The quantum correction of the Einstein relation for high frequencies

For nondegenerate semiconductors the low-frequency Einstein relation qD₀ = kTμ₀ must be replaced by qD′(ω) = kTμ′(ω)p(ω) at high frequencies, where D′ and μ′ are the real parts of the complex diffusion coefficient D and the mobility μ, respectively, and p(ω) is the quantum correction factor for thermal noise. This is shown, first by treating thermal noise as a case of velocity-fluctuation noise, and secondly by using a simple statistical model. The results are extended to degenerate semiconductors and metals.     

Raman spectroscopy study of the carbon structure of <Emphasis Type="Italic">a</Emphasis>-C:(H,Cu) and <Emphasis Type="Italic">a</Emphasis>-C:(H,Co) composite films

The main changes induced in the Raman spectrum of a-C:H films in the 1200-to 1700-cm^?1 frequency region by modification with Cu and Co are ascertained. A comparison of the results obtained with the available data on various carbon structures reveals that the introduction of metals in concentrations comparable to the carbon content stimulates growth and ordering of graphite-like nanoclusters in the sp² carbon bonding system. It is found that, while similar structural rearrangements occur under thermal annealing of both a-C:H and composite a-C:(H, Cu) and a-C:(H, Co) films, the presence of metals interferes with thermally stimulated graphitization. The size of the graphite-like nanoclusters in annealed and unannealed films of all types is estimated, and Co is shown to produce a more efficient graphitizing effect than Cu.     

Thermal conductivity and the Wiedemann-Franz relation in melts of indium and gallium antimonides

The thermal and electrical conductivities of indium and gallium antimonides were studied in both solid and liquid states. It is shown that the calculated values of the Lorentz number (L) in InSb and GaSb, unlike in metals, increase with increasing temperature after melting. An anomalous increase in L is consistent with anomalous (for melts) temperature dependences of density, viscosity, and coordination number of these melts at the same temperatures.     

Effect of reactive sputter etching of SiO2 on the properties of subsequently formed MOS systems

We investigated the effects of reactive sputter etching (RSE) of SiO₂ on the electrical properties of the SiSiO₂ system using CHF₃ in a commercial apparatus. SIMS and Auger spectrometry revealed contamination of RSE-exposed Si surfaces with carbon and heavy metals. The generation of crystal defects during thermal reoxidation was observed to be closely related to the level of metal contamination. C-V, C-t and I-V measurements on subsequently formed MOS structures showed, that oxide charge, interface state and mobile ion densities are nearly unaffected by the RSE process. However, minority carrier lifetime in the Si substrate and isolation behavior of the oxide layer are strongly degraded; our results suggest, that both effects are mainly due to metallic impurities. The use of inert cathode materials like quartz reduces metal contamination, but a non-negligible contribution from the grounded metal surfaces of the reactor remains. Carrier lifetime and insulating properties reach the values obtained on wet chemically etched samples only after extended times of plasma excitation in the apparatus. This is attributed to a passivation of the grounded surfaces by the formation of polymer films. Taking advantage of this effect MOSFETs were fabricated by the use of RSE without deterioration of their electrical performance.     

Metal evaporation dependent charge injection in organic transistors

To illuminate a long-term remaining issue on how contact metallization (metal and speed) affects charge injection, we investigated top-contact pentacene transistors using two categories of metals deposited at various rates. Differing from previous studies such as those devoted to morphological influences by microscopy, in this work we concentrated on their electrical characteristics in particular combining the low-frequency noise which provided a direct quantity of trap density and its evolution with respect to contact metal and deposition rate. It turns out that the transistors with noble metal (Au) suffer from metal-diffusion related charge trapping in the pentacene bulk close to the Au/pentacene interface, and this diffusion-limited injection is greatly tuned from bulk to interface by speeding Au deposition which leads to a Schottky-like injection due to the severe thermal damage to the upper pentacene layer. Applying a conventional contacting metal (Cu), however, Ohmic contacts with much fewer traps are always observed regardless of metallization speed. This is attributed to an ultra-thin interlayer of Cu_xO that guarantees stable Ohmic injection by introducing gap states and protecting the pentacene film so that those transistors appear to be free from Cu metallization. Our results quantitatively show the limiting factors of charge injection for different metals and at various evaporation rates.     

