Resistivity Of Polycrystalline Research Articles

Tailored Polycrystalline Substrate for SmartSiC<sup>TM</sup> Substrates Enabling High Performance Power Devices

Silicon Carbide (SiC) Power Devices have emerged as a breakthrough technology for a wide range of applications in the frame of high-power electronics, notably in the 600 to 3,300V. The last decades have shown a continuous and impressive improvement in both 4H-SiC wafer size and quality. Nevertheless, the availability of such wafers remains a challenge for the SiC power industry. In the last three years, Soitec has successfully adapted the Smart Cut™ technology to Silicon Carbide, resulting in the integration of a thin layer of high quality 4H-SiC on an ultra-low resistivity 3C p-SiC handle wafer. The so-called SmartSiC™ offers a drastic yield improvement for the whole industry thanks to the multiple times re-use of the 4H-SiC donor wafer, as well as an improvement of the device’s electrical performance, especially thanks to the ultra-low resistivity polycrystalline silicon carbide (p-SiC). The latter being specially developed to enhance the new SmartSiC™ substrate capabilities. In this paper, we present the work done by Mersen and Soitec to tailor the p-SiC properties, and thus the SmartSiC™ ones including such material.

Selective Growth and Contact Gap-Fill of Low Resistivity Si via Microwave Plasma-Enhanced CVD.

Low resistivity polycrystalline Si could be selectively grown in the deep (~200 nm) and narrow patterns (~20 nm) of 20 nm pitch design rule DRAM (Dynamic Random Access Memory) by microwave plasma-enhanced chemical vapor deposition (MW-CVD). We were able to achieve the high phosphorus (CVD gap-fill in a large electrical contact area which does is affected by line pitch size) doping concentration (>2.5 × 1021 cm−3) and, thus, a low resistivity by adjusting source gas (SiH4, H2, PH3) decomposition through MW-CVD with a showerhead controlling the decomposition of source gases by using two different gas injection paths. In this study, a selective growth mechanism was applied by using the deposition/etch cyclic process to achieve the bottom–up process in the L-shaped contact, using H2 plasma that simultaneously promoted the deposition and the etch processes. Additionally, the cyclic selective growth technique was set up by controlling the SiH4 flow rate. The bottom-up process resulted in a uniform doping distribution, as well as an excellent filling capacity without seam and center void formation. Thus, low contact resistivity and higher transistor on-current could be achieved at a high and uniform phosphorus (P)-concentration. Compared to the conventional thermal, this method is expected to be a strong candidate for the complicated deep and narrow contact process.

Preparation of polycrystalline CdZnTe thick film Schottky diode for ultraviolet detectors

High resistivity (3 × 109 Ω cm) polycrystalline CdZnTe thick films with thickness of 25 μm–150 μm were grown on SnO2: F-coated glass substrates by close-spaced sublimation method. The properties of polycrystalline CdZnTe films were studied by XRD, SEM and EDS, respectively. A CdZnTe film Schottky diode detector was also fabricated and investigated using current–voltage and capacitance–voltage methods. The photo-current density of the device was about 1508.69 nA/mm2 under light illumination (λ = 260 nm), at an applied negative voltage of 15 V. The results showed that polycrystalline CdZnTe thick film was suitable for application in ultraviolet detectors.

Ultrasonic study on the Jahn–Teller effect near different phase transitions in La1/3Sr2/3MO3 (M=Mn, Fe, Co)

The longitudinal ultrasonic velocity (Vl), magnetization and resistivity of polycrystalline La1/3Sr2/3MO3 (M=Mn, Fe, Co) have been measured between 20 and 300K. Dramatic anomalies in Vl were observed near the temperature of the charge-ordering transition (CO), charge disproportionation transition (CD), and ferromagnetic transition (FM), which are explained by the Jahn–Teller effect originating from the M ions (M=Mn, Fe, Co). However, the detailed form of these anomalies is different, which is strongly depended on the M ion's unique electronic structure. For La1/3Sr2/3MO3 (M=Mn, Fe), the Vl exhibits a valley around the CO transition temperature because of the localization of the Jahn–Teller active ions (Mn3+, Fe4+). And due to the instability of Fe4+, the CD transition occurs in La1/3Sr2/3FeO3, which results in another softening in Vl, while only normal increase is observed in La1/3Sr2/3MnO3. For La1/3Sr2/3CoO3, the local lattice distortion via the Jahn–Teller effect of intermediate spin Co3+ leads to the velocity anomaly in the ferromagnetic metallic state.

