strand tin-coated copper wire and the surface of a carbon fiber epoxy-matrix composite. Silver paint and graphite colloid penetrate the spaces among the 130-μm-diameter strands, but silver epoxy does not. Partly due to its low penetrability and the silver flake (15 μm) preferred orientation, silver epoxy gives contacts of significantly higher resistance than silver paint. Graphite colloid is comparable to silver epoxy in the resistance. Among the four pastes, silver paint with an epoxy overcoat is most durable, though it gives slightly higher resistance than silver paint without epoxy. Silver epoxy is less durable than silver paint without an epoxy overcoat, particularly at 40°C, due to the low hygrothermal stability of epoxy. Graphite colloid is even less durable than silver epoxy, due to its being water based.

The electrical properties of several metal contacts to n-type ZnO (0001) were studied. The ZnO samples consisted of bulk single-crystal material, epitaxial layers on sapphire grown by molecular beam epitaxy (MBE), and polycrystalline thin films on sapphire obtained by pulsed laser deposition (PLD). Ohmic and rectifying contacts were observed dependent upon both the metal material and the ZnO surface. Ohmic contacts were characterized using the circular transmission line method (c-TLM), where contact resistivity was found to be in the range of 10−4−10−5 Ω-cm2. Schottky behavior was observed using Ag contacts exhibiting varying leakage current and breakdown voltage dependent on the polarity of the ZnO surface.

Pressure and pressureless electrical contacts were evaluated by measuring the contact electrical resistivity between copper mating surfaces. Pressure electrical contacts with a contact resistivity of 2×10−5 Ω·cm2 have been attained using a carbon black paste of a thickness of less than 25 μm as the interface material. In contrast, a pressureless contact with silver paint as the interface material exhibits a higher resistivity of 3×10−5 Ω·cm2 or above. A pressureless contact with colloidal graphite as the interface material exhibits the same high contact resistivity (1×10−4 Ω·cm2) as a pressure contact without any interface material. On the other hand, pressureless contacts involving solder and silver epoxy exhibit lower contact resistivity than carbon black pressure contacts.

This paper reports the anomalous scaling effect of tungsten/titanium nitride/titanium to (a) n+ and (b) p+ silicon electrical contact resistance in dynamic random access memory (DRAM) devices, upon post heat treatment following rapid thermal silicidation annealing. The electrical measurements on contacts of sizes ranging from 0.54 μm to 0.18 μm reveal that the increase in resistance becomes larger as the contact size decreases. Transmission electron microscopy (TEM) results show that the silicide film agglomeration proceeds more severely as the contact size decreases. To explain the size-dependent degradation of the contact resistance, numerical simulation of the shape evolution of the silicide film is performed. The results show that the poor film coverage, especially at the edge, accelerates the reduction rate in contact area.

The history of power electronic semiconductor devices is reviewed that leads to a discussion of new materials. The wide bandgap and good thermal conductivity of SiC permit its use at high temperatures, and the high electric field breakdown is favorable for high power devices. However, there remain a number of key problems with SiC semiconductor technology that must be solved before reliable production can begin. Difficulties with the insulator-to-SiC interface, SiC epitaxial material, passivation, doping, and stability of contacts drive viable device structures. One issue, the formation of electrical contacts, is described in more detail. In particular, the impact of SiC preparation procedures, surface roughness, and deposition conditions are discussed, e.g., variations in the chemical cleaning process affect the removal of overlayers and/or the roughneing of the SiC surface. Studies have shown that this cleaning or etching step can in turn affect device performance. At present, fabrication of the best quality contacts is interlinked with other material problems, and even to obtain adequately low resistivities, constraints are placed on the processing of devices.

We report on a contacting and fabrication scheme for a sub-500 nm InAs/AlSb/GaSb resonant interband tunneling diode (RITD) without using any fine-line lithography. Epitaxial regrowth on patterned substrates combined with sidewall spacer technology is used to define the device dimensions. During regrowth, the crystal facet termination obtained by choosing the appropriate orientation for the device is utilized to make electrical contact to the device in the desired directions and to isolate the device in all other directions. The concept, fabrication process, current-voltage characteristics of the device, and a comparison with RITDs fabricated in a conventional manner are reported.

