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Bismuth antimony telluride (Bi0.5Sb1.5Te3) is a ternary compound with good thermoelectric properties at near room temperature. In this research, Bi0.5Sb1.5Te3 powders were hydrothermally synthesized at different temperatures (100, 150, 190, and 230°C) for 24 h. The deposition procedure of Bi0.5Sb1.5Te3 thin films was done by using thermal evaporation. The phases and microstructures of powders and thin films were investigated by x-ray diffraction and field emission scanning electron microscopy. Moreover, the size distribution of powders was investigated using a particle size analyzer. The phase and microstructural results of the different synthesized powders confirmed that the Bi0.5Sb1.5Te3 thin film prepared by powder synthesis at 150°C for 24 h is the best choice for manufacturing with good thermoelectric properties because of its nano-sized grains and high purity. The results showed that the Bi0.5Sb1.5Te3 thin film fabricated by powders synthesized at 150°C has a single rhombohedral phase with a good semiconductor performance. The results of thermoelectric tests confirmed that the Bi0.5Sb1.5Te3 thin film fabricated using a hydrothermal method and thermal evaporation deposition approach shows a high Seebeck coefficient (183.5 μV/K) and low electronic thermal conductivity (1.32 × 10−4 W/m k−1) at 298 K. Besides, the power factor values of 0.7, 2.59 and 2.9 μW/cm K−2 were obtained at 298, 373 K and 473 K, respectively.

The magnesium-rich intermetallic ternary compound NdNiMg15 in space group P-4/nmm (no. 26) space group in trigonal phase is studied theoretically using hybrid functional theory (HP-B3PW91) in the density functional theory (DFT) framework. The calculation results are in good agreement with experimental data. The metallic nature of the compound is estimated from the electronic properties. The magnetic as well as metallic character of the compound is due to the Nd 4f electrons. The title compound exhibits good conductivity as revealed by the thermoelectric analysis. The magnetic phase of the material indicates its stability within the G-type antiferromagnetic phase (G-AFM), governed by direct Nd–Nd exchange interactions with a magnetic moment of 3.57µB/Nd per unit cell. The AFM phase of the studied compound is also confirmed by post-DFT measurements at TN = 8.15 K as well as θ = −2.5 K. The antiferromagnetic nature of this compound could enable its use in magnetic probes to read data stored in antiferromagnetic moments while leaving them unaffected by disturbing magnetic fields.

A ternary compound of Li6NiNb2O9 with a rock-salt structure was prepared by the conventional mixed oxide route, and after the ceramic preparation processes, its microwave dielectric properties were investigated. Ceramics with a single phase and a rock-salt crystal structure can be obtained under our optimized sintering conditions, and a disordered rock-salt structure for Li6NiNb2O9 compound can be confirmed by the Rietveld method. Relatively dense microstructures can be obtained under the sintering conditions of 1080°C/2.0 h, with microwave dielectric properties of e = 13.5, Q × f = 20,600 GHz (9.4 GHz) and τf = −33.9 ppm/°C. Although decomposition of such phase occurred when high sintering temperature was applied (> 1100°C), the density and microwave dielectric properties of the ceramics showed anomalous increases.

The Pb-Se-Sn ternary system is of interest to thermoelectric applications. Nevertheless, no phase diagram exists for the entire compositional regime at any temperature. Ternary Pb-Se-Sn alloys are equilibrated at 350°C and 500°C, and their equilibrium phases are determined. The isothermal sections of the equilibrium Pb-Se-Sn phase diagram at 350°C and 500°C are proposed based on the phase diagrams of the three constituent binary systems and ternary phase equilibria results in the literature and those determined in this study. No ternary compound is found. The phase relationships are similar at 350°C and 500°C. At both temperatures, binary compounds, α-PbSe and γ-SeSn, have very significant ternary solubility, but the ternary solubility of Pb in the Se2Sn phase is negligible. There are still unresolved questions about the type and shape of the liquid phase at the Se corner.

The microstructure of the Er-Fe-V ternary system at 773 K was investigated by means of x-ray diffraction analysis and scanning electron microscopy. The isothermal section at 773 K was obtained, consisting of 9 single-phase regions, 15 two-phase regions, and 8 three-phase regions. The homogeneity range of the ternary compound ErFe12−xVx was determined to be x = 1.1 to 2.6. The maximum solid solubility of V in Fe, ErFe2, and Er2Fe17 was found to be about 13.0 at.%, 5.3 at.%, and 2.5 at.%, respectively. The maximum solid solubility of Fe in V was found to be about 25 at.%. Regarding the microwave absorbing properties of V-doped Er2Fe17 alloy, the absorption peak of the Er2Fe17−xVx alloys moved toward the low frequency region while the minimal reflection loss decreased upon V addition, with absorption frequency bandwidth (R

Natural and synthetic tetrahedrites are currently the focus of attention in thermoelectricity due to their abundance, numerous possibilities of substitution, and their complex crystal structure ( $$ I\bar{4}3m $$ ) resulting in extremely low lattice thermal conductivity (below 1 W m−1 K−1 above 300 K). Here, we report on the synthesis, structural and chemical characterizations, and high-temperature thermoelectric properties of polycrystalline Cu12−x M x Sb4−y Te y S13 (M = Zn, Ni) tetrahedrites. Upon substituting on both the Cu and Sb sites, we successfully improved the thermoelectric properties with respect to the ternary compound Cu12Sb4S13 with peak ZT values of 0.7 at 700 K.