Influence of Mn site doping on electrical resistivity of polycrystalline La1-yAyMn1-xBxO3 (A=Ba, Sr; B=Cu, Cr, Co) Manganites

We have the measured electrical resistivity of La1-yBayMn1-xCuxO3 (0.17?y?0.30; 0.04?x?0.10), La1-ySryMn1-xCrxO3 and La1-ySryMn1-xCoxO3 (0.270?y?0.294; 0.02?x?0.10) polycrystalline samples in the 25-325 K temperature range. The increase of Mn site doping concentration leads to an increase of the electrical resistivity of the samples and the appearance of a ?double-peak? structure in the electrical resistivity versus temperature graphs. The first peak represents the insulator-metal transition in vicinity of the paramagnetic-ferromagnetic transition (TC). We have found that the intensity of the second peak increases with an increase of concentration of Mn substituents, due to the hole scattering by the random potential of the Mn site impurities.

Enhanced extrinsic magnetoresistance in [formula omitted] artificial grain boundaries induced by ion implantation

The resistance of polycrystalline divalent-ion-doped LaMnO 3 has been shown to be highly sensitive to low magnetic fields. To enable direct study of the properties of isolated grain boundaries, we developed a new method to form artificial boundaries in manganite thin films. Metal slits about 70 nm in width were printed by 30 KV focused Ga ion beam nanolithography on a 4 μ m La 2 / 3 Sr 1 / 3 MnO 3 bridge, and the materials in these slits were then irradiated by accelerated H 2 + ions. Using this method, magnetoresistance (MR) > 8 % and > 16 % were, respectively, obtained at 150 and at 10 K in a magnetic field of 1 T. This technique is very promising in terms of its simplicity and flexibility of fabrication and has the potential for high-density integration.

Synthesis of low resistive polycrystalline PrBa 2Cu 3O 7

We have studied difference in electrical transport properties of polycrystalline PrBa 2Cu 3O 7 (Pr123) by changes in synthesis conditions. As raw material we used the carbon free 3N-BaO 2 and the tetravalent Pr free 3N-Pr 2O 3. These raw materials are mixed with CuO and reacted in Ar atmosphere with low oxygen concentration. The temperature dependence of resistivity shows almost semiconductive behavior for all the samples. However, when the samples were prefired in Ar atmosphere with 0.2–0.4% oxygen concentration, the absolute value of resistivity at room temperature decreased to the value close to that of YBa 2Cu 3O 7 superconductor. From these results we think that the control of site occupation of Pr atoms is important to give the low resistive Pr123.

Low electrical resistivity polycrystalline SiGe films obtained by vertical LPCVD for MOS devices

In this study, authors present some morphological and electrical characterization of polycrystalline SiGe thin films (poly-SiGe) deposited by vertical LPCVD using SiH 4, GeH 4 and H 2 mixture in different deposition parameters aiming for MOS gate electrodes. The obtained thin films are very uniform and smooth, with small grain size, feasible to deep submicrom fabrication. The SiGe samples presented resistivity values as low as 0.42 mΩ cm, one order of magnitude lower than poly-Si reference samples. CV and IV measurements points this poly-SiGe as a suitable material for MOS gate electrodes.