Ternary phase diagrams have proven valuable for understanding the reactions between a metal contact and a compound semiconductor, as well as for choosing thermally stable electrical contacts in thermodynamic equilibrium with the semiconductor. Since InP is important for both optoelectronic and electronic devices, the metal-In-P systems are of particular interest. In this work, new portions of isothermal sections of the (Rh, Ir, Ru, Os)-In-P diagrams are presented. Then, since no compilation of the published metal-In-P phase diagrams is available, the diagrams are reviewed here. The features of these diagrams are discussed in terms of the thermodynamics of the metal-In-P systems, particularly the considerable thermodynamic stability of many of the transition metal phosphides. Finally, some of the phases in thermodynamic equilibrium with InP, particularly PdIn and Ni2P, are highlighted for their potential for high-temperature contacts to InP.

High quality electrical contacts to GaN are required for the advancement of electronic and optoelectronic devices based on the III-V nitrides. In this study, the metallurgy of contacts to GaN and the implications for the design of electrical contacts are considered. First, phase diagrams are estimated for the transition metal-Ga-N systems. The diagrams are then used as an aid in predicting the reaction products of annealed metal/GaN contacts, to suggest materials that may be useful as thermally stable electrical contacts and to explore the role of the partial pressure of N2 in the annealing environment on the reactions in metal/GaN contacts. It is believed that this information will be particularly useful to researchers during the early stages of contact development since very little experimental information is currently available on the GaN contact metallurgy.

The reverse bias break-down voltage and resistance of Au and Ag contacts sputter deposited on nitrogen doped p-type ZnSe, having free hole concentrations in the low to mid 1017 cm−3 range, have been studied. Samples were heat treated over the range of 150—400°C for times of 15—45 min. The minimum break-down voltage for the Au contacts (3.0 V) was found to occur following heat treatments at 350—400°C for 30 min and for Ag contacts (2.3 V) following heat treatments at 150°C for 45 min. Secondary ion mass spectrometry and Auger electron spectroscopy were used to identify changes in the contacts induced by heat treatments. No evidence was found for the formation of new interfacial compounds, but Au diffused into the ZnSe at T >350°C. The data suggest that conduction through the Au/ZnSe contacts was dominated by avalanche breakdown assisted by deep acceptor levels formed by the diffusion of Au into the ZnSe. The results from the Ag contacts suggest that interfacial O forms a highly doped region in the ZnSe leading to conduction dominated by field emission currents.

The current-voltage characteristics of electric contacts made of different materials on p-type ZnSe that form Schottky barriers from 0.3 to 1.2 eV are studied theoretically using the formula $$J = \frac{{A^* T}}{k}\int_0^\infty {T(E)[F(E) - F(E - eV)]dE,} $$ where T(E) is the energy-dependent quantum tunneling probability and F(E) is the Fermi distribution function. The contribution to the total current of both the thermionic emission and the tunneling are therefore included. The net doping concentrations under study range from 1.0×1017 cm−3 to 1.0×1019 cm−3. The reverse bias voltage across the barrier at a current density of 200 A/cm2 is used to assess whether the barrier is reduced to an ohmic contact. A barrier of 0.3 eV is already an ohmic contact at doping concentration p=1.0×1017 cm−3, while a barrier of 1.2 eV still behaves like a diode event at p=1.0×1019 cm−3.