The photocurrent (PC) of hot-wall-epitaxy-grown BaIn2S4 layers was studied at different temperatures and for different photoresponse intensities. With increasing temperature, the position of the PC spectra tended to shift toward longer wavelength. These PC peaks corresponded to band-to-band transitions caused by intrinsic transitions from the valence band states to the conduction band states. Also, the bandgap variations were well matched by the equation E g(T) = E g(0) − 3.79 × 10−3 T 2/(T + 499), where E g(0) was estimated to be 3.0597 eV, 3.2301 eV, and 3.2606 eV for transitions corresponding to the valence band states Γ 4(z), Γ 5(x), and Γ 5(y), respectively. By use of the selection rule and results from the PC spectroscopy, the crystal field and the spin–orbit splitting were found to be 0.1703 and 0.0306 eV, respectively. Thus, the PC intensity gradually decreased with decreasing temperature. The decrease of PC intensity was caused by the presence of trapping centers associated with native defects in the BaIn2S4 layers. The trap level was found to be a shallow donor-level type of 20.4 meV, 1.6 meV below the conduction band. Consequently, these trap levels, which are related to native defects in BaIn2S4 layers, are believed to limit PC intensity with decreasing temperature.

Interfacial reactions in Sn/Ni–4.5 wt.%Si and Sn–Cu/Ni–4.5 wt.%Si couples at 250°C, and Sn–Ni–Si ternary phase equilibria at 250°C were investigated in this study. Ni–Si alloys, which are nonmagnetic, can be regarded as a diffusion barrier layer material in flip chip packaging. Solder/Ni–4.5 wt.%Si interfacial reactions are crucial to the reliability of soldered joints. Phase equilibria information is essential for development of solder/Ni–Si materials. No ternary compound is present in the Sn–Ni–Si ternary system at 250°C. Extended solubility of Si in the phases Ni3Sn2 and Ni3Sn is 3.8 and 6.1 at.%, respectively. As more Si dissolves in these phases their lattice constants decrease. No noticeable ternary solubility is observed for the other intermetallics. Interfacial reactions in solder/Ni–4.5 wt.%Si are similar to those for solder/Ni. Si does not alter the reaction phases. No Si solubility in the reaction phases was detected, although rates of growth of the reaction phases were reduced. Because the alloy Ni–4.5 wt.%Si reacts more slowly with solders than pure Ni, the Ni–4.5 wt.%Si alloy could be a potential new diffusion barrier layer material for flip chip packaging.

The ternary compound Cs2Hg6S7 has shown considerable promise as a wide gap semiconductor for hard radiation detection at room temperature. We report on the measurement of defect levels in Cs2Hg6S7 using photo-induced current transient spectroscopy. We observe a series of defect levels with mean activation energies of 0.053, 0.052, 0.34, 0.35, and 0.46 eV. The defects are attributed to Cs vacancies and Cs and Hg antisite defects. Defect capture cross-sections are in the range 10−20–10−15 cm2.

Alloys based on Sn and Sn-Ag are commonly used as Pb-free solders, and Ni is frequently used in barrier layers. Co has been studied as a possible alloying element in both solders and barrier layers. Thus, the Sn-Co-Ni and Sn-Ag-Co-Ni alloy systems are important for electronic soldering. Forty-nine Sn-Co-Ni alloys and 24 Sn-rich Sn-Ag-Co-Ni alloys were prepared. The primary solidification phases of these as-cast alloys were determined, and based on these results and the available phase diagrams of the constituent systems, the liquidus projections of Sn-Co-Ni ternary and Sn-Ag-Co-Ni quaternary systems at 90 at.% and 95 at.% Sn were determined. In the Sn-Co-Ni system, no ternary compound was found; (Ni,Co)3Sn2 and (Ni,Co) are continuous solid solutions, and there are eight kinds of primary solidification phases: Sn, CoSn3, CoSn2, CoSn, (Ni,Co)3Sn2, (Ni,Co), Ni3Sn, and Ni3Sn4. In the 90 at.% and 95 at.% Sn isoplethal sections of the Sn-Ag-Co-Ni liquidus projection, the primary solidification phases are CoSn2, CoSn, Ni3Sn4, and Ag3Sn.

This work revealed that the Cu-deficient ternary compounds Cu3−xSbSe4 free of Te and Pb exhibit enhanced thermoelectric performance. Cu3−xSbSe4 (x = 0, 0.025, 0.050, 0.075) polycrystalline materials with high phase purity were fabricated by a facile method combining mechanical alloying and spark plasma sintering. Effects of Cu deficiencies on crystal structures, microstructures, element chemical states, and thermoelectric properties were systematically studied. High carrier concentration was obtained for the compositions Cu2.95SbSe4 and Cu2.925SbSe4 due to additional Cu vacancies, contributing to a remarkable increase in electrical conductivity. Together with a satisfactorily large Seebeck coefficient above 300 μV/K, a high power factor of about 890 μW/m-K2 at 523 K was achieved for Cu2.95SbSe4 and Cu2.925SbSe4, almost 60% larger than that of the stoichiometric sample with x = 0. The maximum ZT value was increased to 0.50 at 673 K in the Cu2.925SbSe4 sample sintered at a high temperature (703 K); this is the highest value reported so far for the undoped Cu3SbSe4 system.