Rapid thermal alloyed ohmic contact on inp

The results of a study of the electrical and metallurgical properties of thin metallic layers deposited on InP for use as an ohmic contact are presented. A rapid thermal annealing system was used to alloy AuGe/Ni/Au contacts ton-type ion implanted InP. Rutherford backscattering and contact resistivity measurement were used to evaluate the structural and electrical characteristics of these rapid thermal alloyed thin films. Varying degrees of mixing between the metals and the semiconductor were found depending on the temperature and temperature-time cycle. These results were compared to furnace and graphite strip-heater alloying techniques. A correlation between the interface structure and the contact resistance was found. Temperatures between 430 and 450° C and alloying time of 2 sec have produced the best electrical results, with specific contact resistance as low as 2*10^?7 Ω cm² on semi-insulating InP which was Siimplanted with a peak concentration about 2*10¹⁸ cm^?3. The optimum alloy temperature is marked by the onset of substantial wrinkling of the contact surface, whereas essentially smooth surfaces are obtained at temperatures below optimum. The depth of the alloyed ohmic contact is controlled by the time of heating and could be less than 1000Å.     

Theoretical models for work function control (Invited Paper)

We have studied Fermi level pinning (FLP) of Hf-based high-k gate stacks based on thermodynamics based on an O vacancy model. Our study shows that FLP cannot be avoided when the system is under thermal equilibrium. O exposure to aim O vacancy elimination is not effective, since O vacancy elimination condition is equivalent to the Si substrate oxidation which leads to the increase in Equivalent oxide thickness (EOT). We also studied the mechanism of FLP induced by the reduction with H₂ anneal. FLP with H₂ anneal is governed by the O vacancy annihilation reaction by reducing SiO₂ interface layer. Based on these considerations, we propose some recipes for obtaining band-edge-work-function metals.     

Structure and properties of Cd x Hg1−x Te-metal contacts

A metal-semiconductor contact is a composite structure consisting of several nanodimensional layers. The contact properties depend strongly on the technique of metal deposition. A metal forms chemical compounds with the components of Cd _x Hg_1?x Te (CMT), thus changing the properties of the surface layer. Mercury is accumulated at the interface with the metal, while tellurium is accumulated on the metal surface. The CMT compounds with metals, heats of their formation, and the Fermi level shifts are reported. The structure and properties of the interfaces between CMT and gold, silver, indium, aluminum, copper, and other metals, as well as the effect of sublayers of other metals and insulators, are described.     

微机控制的光热辐射技术测量金属的热扩散系数

介绍用光热辐射技术测量材料热扩散系数的基本原理和微机控制测量装置，给出了几种常见金属材料热扩散系数的测量结果，并对影响测量结果的因素进行了讨论，实验结果表明，该技术是一种快速测量材料热学性质的有效手段。     

Extensive electrical and thermal characterization of an MCM-Dtechnology

In this paper, it is shown the work carried out on thermal characterization of the main materials employed in the deposited-type multichip module (MCM-D) technology. In this technology, silicon chips are mounted onto a silicon substrate by a flipchip technique. The substrates can be either passive with interconnection lines, Rs, Cs, and Ls or active with complementary metal oxide semiconductor (CMOS) technology cells. The metals used in this technology are aluminum for interconnection purposes, tantalum silicide for making resistors and a multilayer of wettable metal for solder connection. Measurements of sheet resistance and contact resistance versus temperature in the range of -28°C to 100°C of the metals used in the technology are shown. A set of classic test structures such as Kelvin contacts, cross bridge resistors (CBR), and Van der Pauw structures have been used for this purpose as well as a new Kelvin-like structure to test the contact resistance of the Flip Chip connection through the ball. This structure has been proven to be very sensitive allowing the measurement of changes in ball resistance in the range of mΩ. A thermal model of the MCM package has been obtained, taking into account all the thermal resistances added by this kind of package     

微尺度热传导理论及金属薄膜的短脉冲激光加热

概述了微尺度热传导理论的几种模型及其求解方法。以金属薄膜的短脉冲激光加热为例,分析了固体材料在微尺度条件下的热响应特征,主要包括短脉冲激光加热条件下金属薄膜中的热平衡时间、薄膜中热传递的波动性特征和微尺度条件下热传递的尺寸效应;同时讨论了对流热损失对金属薄膜热行为的影响。     

Structural disordering and viedemann-franz relation in melts of some II-IV-V<Subscript>2</Subscript> semiconductors

The thermal and electrical conductivities, as well as the thermoelectric power of the CdSnAs₂, CdGeAs₂, ZnSnAs₂, and ZnGeAs₂ ternary semiconductor compounds, were studied in both solid and liquid states. It was shown that the thermal and electrical conductivities of these compounds increase, while the thermoelectric power decreases in the course of melting to the values characteristic of liquid metals. In contrast to metal melts, the electrical conductivity and the Lorentz numbers calculated from the Viedemann-Franz relation increase with temperature in II-IV-V₂ semiconductor melts. According to the Mott classification, the melts of these compounds are related to group B. Melting of II-IV-V₂ semiconductors causes their metallization.     