The effect of rapid thermally nitrided titanium films contacting silicided (titanium disilicided) and nonsilicided junctions has been studied in the temperature range of 800 to 900°C. The rapid thermal nitridation of titanium films used as diffusion barriers between aluminum and silicon, has a major impact on shallow junction complementary metal oxide semiconductor technologies. During the process of rapid thermal nitridation, the dopants in the junctions undergo a redistribution and affect the electrical properties of shallow junction structures. This work focuses on using novel contact resistance structures to measure the variation in electrical parameters for rapid thermally nitrided titanium films annealed at different temperatures. The self-aligned silicide (salicide) junctions in this study were formed using rapid thermally annealed titanium films. Electrical contact resistance testers were used to measure the interface contact resistance between the salicide and silicon, as well as between the metal and the salicide. The results show that the interface contact resistance to the p− diffused salicided junctions increases with rapid thermal nitridation of the additional titanium film, whereas the interface contact resistance to the n− diffused salicided junction shows a decrease. Further, as a function of the rapid thermal annealing temperature (for fixed titanium thickness), the nonsalicided diffusions show an increase in the interface contact resistance. The boron profiles at the TiSi2/Si interface obtained using secondary ion mass spectroscopy show an excellent qualitative agreement with the electrical results for each of the conditions discussed. The films were also characterized using Rutherford back-scattering spectrometry and transmission electron microscopy and the results show good agreement with the measured variation in electrical parameters. These results also show that as the anneal temperature is increased, the TiN thickness increases, further the change in the silicide/silicon interface position with the nitridation of the additional titanium layer was verified.

An investigation is made into the possibility of providing low resistance contacts to shallow junction InP devices which do not require sintering and which do not cause device degradation even when subjected to extended annealing at elevated temperatures. We show that the addition of In to Au contacts in amounts that exceed the solid solubility limit lowers the as-fabricated (unsintered) contact resistivityR c to the 10-5 ohm-cm2 range. If the In content is made to correspond exactly to that required to form the intermediate compound Au9ln4, then the contacts so formed are stable, both electrically and metallurgically, even after extended annealing (12 hr) at 400° C. We next consider the contact system Au/Au2P3 which has been shown to exhibit as-fabricatedR c values in the 10-6 ohm-cm2 range, but which fails quickly when heated. We show that the substitution of a refractory metal (W, Ta) for Au preserves the lowR c values while preventing the destructive reactions that would normally take place in this system at high temperatures. We show, finally, thatR c values in the 10 ohm-cm2 range can be achievedwithout sintering by combining the effects of In or Ga additions to Au contacts with the effects of introducing a thin Au2P3 layer at the metal-InP interface.

We have studied the effects of In doping on the structural and electrical properties of a liquid phase epitaxially (LPE) grown GaAs. The results of surface morphology studies show that macroscopically, a terrace-free area in certain regions can be seen on the surface of a GaAs layer doped with In of 2.4 × 1019 cm3. The full widths at half-maximum (FWHM) of x-ray double crystal rocking curves show that a GaAs epi-layer of good crystalline quality can be obtained by doping In to a concentration up to 4.3 × 1019 cm-3, beyond which a sharp increase in the FWHM is observed. Etch pit density (EPD) study also shows that the dislocation density is reduced by doping the epi-layer with In. At an optimum In concentration, 2.4 × 1019 cm-3, the EPD was reduced by a factor of 20 when measured at the surface of a 9μm thick epi-layer. The I-V characteristics of Au-GaAs Schottky diodes show, for the layer with an optimal In concentration, an ideality factor close to 1.04 over more than seven decades of current. For the same layer, the reverse I-V characteristics are close to an ideal Schottky diode and could be fitted by a theoretical curve, combining the thermionic field emission and thermionic emission. For doping levels higher than 6 × 1019 cm-3, the epitaxial layer quality deteriorated. We report the results obtained from the Nomarski optical microscope, double crystal x-ray rocking curves, etch pit density, forward and reverse I-V characteristics, and the theoretical current transport models.