This study examined the interfacial reactions between liquid Sn-Zn alloys and Co substrates at 250°C with different Zn compositions from 1 wt.% to 9 wt.%. The reaction phases formed at the interface were significantly affected by the Zn content. One irregular reaction phase, γ2-CoZn13, was observed in the Sn-9 wt.%Zn/Co reaction. Decreasing to 7 wt.% Zn, the interfacial product changed to the γ1 phase. After a longer reaction time, a new ternary compound with composition Sn-20.2 at.%Zn-31.4 at.%Co, the T phase, was formed between the γ1 phase and Co substrate. Only one very thin and continuous T phase layer was found, and it was stable at the Sn-4 wt.%Zn/Co interface, even after 120 h reaction. However, the Sn-3 wt.%Zn/Co couples revealed significant microstructural evolution in both the T and CoSn3 layers. Moreover, the dominant phase became CoSn3 as the Zn content decreased below 2 wt.%. Based on these interfacial results, a predicted Sn-Zn-Co phase diagram (less than 30 at.% Co) at 250°C is proposed. The corresponding reaction paths of these couples are illustrated on the phase diagram.

We report the thermoelectric properties of Mn-doped Cu2MnxSn1−xSe3 compound, with x ranging from 0.005 to 0.1 at temperature ranging from 80 K to 723 K. All samples maintain cubic zincblende-like structure, and no impurity phase was detected. The electrical resistivity decreases rapidly when Mn4+ replaces Sn2+ in the matrix. The excess Mn impurities in the x = 0.05 and x = 0.1 samples also affect the Seebeck coefficient. The total thermal conductivity is increased for Mn-doped samples except for the x = 0.005 sample. In all, both power factor and figure of merit are improved by Mn doping over the entire temperature range. The ZT value of the x = 0.02 sample reaches 0.035 at 300 K, and for x = 0.01 reaches 0.41 at 716 K, which are comparable to the best thermoelectric performance for ternary Cu-based compounds.

The isothermal section of the Ni-Sn-Zn ternary system at 500°C was investigated by means of x-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive spectrometry (SEM/EDS). A new ternary compound with a composition of Ni36Sn42Zn22 (in at.%) was discovered in the present study. The space group of this compound is P\( \overline{\textit{4}}\)3m with lattice parameter a = 0.88283(4) nm. Two ternary phases, i.e., τ1 and τ2, which are derived from α′-Ni3Sn2 and β-NiZn, respectively, were observed to be present at 500°C. The solubility of Sn in Ni2Zn11 was determined to be about 3.5 at.%, and that of Zn in Ni3Sn to be about 5 at.%.

To optimize the thermoelectric properties of Si2Ti-type Al32Mn34Si34 (C54-phase), which possesses a large absolute Seebeck coefficient |S| exceeding 300 μV/K with negative sign, we partially substituted Cr and Fe for Mn, and succeeded in decreasing the number of valence electrons (in the case of Cr) without observing precipitation of secondary phases. A large, positive Seebeck coefficient exceeding 200 μV/K was observed for Al32CrxMn34−xSi34 (1 ≤ x ≤ 2.5), which consists almost solely of the C54-phase. The increase of hole concentration caused by Cr substitution for Mn was confirmed by both the reduction in electrical resistivity and the sign reversal of the Seebeck coefficient. The largest ZT-value for positive Seebeck coefficient (p-type behavior) was obtained for Al32Cr2.5Mn31.5Si34, with the resulting ZT-value reaching a magnitude twice as large as the largest ZT-value of the ternary compound Al33Mn34Si33 possessing p-type behavior.

The growth mechanism of an interfacial (Cu,Ni)6Sn5 compound at the Sn(Cu) solder/Ni(P) interface under thermal aging has been studied in this work. The activation energy for the formation of the (Cu,Ni)6Sn5 compound for cases of Sn-3Cu/Ni(P), Sn-1.8Cu/Ni(P), and Sn-0.7Cu/Ni(P) was calculated to be 28.02 kJ/mol, 28.64 kJ/mol, and 29.97 kJ/mol, respectively. The obtained activation energy for the growth of the (Cu,Ni)6Sn5 compound layer was found to be close to the activation energy for Cu diffusion in Sn (33.02 kJ/mol). Therefore, the controlling step for formation of the ternary (Cu,Ni)6Sn5 layer could be Cu diffusion in the Sn(Cu) solder matrix.

The process of SnPb immersion in Ag/Cu coated light emitting diode lead frames (LED LFs) (alloy 42) was investigated. SnPb solder was found to cause dewetting of the LF substrate after 6 s of immersion. We believed that the dewetting of the SnPb solder could be attributed to spalling of the interfacial compound grains. The addition of a small amount of Ni to the molten SnPb solder (0.1 wt.%) retarded that spalling and helped to prevent dewetting. The mechanisms for spalling retardation by the addition of Ni additives are as follows: (1) the Ni additives slow down the reaction rate between the molten SnPb solder and the Ag/Cu plating layer; (2) the Ni additives participate in interfacial reactions to form (Cu,Ni) 6 Sn 5 ternary compounds, which are more stable than binary compounds and have a slower ripening process.