Low resistivity polycrystalline ZnO:Al thin films prepared by pulsed laser deposition

The preparation of low resistivity polycrystalline Al-doped ZnO (AZO) thin films on glass substrates by a pulsed laser deposition method is described, including a description of conditions necessary to obtain low resistivity on the order of 1×10−4 Ω cm. The resistivity of transparent conducting AZO films obtained was affected by both the target sintering conditions and the deposition conditions. A decrease in carrier concentration associated with a increase in deposition temperature is ascribed to an increase of oxygen content in the films, resulting from enhancement of oxidation on the substrate surface. An increase in Hall mobility associated with increases of either the deposition temperature or film thickness is attributed to imperfections of the ZnO lattice, as evidenced by improvement of the crystallinity such as an increase of crystallite size. It was found that the mobility is also greatly influenced by a combination of ionized impurity scattering and grain boundary scattering or dislocation scattering. In particular, carrier transport, even in AZO films with high mobility above approximately 30 cm2/V s as well as a carrier concentration on the order of 1020–1021 cm−3, was found to be affected by imperfections of the ZnO lattice.

High-bias current–voltage–temperature characteristics of undoped rf magnetron sputter deposited boron carbide (B5C)/p-type crystalline silicon heterojunctions

The high-bias behaviour of the dark forward and reverse current–voltage (I–V) characteristics of an undoped radio frequency (rf) magnetron sputter deposited boron carbide (p-B5C)/p-type crystalline silicon heterojunction has been investigated at different ambient temperatures (130–300 K). The experimental forward current–voltage–temperature (I–V–T) characteristics indicate that the non-ohmic bulk conduction mechanisms operable in the highly resistive polycrystalline B5C counterpart material of this heterojunction largely determine the behaviour of its forward current at high-bias voltages (>0.3 V). The hopping conduction model of Apsley and Hughes for a flat density of localized energy states (Apsley N and Hughes H P 1975 Phil. Mag. 31 1327) can be utilized to elucidate the bias dependence of the measured heterojunction forward current over an extended bias-voltage range (0.4–2.7 V) at temperatures below 260 K. On the other hand, the junction-like conduction processes occurring in the depletion region should limit the high-bias behaviour of the measured heterojunction reverse current. Bardeen's model for a modified Schottky-like barrier at the p-B5C/p+-Si interface can be satisfactorily applied to describe the reverse current–voltage characteristics at bias voltages larger than 0.4 V.

Temperature- and Pressure-Dependent Electrical Resistance of Lead Sulfide

The resistance of polycrystalline lead sulfide was measured at temperatures of up to 500 K and pressures of up to 5 GPa using a purpose-designed experimental setup. The resistance jump across the phase transition was found to strongly depend on temperature. The band gap of the low-pressure phase was evaluated as a function of pressure. The resistance of the high-pressure phase was shown to exhibit semiconducting behavior, and the band gap of this phase was determined.

Processing and Optical Properties of YAG- and Rare-Earth-Aluminum Oxide-composition Glass Fibers

ABSTRACTRare-earth-aluminum oxide-composition glass fibers 5-50 μm in diameter and containing up to 50 mole % rare-earth oxide were drawn from undercooled liquids 550-650 K below the equilibrium melting point. The fibers have tensile strengths of ∼6 GPa, glass transition temperatures of ∼1150 K, and infrared transmission up to ∼5500 nm. The optical properties of erbium-doped fibers containing up to 12.5 mole % Er2O3 were investigated. The 1/e lifetime of the 4I13/2 excited state was 0.8-7 ms, decreasing with increasing Er concentration. Amplified spontaneous emission measurements indicate extremely broadband spectra, up to 135 nm (3-dB width) in 0.5 mole % fibers. Although this result is encouraging, the gain bandwidth, which has not been measured, is likely narrower. Glass fibers were crystallized by heat treatment under tension at temperatures of 1300-1900 K to form flexible, creep resistant polycrystalline monofilaments with tensile strengths up to 2.4 GPa.

Chemical vapor deposition diamond window as vacuum and tritium confinement barrier for fusion application

A pressure resistant polycrystalline chemical vapor deposition (CVD) diamond disk for a microwave window is used for a vacuum and a tritium confinement boundary in fusion applications. A pressure test of a CVD diamond window disk (2.25 mm in thickness and 100 mm in diameter) was carried out. It was demonstrated that the diamond window tolerated 1.0 MPa (10 atm) in the plenum. The displacement of the window center for both the growth and the nucleation side on the unpressurized side is 40±1 and 41±1 μm, respectively, at the pressure of 1.0 MPa, and these values agree well with those calculated. No damage in the disk and the braze, and no vacuum leakage in the assembly was observed. This result demonstrates that the diamond window assembly could tolerate up to 1.45 MPa. It was experimentally proved that the diamond window satisfied the safety requirement of 0.5 MPa resistance for the vacuum and the tritium confinement boundary of an International Thermonuclear Experimental Reactor. The design prospect for the diamond window of the electron cyclotron heating and current drive system is also discussed, based on the stress analysis using the ABAQUS code.