Electrical contacts have been formed on n-type GaAs (1.8 x 1018 carriers cm−3) using evaporated layers of 26 nm Ge/18 nm Ni or 40 nm Ge, with bombardment by 100-140 keV Se+ ions. After bombardment, the samples were annealed and the contact areas were subsequently coated, by evaporation, with Au for the Ge/Ni contacts or Ni + Au for the Ge contacts and then subjected to further thermal annealing. The objective is to induce ion beam mixing between Ni-Ge-GaAs or Ge-GaAs whilst simultaneously forming a heavily doped n-type region beneath the contact. The ion beam processing has been carried out for doses of 1014−1016 cm−2 at temperatures ranging from 300-723K, followed by annealing at 693K for 120s for the Ge/Ni contacts and up to 1143K for the Ge contacts. In order to separate the doping effects from the ion beam mixing, bombardments were also undertaken using Kr+ ions. The specific contact resistance has been measured and the contacts further analysed using Auger depth profiling and RBS analysis. The contact morphology has been determined by SEM measurements.

A new method of forming electrical contacts on high purity p-type silicon has been developed. The resultant contacts are ohmic from 18 to 300K. The electrical sparking technique permits localized doping in the contact region of the device while avoiding the over-all high annealing temperatures required by diffusion. Indium solder is used for metallization and attachment of wires to the sparked regions. The process is simple and easily applied to samples for measuring electrical transport properties or to devices, such as silicon solar cells.

Heterojunction solar cells (HJSC’s), fabricated by electron beam evaportaion of SnO2 films onto monocrystalline and polycrystalline Si substrates, show conversion efficiencies as high as 9.9%, fill factors of 0.64, and open circuit voltages of 525 mV under AMI simulated irradiation. The SnO2, an n-type semiconductor, acts as a transparent window to solar irradiation and as an antireflection coating of the Si, and it provides the band bending in the Si necessary for photovoltaic conversion. The SnO2 films, nominally 50 nm thick, have conductivities of the order of 103(Ω-cm)−1 so that the film makes a good electrical contact between the junction and the metallic front contacts. Measurements of C−2-V and I-V characteristics are consistent with heterojunction theory, and the data imply an electron affinity of the SnO2 of approximately 0.8 eV greater than the electron affinity of Si. This value limits the open circuit voltage of HJSC’s made on p-type substrates to values too small for useful photovoltaic conversion. The predominant dark current mechanism of units of n-type substrates at room temperature and forward bias in the range of 0.3−0.5 V is electron-hole recombination in the transition region. The experimentally determined activation energy is 0.51 eV, approximately Eg/2. At forward voltages below 0.3 V, multistep tunneling via interband states predominates. The photocurrent apparently depends on interface states through which the photogenerated holes in the Si recombine with electrons in the SnO2.

A method that enables accurate determination of contact resistances in thermoelectric generators and which gives detailed insight into how these reduce module performance is presented in this paper. To understand the importance taking thermal and electrical contact resistances into account in analysis of thermoelectric generators, full-scale modules were studied. Contact resistances were determined by means of non-linear regression analysis on the basis of results from 3D finite element simulations and experiments in a setup in which heat flow, voltage, and current were measured. Statistical evaluation showed that the model and the identified contact resistances enabled excellent prediction of performance over the entire range of operating conditions. It was shown that if contact resistances were not included in the analysis the simulations significantly over-predicted both heat flow and electric power output, and it was concluded that contact resistance should always be included in module simulations. The method presented in this paper gives detailed insight into how thermoelectric modules perform in general, and also enables prediction of potential improvement in module performance by reduction of contact resistances.

We report a method for minimization of the surface leakage current and reduction of the time-dependent degradation of (Cd,Mn)Te, a material under consideration for semiconductor X-ray and Gamma-ray detector applications. Preliminary characterization of the resistivity of the plates was achieved by use of an EU-ρ-μτ-SCAN. For semi-insulating samples the resistivity was in the range 108–109 Ω-cm. Electrical contacts were made on the lower and upper surfaces of each sample. After protection of the contacts, lateral surfaces were subjected to reaction with a variety of chemical substances. Subsequent chemical treatments of (Cd,Mn)Te single crystal platelets were studied to optimize passivation of the inter-electrode surfaces. The control voltage–current (I–V) characteristics were measured repeatedly at hourly and daily intervals. It was found that chemical etching in 10%Br-MeOH, then 1%Br-MeOH, and finally passivating the surfaces of the crystals with (NH4)2S reduces the surface leakage current.