Electrical and photoelectric properties of electrochemically fabricated SnO2/Cd0.4Zn0.6S/CdTe solar cells

Solar cells based on SnO₂/Cd_0.4Zn_0.6S/CdTe heterostructures are fabricated by electrochemical deposition, and the dependences of their electrical and photoelectric properties on the thermal annealing conditions are studied. It is shown that thermal annealing reduces the tunnel currents by almost two orders of magnitude. The best conditions of thermal annealing are determined (t = 300°C and τ = 9 min). These conditions provide the highest photosensitivity of the heterostructures under study (I _sc ≈ 21.2 mA/cm², U _oc ≈ 813 mV, and η = 14.7%).     

Vanadium Oxide Thin Films Alloyed with Ti, Zr, Nb, and Mo for Uncooled Infrared Imaging Applications

Microbolometer-grade vanadium oxide (VO _x ) thin films with 1.3 < x < 2.0 were prepared by pulsed direct-current (DC) sputtering using substrate bias in a controlled oxygen and argon environment. These films were systematically alloyed with Ti, Nb, Mo, and Zr using a second gun and radiofrequency (RF) reactive co-sputtering to probe the effects of the transition metals on the film charge transport characteristics. The results reveal that the temperature coefficient of resistance (TCR) and resistivity are unexpectedly similar for alloyed and unalloyed films up to alloy compositions in the ～20 at.% range. Analysis of the film structures for the case of the 17% Nb-alloyed film by glancing-angle x-ray diffraction and transmission electron microscopy shows that the microstructure remains even with the addition of high concentrations of alloy metal, demonstrating the robust character of the VO _x films to maintain favorable electrical transport properties for bolometer applications. Postdeposition thermal annealing of the alloyed VO _x films further reveals improvement of electrical properties compared with unalloyed films, indicating a direction for further improvements in the materials.     

On the thermal properties of Ag2Te and Ag2Se in the region of the phase transition

A setup is developed for measuring the thermal properties of Ag₂Te and Ag₂Se near the main phase transition and in the region of it in high vacuum. The samples are of stoichiometric composition with an excess of Ag, Te, and Se. Differential thermal analysis is performed and the temperature differences across and along the samples are measured by the pulsed light method. Using data on the thermal diffusivity a(T), the temperature dependence of the thermal conductivity K = apc is determined, where p is the density and c is the specific heat. The measurement technique used allows us to establish that the main phase transitions are accompanied by intense heat release. New phase transitions before and after the main structural phase transition with heat absorption are found. According to the DTA data, in the Ag₂Te sample with an excess of Ag (0.25 at.%, cn = 1.2 × 10¹⁹ cm^?3) the phase transition at 365 K is also accompanied by heat absorption. Thus, it is established that all of the phase transitions in Ag₂Te and Ag₂Se are first-order.     

Thermal Cycling, Mechanical Degradation, and the Effective Figure of Merit of a Thermoelectric Module

Thermoelectric modules experience performance reduction and mechanical failure due to thermomechanical stresses induced by thermal cycling. The present study subjects a thermoelectric module to thermal cycling and evaluates the evolution of its thermoelectric performance through measurements of the thermoelectric figure of merit, ZT, and its individual components. The Seebeck coefficient and thermal conductivity are measured using steady-state infrared microscopy, and the electrical conductivity and ZT are evaluated using the Harman technique. These properties are tracked over many cycles until device failure after 45,000 thermal cycles. The mechanical failure of the TE module is analyzed using high-resolution infrared microscopy and scanning electron microscopy. A reduction in electrical conductivity is the primary mechanism of performance reduction and is likely associated with defects observed during cycling. The effective figure of merit is reduced by 20% through 40,000 cycles and drops by 97% at 45,000 cycles. These results quantify the effect of thermal cycling on a commercial TE module and provide insight into the packaging of a complete TE module for reliable operation.     