The influence of current direction on the Cu-Ni cross-interaction in the Cu/Sn/Ni joint configuration was investigated in this study. During current stressing, an electric current towards or away from the Ni-side of Cu/Sn/Ni was imposed at 150°C. It was observed that the (Cu,Ni)6Sn5 ternary compound was the dominant reaction product at both interfaces, and its growth at the Ni-side strongly depended upon the direction and magnitude of the electron flow. When the electron flow was towards the Ni-side, more Cu was found to be driven to the Ni-side, resulting in an increase in the thickness of (Cu,Ni)6Sn5. This is due to the chemical-potential-induced Cu flux ( $$ J_{\rm{chem}}^{\rm{Cu}} $$ ) that was enhanced by the electromigration ( $$ J_{\rm{em}}^{\rm{Cu}} $$ ). In the case of electron flow away from the Ni-side, the supply of Cu to the Ni-side was retarded due to the fact that $$ J_{\rm{em}}^{\rm{Cu}} $$ was in the opposite direction to $$ J_{\rm{chem}}^{\rm{Cu}} . $$ The results of this study revealed that the Ni-side (Cu,Ni)6Sn5 thickness remained almost unchanged under current stressing of 104 A/cm2 at 150°C, which suggests the inward Cu flux is approximately equal to the outward flux, i.e., $$ J_{\rm{chem}}^{\rm{Cu}} \approx J_{\rm{em}}^{\rm{Cu}} . $$

Phase relationships in the Au-Co-Sn ternary system have been thermodynamically assessed by using the CALPHAD technique. The existing thermodynamic descriptions of the binary Au-Sn and Co-Sn systems were improved by incorporating the ab initio calculated enthalpies of formation of the intermetallic compounds including AuSn, CoSn, AuSn2, and AuSn4. For consistency, the Au-Co system was reassessed on the basis of the same pure element data as adopted for the Au-Sn and Co-Sn systems. With the combination of the three binary descriptions, the Au-Co-Sn ternary system was assessed by taking into account the ternary solubility in the binary compounds and the formation of a ternary compound. The obtained set of thermodynamic parameters can reproduce the measured phase equilibria at 380°C. The isothermal section at 396°C, the CoSn-Au and Au-SnCo vertical sections, and the liquidus projection were also calculated.

Due to the use of phosphorus-containing nickel substrates in microelectronics, understanding of their reaction with Sn-based solders and knowledge of the corresponding reaction products is highly important. Therefore the ternary Ni-P-Sn system was investigated experimentally using x-ray diffraction (XRD), scanning electron microscopy (SEM) + energy dispersive x-ray spectroscopy (EDX)/wavelength-dispersive x-ray spectroscopy (WDS), and differential thermal analysis (DTA). Sample preparation was done by alloying powders of the starting components contained in alumina crucibles in evacuated quartz tubes. In this study the phase equilibria in the Ni-rich part of the ternary Ni-P-Sn system are described in the form of three partial isothermal sections at 550°C, 700°C, and 850°C. A total of five ternary compounds exist in the Ni-rich part, and the binary Ni3Sn2 HT phase was found to dissolve 17.6 at.% P at 850°C. This well agrees with literature reports, while a different extent and shape of the large homogeneity range of this phase were found. Between 850°C and 700°C phase equilibria change significantly due to the formation of the ternary phases Ni10P3Sn5 (T3), Ni13P3Sn8 (T4), and Ni2PSn (T5). © 2009 TMS.

Sn-In alloys are promising low-melting-point Pb-free solders. Knowledge of the ternary Sn-In-Cu liquidus projection is important for Sn-In solder applications. Sn-In-Cu ternary alloys were prepared and their primary solidification phases and phase-transformation temperatures during heating were determined. The liquidus projection of the Sn-In-Cu ternary system was determined based on the primary solidification phase at different compositional regimes, the phase-transformation temperatures of the ternary alloys, the phase boundaries and reaction temperatures of the constituent binary systems, and the available ternary Sn-In-Cu data in the literature. No ternary compound was found in the as-cast alloys. The Sn-In-Cu liquidus projection has 11 primary solidification phase regions and seven ternary invariant reactions with the liquid phase, and η-(Cu6Sn5,Cu2In) has a very large compositional regime as the primary solidification phase. A very interesting phenomenon that was also observed is that the solidification paths of some Sn-In-Cu alloys surpass the liquidus trough after their intersections.

The solid-state, cross-interaction between the Ni layer on the component side and the Cu pad on the printed circuit board (PCB) side in ball grid array (BGA) solder joints was investigated by employing Ni(15 μm)/Sn(65 μm)/Cu ternary diffusion couples. The ternary diffusion couples were prepared by sequentially electroplating Sn and Ni on a Cu foil and were aged isothermally at 150, 180, and 200°C. The growth of the intermetallic compound (IMC) layer on the Ni side was coupled with that on the Cu side by the mass flux across the Sn layer that was caused by the difference in the Ni content between the (Cu1−x Ni x )6Sn5 layer on the Ni side and the (Cu1−y Ni y )6Sn5 layer on the Cu side. As the consequence of the coupling, the growth rate of the (Cu1−x Ni x )6 Sn5 layer on the Ni side was rapidly accelerated by decreasing Sn layer thickness and increasing aging temperature. Owing to the cross-interaction with the top Ni layer, the growth rate of the (Cu1−y Ni y )6Sn5 layer on the Cu side was accelerated at 150°C and 180°C but was retarded at 200°C, while the growth rate of the Cu3Sn layer was always retarded. The growth kinetic model proposed in an attempt to interpret the experimental results was able to reproduce qualitatively all of the important experimental observations pertaining to the growth of the IMC layers in the Ni/Sn/Cu diffusion couple.

The mutual interaction between Sn/Ni and Sn/Cu interfacial reactions in a Ni/Sn/Cu sandwich sample has been studied. The major interfacial reaction product on the Cu side was Cu6Sn5, while on the Ni side, a ternary (Cu,Ni)6Sn5 compound layer was formed. We found that the growth kinetics of the interfacial compound layers on both sides reached a steady state in the late reflow stage. The interfacial compound layer on the Cu side retained a constant thickness. On the other hand, the interfacial compound layer on the Ni side grew at a relatively fast rate, which was found to be linear with time. Our results indicate that the growth of the ternary (Cu,Ni)6Sn5 compound layer was controlled by the Cu dissolution flux at the solder/Cu6Sn5 compound interface. The dissolution constant of the Cu6Sn5 compound into the molten Sn was determined to be 0.13 μm/s.