Effects of Y and Zr Dopants on Grain Boundary Structure in Creep Resistant Polycrystalline Alumina

AbstractDopants Y and Zr at 100 ppm levels in high purity, micron grain-size polycrystalline alumina are mainly segregated to the alumina grain boundaries and strongly reduce high temperature creep. Information about this segregation has come from high resolution STEM composition mapping experiments. Information about local structural surroundings of the dopant atoms has come from EXAFS experiments, and information about local bonding of the dopant atoms has come from XANES experiments. Structural models for dopant grain boundary segregation provide a context for these experimental results and for effects of dopant incorporation on grain boundary mediated transport. Recent experimental and theoretical results are discussed in this paper.

Structure for improving the characteristics of high resistivity polycrystalline resistors

A novel polysilicon resistor structure, which employs a thin field oxide layer under the contact to sink the lateral arsenic dose, has been developed to improve the characteristics of conventional high resistivity phosphorus-doped polycrystalline silicon resistors. Improvements in the variation of sheet resistance with draw length, the voltage coefficient of resistance (VCR) and the temperature coefficient of resistance (TCR) have been confirmed by empirical data.

Diffusion Bonding of CMSX-4 to UDIMET 720 Using PVD-Coated Interfaces and HIP

There is an increasing interest in development of manufacturing methods for Dual Property BLISKs, consisting of creep resistant airfoils and fatigue resistant disks bonded together by a durable joint. Optimum heat treatments are, however, very different for creep resistant single crystal CMSX-4 and fatigue resistant polycrystalline Udimet 720 selected in this study, but fortunately the first aging treatment for CMSX-4 (1140°C, 2–6 h, AC) is similar to the partial solution treatment of U 720 HS2 (115°C, 4h, OQ). Based on this, diffusion bonding was performed by HIP at 1120°C and 200 MPa argon pressure for 4 h, followed by cooling to 400°C. Subsequently, a shortened Udimet 720 HS2 two-step aging treatment was adopted by heating to 650°C for 6 h followed by cooling to 400°C, heating to 760°C for 2 h, and finally cooling to R.T. under remaining HIP pressure. Plasma etching followed by thin (80 nm) PVD coating with either nickel or titanium were used to clean and protect the polished surfaces before joining. The selection of coatings was governed by the possibility to reduce oxidized nickel by flushing with hydrogen at 330°C during evacuation of the HIP capsules, and by the large solubility of oxygen in titanium. Hot tensile testing was performed at 750°C on both joined and reference materials subjected to the modified heat treatment. Initially solution treated Udimet 720 and CMSX-4 comprised the reference materials. The testing showed that joints with Ti-PVD coatings were almost as strong as Udimet 720 (although with very limited elongation), while the joints with Ti-PVD coatings were weaker.

Photovoltaic properties of n-CdS/p-Cu 2Te thin film heterojunctions

Cu 2Te is an important material for solar energy conversion. Cu 2Te films (0.5−2.0 microm) prepared by flash evaporation technique onto Corning 7059 glass substrates kept at 523 K were nearly stoichiometric and polycrystalline with a cubic structure ( a = 6.72 A ̊ ). The grain size was of the order of 0.5–0.6 microm. The electrical conductivity was 100–300Ω −1cm −1 and the films exhibited p-type conduction. Hall mobilities of 30−70cm 2V −1s −1 were obtained and the thermoelectric power ranged from 0.16 to 0.60m V K −1. The optical energy gap was 1.08−1.10 eV and the absorption coefficient lies in the range (0.7−7.5) × 10 5 cm −1. These low resistivity polycrystalline p-Cu 2Te films have been used as an absorber layer in the fabrication of p-Cu 2Te/n-CdS (doped with 1.5 at.% In) thin film heterojunction solar cell. The current density-voltage, capacitance-voltage and spectral response of these junctions were studied. The heterojunction was illuminated in the back-wall configuration and an open-circuit voltage of 560mV, a short-circuit current density of 12.2mA cm −2 and an electrical conversion efficiency of 6.0% have been obtained for a 1 cm 2 area cell under a solar input of 70 mW cm −2.