Anomalous current distributions in power transistors

Current and temperature distributions of multi-emitter power transistors are analysed. The thermal properties, including thermal coupling, are described by a thermal resistance matrix. Anomalous current distributions over the emitter fingers which may lead to second breakdown are shown to be associated with the eigenstates of this matrix. Voltage and current-controlled second breakdown correspond to different eigenstates; the maximum power is inversely proportional to the relevant eigenvalue λ. The presence of emitter (or base) series resistance R gives rise to a thermal breakdown voltage BV_TH∞R/λ below which the device is always stable. The influence of the spacing between emitter fingers and of the quality of the thermal contact between chip and heat sink on the power handling capability is computed. Experimental evidence is presented which suppors the theory.     

Investigation of n-ohmic contact of vertical GaN-based light-emitting diodes on graphite substrate with Ag-In bonding

Vertical light-emitting diodes (VLEDs) were successfully transferred from a GaN-based sapphire substrate to a graphite substrate by using low-temperature and cost-effective Ag-In bonding, followed by the removal of the sapphire substrate using a laser lift-off (LLO) technique. One reason for the high thermal stability of the AgIn bonding compounds is that both the bonding metals and Cr/Au n-ohmic contact metal are capable of surviving annealing temperatures in excess of 600 °C. Therefore, the annealing of n-ohmic contact was performed at temperatures of 400 °C and 500 °C for 1 min in ambient air by using the rapid thermal annealing (RTA) process. The performance of the n-ohmic contact metal in VLEDs on a graphite substrate was investigated in this study. As a result, the final fabricated VLEDs (chip size: 1000 µm×1000 µm) demonstrated excellent performance with an average output power of 538.64 mW and a low operating voltage of 3.21 V at 350 mA, which corresponds to an enhancement of 9.3% in the light output power and a reduction of 1.8% in the forward voltage compared to that without any n-ohmic contact treatment. This points to a high level of thermal stability and cost-effective Ag-In bonding, which is promising for application to VLED fabrication.     

Characterization of Recrystallization and Microstructure Evolution in Lead-Free Solder Joints Using EBSD and 3D-XRD

Development of vulnerable high-angle grain boundaries (and cracks) from low-angle boundaries during thermal cycling by means of continuous recrystallization was examined in fine-pitch ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (wt.%) (SAC305) lead-free solder joints. Electron backscatter diffraction (EBSD) and differential-aperture x-ray microscopy (DAXM or 3D-XRD) were used for surface and subsurface characterization. A large number of subgrain boundaries were observed in the parent orientation using both techniques. However, unlike studies of anisotropic deformation in noncubic metals at much lower homologous temperatures, no streaked diffraction peaks were observed in DAXM Laue patterns within each 1 μm³ voxel after thermal cycling, suggesting that geometrically necessary dislocations (GNDs) are effectively absorbed by the preexisting subgrain boundaries. Storage at room temperature (0.6T _m) prior to DAXM measurement may also facilitate recovery processes to reduce local GND contents. Heterogeneous residual elastic strains were found near the interface between a precipitated Cu₆Sn₅ particle and the Sn grain, as well as near particular subgrain boundaries in the parent orientation. Grain boundary migration associated with recrystallization resulted in regions without internal strains, subgrain boundaries, or orientation gradients. Development of new grain orientations by continuous recrystallization and subsequent primary recrystallization and grain growth occurred in the regions where the cracks developed. Orientation gradients and subgrain structure were observed within newly formed recrystallized grains that could be correlated with slip systems having high Schmid factors.     

Investigation of impact ionization and flicker noise properties in indium aluminum arsenide/indium gallinum arsenide metamorphic high electron mobility transistors with various work function-gate metals

This study investigates the effect of impact ionization using Ir, Pt, Pd, Ti gate metals and the direct correlation between these high work function metals and low frequency noise (LFN) on an In_0.4Al_0.6As/In_0.4Ga_0.6As metamorphic high electron mobility transistor (MHEMT). The effect of impact ionization on DC, RF, and cryogenic LFN is systematically studied and discussed. Gate metals with high work functions are used to suppress the kink effect and gate leakage current. Experimental results suggest that the Ir gate MHEMT exhibits superior thermal stable properties in a strong electrical field at various temperatures, associated with high gain, high current, and excellent low-frequency noise performance.