The Leti-Lir has studied II–VI compounds for infrared (IR) detection for more than 20 years. The need to reduce the production cost of IR focal plane arrays (FPAs) sparked the development of heteroepitaxy on large-area substrates. Germanium has been chosen as the heterosubstrate for the third generation of IR detectors. First, we report on the progress achieved in HgCdTe growth on 3-in. and 4-in. (211)B CdTe/Ge. Then, we discuss the choice of a new machine for larger size and better homogeneity. Finally, we present the latest results on third-generation IR multicolor and megapixel devices. First-time results regarding a middle wavelength infrared (MWIR) dual-band FPA, with a reduced pitch of 25 µm, and a MWIR 1,280×1,024 FPA will be shown. Both detectors are based on molecular beam epitaxy (MBE)-grown HgCdTe on Ge. The results shown validate the choice of Ge as the substrate for third-generation detectors.

In this study, we investigated the effects of gamma radiation on ZnS/CdTe-passivated HgCdTe photodiodes that were fabricated with one of two different surface treatments using bromine, Br2, or hydrazine, N2H4. Unlike the ZnS-passivated HgCdTe photodiodes, the ZnS/CdTe-passivated HgCdTe photodiodes showed no degradation in resistance-area product at zero bias (R0A) values after gamma irradiation of up to 1 Mrad. However, there is a significant difference between the bromine- and hydrazine-treated samples. Regardless of the dose of gamma radiation, there was little change in the forward current characteristics of the hydrazine-treated diode in comparison with the conventional bromine-treated diode. The hydrazine-treated diode showed fairly uniform R0A values of >107 Ω-cm2 up to 1 Mrad of gamma irradiation, whereas the bromine-treated diode showed an abrupt change in R0A values from ∼106 Ω-cm2 to ∼107 Ω-cm2 after gamma irradiation. Therefore, for use in a gamma radiation environment, the best combination for high-performance HgCdTe photodiodes is a ZnS/CdTe passivant that has been treated with hydrazine.

The negative luminescence (NL) efficiency of a 5 mm×5 mm array (100% effective fill factor) of HgCdTe photodiodes (λco=4.8 µm at 295 K) has been measured as a function of temperature. The internal NL efficiency of ≈95% at λ=4 µm is nearly independent of temperature in the 240–300 K range and, at 300 K, corresponds to an apparent temperature reduction of 60 K. This performance is obtained at a reverse-bias saturation-current density of only 0.11 A/cm2 at 296 K. With large area, high efficiency, and low saturation-current density, our results demonstrate a level of NL device performance at which such applications as cold shields for large-format focal plane arrays (FPAs) and multipoint nonuniformity correctors appear practical.

The recently developed Te-rich, liquid-phase-epitaxy growth technology for low arsenic-doped mid-wavelength infrared (MWIR) HgCdTe with p-type doping concentrations

Intentionally undoped and three different, doped layer structures are used to investigate properties of AlGaN/GaN high electron mobility transistors (HEMTs) before and after SiN passivation. For unpassivated devices, the drain current, transconductance, cutoff frequency, and microwave output-power increase with increased doping level, in spite of an increase in the gate-leakage current. After passivation, an overall performance improvement of all devices occurs. The passivation-induced sheet charge decreases from 2×1012 cm−2 in undoped structures to ∼0.7×1012 cm−2 in higher doped structures and performance improvement with passivation is less pronounced for higher doped devices. However, the output power of unpassivated and passivated devices on higher doped structures is much higher than that on the undoped-passivated counter-part. These results underline an advantage of the doped layer structure for the preparation of high-performance AlGaN/GaN HEMTs.

Two-dimensional, midwavelength infrared (MWIR) HgCdTe detector arrays have been fabricated using reactive ion etching (RIE). Detector-to-detector uniformity has been studied in the devices fabricated with CdTe- and ZnS-passivation layers. Mapping of the doping profile, passivant/HgCdTe interface electrical properties, and diode impedance-area product (R0Aj) in a two-dimensional array of diodes has been carried out. Temperature and perimeter/area dependence of the dark current are studied to identify the bulk and surface current components. Maximum R0Aj=2×107 Θcm2 was achieved in CdTe-passivated, 200×200 µm2 diode arrays. It demonstrates that CdTe-passivated, RIE-processed HgCdTe is a feasible technology.

We discuss buffer-layer concepts for the synthesis of low defect-density HgCdTe epilayers on Si for both hybrid and monolithically integrated, infrared focal-plane arrays (IRFPAa). The primary technical problems to overcome include the 19% lattice-parameter mismatch between HgCdTe and Si, and the (211)B surface orientation required for molecular-beam epitaxy (MBE), the growth technique of choice for HgCdTe. We provide a general overview of IRFPAs, motivations for realizing HgCdTe on Si, the current state-of-the-art parameters as a baseline, and three novel buffer-layer concepts and technologies based on (1) obedient GeSi films on SiO2, (2) wafer bonding, and (3) chalcogenides.