Characteristics of double-heterostructure GaAs/AlGaAs laser diodes on Si substrates by selective-area molecular-beam epitaxy

We report successful fabrication of GaAs/Al0.26Ga0.74As double-heterostructure (DH) laser diodes grown on patterned Si substrates by molecular-beam epitaxy. The patterned substrate consists of exposed Si stripes with widths ranging from 9 to 70 μm and surrounded by 900-Å thick SiN films on both sides. Oxide-defined contact stripe lasers with stripe widths ranging from 3 to 50 μm were fabricated. Reduction in threshold current densities is observed for selective-area grown lasers due to current confinement effect by the high resistivity polycrystalline GaAs/AlGaAs films surrounding each of the lasers. Built-in index guiding is also observed for the 10 μm-wide stripe laser as evident from its longitudinal mode spectrum and far-field patterns.

Influence of interface scattering on the resistance of polycrystalline Au/Pd multilayered thin films

The resistivity of Au/Pd multilayered thin films, obtained with high-vacuum evaporation, with layer periodicities from 2.34 nm to 23.0 nm is studied as a function of temperature between 4.2 and 300 K. Chemical analysis X-ray diffraction, electron diffraction and transmission electron microscopy served to determine the composition and microstructure of the samples. The scattering contribution of the Au/Pd interfaces was estimated by taking into account the resistivity increase resulting from grain-boundary scattering. Two series of films were investigated, one with alternate Au and Pd layers of equal thickness and the other with constant Au layer thickness and increasing Pd layer thickness. In both series the same value for the interface scattering at the Au/Pd interfaces was found. The results were found to agree reasonably with previous results obtained on Au films.

Fluorine-doped tin oxide—selenium heterojunction for photovoltaic conversion

Selenium, being a low-cost material and readily available in high purity form, is attracting interest for solar cell applications. It has been calculated theoretically [1] that selenium-based heterojunction solar cells can have an efficiency as high as 20%. Shaw and Ghosh [2] have reported that cells with efficiency better than 10% can be fabricated with selenium in the form of heterojunctions. The results on CdO-CdSe-Se and SnO2-CdSe-Se heterojunctions [2, 3] indicate a conversion efficiency of the order of 3%. Nakada and Kunioka [4] have developed an indium tin oxide (ITO)-selenium heterojunction solar cell having an efficiency of 3.3%. In this letter we report the results of fluorine-doped tin oxide (FTO)-selenium heterojunctions. Transparent FTO films were prepared on chemically and ultrasonically cleaned glass substrates using the spray pyrolysis technique described earlier [5]. The FTO films so obtained show optical transmittance of 84% for a wavelength of 540 nm with a sheet resistance of 10 f~/D at room temperature. No antireflection coating was done prior to deposition of FTO. High-purity selenium (99.999%) obtained from Nuclear Fuel Complex (India) was thermally deposited from a quartz crucible onto the FTO-coated glass slides kept at room temperature. On some of the samples, an ultrathin tellurium layer (1 to 5 nm) was deposited prior to selenium coating. The selenium film was intentionally grown as amorphous to have better control over thickness and surface morphology. A silver overlayer was grown on the selenium to give electrical contact and back-field reflectance. A conducting silver paste was used to take electrical contacts from the silver film. All the vacuum deposition was done in a Hind high-vacuum (India) coating unit 12A4 at a pressure better than 10 -5 torr using a liquid nitrogen trap. The thickness of the film was measured using an FECO interferometer. The selenium sandwich was subjected to thermal shocks at 200 ° C to convert high resistivity amorphous selenium to low resistivity polycrystalline selenium.