We have investigated the negative luminescence properties of a midwave-infrared (MWIR) HgCdTe photodiode (λco = 5.3 µm at 295 K) grown on a silicon substrate. The internal negative luminescence efficiencies measured using a self-referencing optical technique were 88% throughout the 3–5 µm spectral region and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction of 53 K at room temperature and 35 K at 240 K. Efficiencies measured by an electrical modulation technique were consistent with the measured internal efficiencies and the measured reflectivity of the device. This is the highest efficiency and largest apparent reduction in temperature reported to date, and slightly higher than that measured earlier for photodiodes grown on CdZnTe despite a longer cut-off wavelength. These results provide further indication that the HgCdTe/Si photovoltaic device technology is capable of combining high quality with high yield.

The reactive ion etching (RIE) technique has been shown to produce high-performance n-on-p junctions by localized-type conversion of p-type mid-wavelength infrared (MWIR) HgCdTe material. This paper presents variable area analysis of n-on-p HgCdTe test diodes and data on two-dimensional (2-D) arrays fabricated by RIE. All devices were fabricated on x = 0.30 to 0.31 liquid-phase epitaxy (LPE) grown p-type (p = ∼1 × 1016 cm−3) HgCdTe wafers obtained from Fermionics Corp. The diameter of the circular test diodes varied from 50 µm to 600 µm. The 8 × 8 arrays comprised of 50 µm × 50 µm devices on a 100-µm pitch, and all devices were passivated with 5000 A of thermally deposited CdTe. At temperatures >145 K, all devices are diffusion limited; at lower temperatures, generation-recombination (G-R) current dominates. At the lowest measurement temperature (77 K), the onset of tunneling can be observed. At 77 K, the value of 1/R0A for large devices shows quadratic dependence on the junction perimeter/area ratio (P/A), indicating the effect of surface leakage current at the junction perimeter, and gives an extracted bulk value for R0A of 2.8 × 107 Ω cm2. The 1/R0A versus P/A at 195 K exhibits the well-known linear dependence that extrapolates to a bulk value for R0A of 17.5 Ω cm2. Measurements at 77 K on the small 8 × 8 test arrays were found to demonstrate very good uniformity with an average R0A = 1.9 × 106 Ω cm2 with 0° field of view and D* = 2.7 × 1011cm Hz1/2/W with 60° field of view looking at 300 K background.

We report on the first successful growth of the ternary-alloy CdSexTe1−x(211) on 3-in. Si(211) substrates using molecular-beam epitaxy (MBE). The growth of CdSeTe was performed using a compound CdTe effusion source and an elemental Se effusion source. The alloy composition (x) of the CdSexTe1−x ternary compound was controlled through the Se:CdTe flux ratios. Our results indicated that the crystalline quality of CdSeTe decreases as the alloy composition increases, which is possibly due to an alloy-disordering effect. A similar trend was observed for the CdZnTe ternary-alloy system. However, the alloy-disordering effect in CdSeTe was found to be less severe than that in CdZnTe. We have carried out the growth of CdSeTe on Si at different temperatures. An optimized growth window was established for CdSeTe on Si(211) to achieve high-crystalline-quality CdSeTe/Si layers with 4% Se. The as-grown layers exhibited excellent surface morphology, low surface-defect density (less than 500 cm−2), and low x-ray full width at half maximum (FWHM) values near 100 arcsec. Additionally, the CdSeTe/Si layer exhibited excellent lateral uniformity and the best etched-pit density (EPD) value on a 4% CdSeTe, measured to be as low as 1.4 × 105 cm−2.

HgCdTe detector performance and yield are strongly dependant on CdZnTe substrate and HgCdTe epilayer properties, and on key device processes, especially for 8–12 µm application. Due to the correlation and optimization between these figures and diode performance, AIM has developed a mature HgCdTe technology for superior detector performance and high production rate. To meet high yield and performance for long wavelength (LW) HgCdTe diodes, dislocation densities of < 1 × 10t cm−2 both in substrate and epilayer have to be ensured. By a unique AIM substrate growth process, dislocation densities of 2 × 104-9 × 104 cm−2 are achieved for all substrates and epilayers (100% yield). The etch pit density (EPD) on 〈111〉 epilayers is revealed by an AIM proprietary etching procedure. One critical effect is the dislocations in the diode area, which can originate from the substrate and epilayer growth and the subsequent device processes, respectively. Our studies have shown that device processes can cause additional dislocations in the diode area. Diode yield was clearly improved by a combination of wet and dry etching for diode contact etching.

Device performance and defects in AlGaN/GaN high-electron mobility transistors (HEMTs) have been correlated. Surface depressions and threading dislocations, revealed by optical-defect mapping and atomic force microscopy (AFM), compromised the effectiveness of the SiNx surface-passivation effect as evidenced by the gate-lag measurements. The residual carriers in the GaN-buffer layer observed from the capacitance-voltage depth profile have been attributed to the point defects and threading dislocations either acting as donors or causing local charge accumulations. Deep-level transient-spectroscopy measurements showed the existence of several traps corresponding to surface states and bulk-dislocation defects. The formation of electron-accumulation regions on the surface or (and) in the GaN-buffer layer was confirmed by currentvoltage measurements. This second, virtual gate formed by electron accumulations can deplete the channel and cause a large-signal gain collapse leading to degraded output power. A good correlation was established between the device performance and defects in AlGaN/GaN HEMT structure.

High-quality InGaN/GaN multiple-quantum well (MQW) light-emitting diode (LED) structures were prepared by a temperature-ramping method during metal-organic chemical-vapor deposition (MOCVD) growth. Two photoluminescence (PL) peaks, one originating from well-sensitive emission and one originating from an InGaN quasi-wetting layer on the GaN-barrier surface, were observed at room temperature (RT). The observation of high-order double-crystal x-ray diffraction (DCXRD) satellite peaks indicates that the interfaces between InGaN-well layers and GaN-barrier layers were not degraded as we increased the growth temperature of the GaN-barrier layers. With a 20-mA and 160-mA current injection, it was found that the output power could reach 2.2 mW and 8.9 mW, respectively. Furthermore, it was found that the reliability of the fabricated green LEDs prepared by temperature ramping was also reasonably good.

Nitride-based light-emitting diodes (LEDs) with a reflector at the backside of the sapphire substrates have been demonstrated. It was found that an SiO2/TiO2 distributed-Bragg reflector (DBR) structure could reflect more downward-emitting photons than an Al-mirror layer. It was also found that the 20-mA output power was 2.76 mW, 2.65 mW, and 2.45 mW for the DBR LED, Al-reflector LED, and conventional LED, respectively. With the same 50-mA current injection, the integrated-electroluminescence (EL) intensity of a DBR LED and an Al-reflector LED was 19% and 15% larger than that observed from a conventional LED.

The effects of various elements of substrate metallization, namely, Au, Ni, and P, on the solder/under-bump metallization (UBM), (Al/Ni(V)/Cu) interfacial reactions in flip-chip packages during multiple reflow processes were systematically investigated. It was found that Au and P had negligible effects on the liquid-solid interfacial reactions. However, Ni in the substrate metallization greatly accelerated the interfacial reactions at chip side and degraded the thermal stability of the UBM through formation of a (Cu,Ni)6Sn5 ternary compound at the solder/UBM interface. This phenomenon can be explained in terms of enhanced grain-boundary grooving on (Cu,Ni)6Sn5 in the molten solder during the reflow process. This could eventually cause the rapid spalling of an intermetallic compound (IMC) from the solder/UBM interface and early failure of the packages. Our results showed that formation of multicomponent intermetallics, such as (Cu,Ni)6Sn5 or (Ni,Cu)3Sn4, at the solder/UBM interface is detrimental to the solder-joint reliability.

Cadmium telluride (CdTe) is being widely used for passivating the HgCdTe p-n diode junction. Instead of CdTe, we tried a compositionally graded HgCdTe as a passivation layer that was formed by annealing an HgCdTe p-n junction in a Cd/Hg atmosphere. During annealing, Cd diffuses into HgCdTe from the Cd vapor, while Hg diffuses out from HgCdTe, forming compositionally graded HgCdTe at the surface. The Cd mole fraction at the surface was constant regardless of the annealing temperature in the range of 250-350°C. Capacitance versus voltage (C-V) curves for p-type HgCdTe that were passivated with compositionally graded HgCdTe formed by Cd/Hg annealing at 260°C showed a smaller flat-band voltage than the one passivated by thermally deposited CdTe, indicative of the better quality of the passivation. A long-wave infrared (LWIR) HgCdTe p-n junction diode passivated by compositionally graded HgCdTe showed about a one order of magnitude smaller RdA value than the one passivated by thermally deposited CdTe, confirming the effectiveness of the compositionally graded HgCdTe as a passivant.

State-of-the-art large-area photovoltaic (PV) detectors fabricated in HgCdTe grown by molecular beam epitaxy (MBE) have been demonstrated for the Crosstrack Infrared Sounder (CrIS) instrument. Large-area devices (1 mm in diameter) yielded excellent electrical and optical performance operating at 81 K for λc ∼ 15 µm, at 98 K for λc ∼ 9 µm, and λc ∼ 5-µm spectral cutoffs. Fabricated detectors have near-theoretical electrical performance, and Anti Reflection coated quantum efficiency (QE) is greater than 0.70. Measured average RoA at 98 K is 2.0E7 Ωcm2, and near-theoretical QEs greater than 0.90 were obtained on detectors with λc ∼ 5-µm spectral cutoffs. These state-of-the-art large-area PV detector results reflect high-quality HgCdTe grown by MBE on CdZnTe substrates in all three spectral bands of interest.

In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors (HBTs) were grown metamorphically on GaAs substrates by molecular beam epitaxy. In these growths, InAlAs, AlGaAsSb, and InP metamorphic buffer layers were investigated. The InAlAs and AlGaAsSb buffer layers had linear compositional grading while the InP buffer layer used direct binary deposition. The transistors grown on these three layers showed similar characteristics. Bulk thermal conductivities of 10.5, 8.4, and 16.1 W/m K were measured for the InAlAs, AlGaAsSb, and InP buffer layers, as compared to the 69 W/m K bulk thermal conductivity of bulk InP. Calculations of the resulting HBT junction temperature strongly suggest that InP metamorphic buffer layers should be employed for metamorphic HBTs operating at high power densities.

NiInGe ohmic contact materials, which are attractive to use in future GaAs devices, were previously developed in our laboratories. Although the NiInGe contacts provided low contact resistances of about 0.3 Ω-mm and excellent thermal stability, further reduction of the contact resistance (RC) of the NiInGe contacts was mandatory to use these contacts in submicron devices. In this paper, the microstructural parameters, which influence the RC values, were investigated by correlating the RC values with the microstructure at the interface between the contact materials and the GaAs substrate. The RC values of the NiInGe contacts were found to depend strongly on the volume fraction and the In concentration (x) of the InxGa1−xAs compound semiconductor layers, which were formed at the metal/GaAs interface. Both the volume fraction and the In concentration of the InxGa1−xAs layers were found to depend on the thickness of the In layer used in the NiInGe contact and the annealing temperature to form the ohmic contact. A RC value of 0.18 Ω-mm was obtained for the Ni (18 nm)/In (13 nm)/Ge (30 nm) contact (where a slash “/” indicates the deposition sequence) after annealing at temperature of 650°C for 5 sec.

The phase equilibria of the Cu-In-Sn system were investigated by means of the diffusion couple method, differential scanning calorimetry (DSC) and metallography. The isothermal sections at 110–900 C, as well as vertical sections at 10wt.%Cu–70wt.%Cu were determined. It was found that there are large solubilities of In in the e(Cu3Sn), δ(Cu41Sn11), and η phases in the Cu-Sn system, and large solubilities of Sn in the γ, η, and δ(Cu7In3) phases in the Cu-In system. The η phase was found to continuously form from the Cu-In side to the Cu-Sn side, and a ternary compound (Cu2In3Sn) was found to exist at 110 C. Thermodynamic assessment of the Cu-In-Sn system was also carried out based on experimental data of activity and phase equilibria using the CALPHAD method, in which the Gibbs energies of the liquid, fcc and bcc phases are described by the subregular solution model and that of compounds, including two ternary compounds, are represented by the sublattice model. The thermodynamic parameters for describing the phase equilibria were optimized, and agreement between the calculated and experimental results was obtained.

The results of wafer fusion between GaAs and InP followed by transfer of an InGaAs film from the InP to GaAs substrate are presented in this paper. This technique of film transfer allowed the subsequent growth of epitaxial materials with approximately 7% lattice mismatch. Type-II InAs/GaInSb superlattices photodetectors of different designs have been grown by molecular beam epitaxy (MBE) on the alternative InGaAs/GaAs substrate and on standard GaSb substrates. Comparison between photodetectors grown on the two different substrates with nearly identical superlattice periods showed a shift in the cut-off wavelength. The superlattices grown on the alternative substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb substrates.

The reactions between the eutectic PbSn solder and the Au/Ni/Cu tri-layer metallization in advanced microelectronic packages were studied. In this investigation, reflowed packages were subjected to aging at 160°C for times as long as 4000 h. Immediately after the reflow, all the Au had left the Au/Ni/Cu metallization, forming many (Au1−xNix)Sn4 particles distributed throughout the whole solderjoint. In addition, there was a thin layer of Ni3Sn4 (1.4 μm) at the interface. After 500 h of aging, most of the (Au1−xNix)Sn4 particles regrouped at the interface as a continuous (Au0.45Ni0.55)Sn4, layer over the Ni3Sn4 layer. After 2500 h of aging, nearly all the Ni layer had been consumed. A 15 μm layer of (Au0.45Ni0.55) Sn4 and a 20 μm Ni3Sn4 were found over the remaining Ni. At 3000 h, the Cu had started to react with both Ni3Sn4 and (Au1−xNix)Sn4, forming a layer of (Cu1−p−pAupNiq)6Sn5, a layer of (Cu1−r−sAu1Nis)6Sn5, and a layer of Cu3Sn over the Cu layer. A small amount of Cu (2.7–5.7 at.%) was found to dissolve in this Ni3Sn4, forming a ternary compound (Ni1−yCuy)3Sn4. It was revealed that Au diffused up-hill during the reaction. After aging for 4000 h, all the (Au1−xNix)Sn4 had disappeared and Au atoms had diffused into the (Cu1−p−qAupNiq)6Sn5 and (Cu1−r−sAurNis)6Sn5 phases. The practical implications for the above findings were pointed out in this paper.

Recent work has shown that a Au−Ni−Sn ternary compound with a nominal composition of Au0.5Ni0.5Sn4 redeposits and grows at the interface between eutectic Pb−Sn solder and Ni/Au metallization during aging at 150°C. The present work verifies the existence of the Au0.5Ni0.5Sn4 phase by examining the Sn-rich corner of the Au−Ni−Sn ternary phase diagram. The reconfiguration mechanism of the AuSn4 from the bulk solder is also discussed, with detailed observations of the Au0.5Ni0.5Sn4 microstructure. The results show that the Ni solubility limit in the AuSn4 phase is approximately 12 at.% at 150°C and thus, the Au0.5Ni0.5Sn4 phase is a ternary AuSn4-based compound with high Ni solubility. Due to the slight solubility and the fast diffusion of Au in the eutectic Pb−Sn at 150°C, the AuSn4 intermetallics in the bulk solder can reconfigure to form a AuxNi1−xSn4 compound at the interface where Ni is available. The AuxNi1−xSn4 compound layer consists of nanocrystals arranged in a larger grainlike morphology. It appears that the inherent lattice strain of the AuxNi1−xSn4 compound and the volume change due to its formation results in a nanocrystalline microstructure.

In this letter, we report the effect of UV-ozone treatments on the electrical characteristics of InGaAs/InP heterostructure bipolar transistors (HBTs). For treatments of less than 10 min, the HBT’s current gain increased with the UV-ozone exposure. This improvement is attributed to a passivation of the extrinsic base. For exposures longer than 10 min, the current gain is reduced. An increase of the base collector leakage current, leading to a degradation of the HBT’s breakdown voltage, was observed after only about 2 min of UV-ozone treatment.

Au/Ni metallization has become increasingly common in microelectronic packaging when Cu pads are joined with Pb-Sn solder. Recent work has shown that a ternary compound with stoichiometry Au0.5Ni0.5Sn4 redeposits onto the interface during aging, compromising the strength of the joint. In the present work the growth of the Au0.5Ni0.5Sn4 layer is documented and methods for inhibiting its growth were investigated. It was determined that multiple reflows, both with and without additional aging, can substantially limit the thickness of the ternary layer.