Dependence of photoluminescence and electrical properties with rapid thermal annealing in nitrogen-implanted ZnO films

Undoped (as-grown) ZnO films grown by pulsed laser deposition on Al₂O₃ (0001) substrates were doped with nitrogen by means of an ion implantation process. Post-implantation annealing behavior in the temperature range between 500 and 700 °C has been studied by photoluminescence and Hall effect measurements. The implanted films show no peak other than the excitonic recombination emission in the as-implanted state, however, after rapid thermal annealing at 700 °C they reveal a nitrogen acceptor related emission at 3.273 eV. The as-implanted ZnO films show more electron concentrations than the as-grown, unimplanted ZnO film. In contrast, after annealing, the electron concentration in the implanted films is significantly reduced, indicating that the incorporated nitrogen becomes activated after the thermal annealing, then produces holes and eventually compensates for certain amount of electrons. The results imply that a proper nitrogen implantation and subsequent annealing may be a way to produce p-type ZnO films.     

Two-dimensional pentagon quasicrystal in an Al-Co-Ni-Tb alloy obtained by quenching under high static pressure

A transmission electron microscopy study of quasicrystals was carried out in Al-Co-Ni-Tb alloy which was obtained by quenching under high static pressure and a new two-dimensional pentagonal quasicrystal was discovered. An unique five-fold axis is observed in its diffraction patterns and the periodicity along the five-fold axis is 0.4 nm. Another feature of the pentagonal phase is that no extinction exists in the diffraction patterns along the direction perpendicular to the five-fold axis. A comparison of the high resolution electron microscopy images of the pentagonal phase and the decagonal quasicrystal is given. The effect of high pressure is discussed.     

Formation of microcrystalline silicon films using rapid crystal aluminum induced crystallization under low-temperature rapid thermal annealing

The process of obtaining thin film solar cells using the method of aluminum-induced crystallization under rapid thermal annealing (RTA) was investigated. 200-nm-thick amorphous Si (a-Si) film was deposited on a glass substrate using an ultra-high vacuum ion beam sputtering system. A 50-nm-thick crystal aluminum layer was then evaporated and deposited onto the a-Si film. In contrast to conventional furnace annealing, RTA can supply rapid thermal energy so that a-Si can be induced into microcrystalline-Si (μc-Si) in a short time at low temperatures. The crystal Al may promote the crystallization reaction because its surface energy is higher than 0.89 N/m, which is the minimum energy required to produce the (111) orientation. Free Si atoms are induced at the interface of the Al and Si sub-layers by the diffusion of Al along the grain boundaries. The Raman spectrum shows that the sample could be induced to crystallize at 350 °C. After the aluminum was etched, the maximum grain size was 4 μm. The carrier mobility was between 6.2 cm²/Vs and 18.8 cm²/Vs. The proposed method can be used to obtain μc-Si with reduced energy and time during the thermal annealing.     

Formation of non-equilibrium alloys by high pressure melt quenching

Melt quenching under high pressure can promote the formation of metastable materials. High pressure accelerates the amorphization of Cu₆₀Ti₄₀ and Cd₄₃Sb₅₇. For an alloy systems having volume expansion after solidification, the higher the applied pressure, the lower the melting point and the higher the amorphization temperature, which promotes the formation of metallic glass. High pressure also enhances nucleation and suppresses grain growth, so solidification under high pressure can refine the crystal grains to form nanocrystalline alloys, such as Ti₆₀Cu₄₀, Cu₇₀Si₃₀ and Pd₇₈Si₁₆Cu₆ alloys.     

Fe-Si-B amorphous alloys with high silicon concentration

Amorphous phase formation with good ductility has been found in Fe-Si-B ternary alloys with high silicon concentration using a melt-spinning technique. The formation range of these amorphous alloys is in the range 0 to 29 at % silicon and 5 to 26 at % boron, being much wider than the previously reported range (0 to 19 at % silicon and 10 to 26 at % boron). The crystallization temperature (T _x) and Vickers hardness (H _v) of the Fe-Si-B amorphous alloys containing more than 19 at % silicon increase significantly with increasing boron content, while the increase in silicon content causes a decrease inT _x andH _v. TheT _x andH _v of Fe₆₆Si₂₈B₆ alloy with the highest silicon concentration are 740 K and 500 DPN, respectively. The decreases inT _x andH _v with silicon content are interpreted owing to the increase in the contribution of the repulsive interaction between silicon and silicon against the attractive interactions between iron and silicon or boron. Furthermore, the silicon-rich amorphous phase has been found to crystallize by the almost simultaneous precipitation of the two equilibrium compounds of Fe₃Si and Fe₂B, Fe₂Si_0.4B_0.6 or Fe_4.9Si₂B.     

Microstructure and mechanical properties of novel Al-Y-Sc alloys with high thermal stability and electrical conductivity

The microstructure and mechanical properties of novel Al-Y-Sc alloys with high thermal stability and electrical conductivity were investigated.Eutectic Al3 Y-phase particles of size 100-200 nm were detected in the as-cast microstructure of the alloys.Al3 Y-phase particles provided a higher hardness to as cast alloys than homogenized alloys in the temperature range of 370-440℃.L12 precipitates of the Al3(ScxYy) phase were nucleated homogenously within the aluminium matrix and heterogeneously on the dislocations during annealing at 400℃.The average size of the L12 precipitates was 11±2 nm after annealing for 1 h,and 25-30 nm after annealing for 5 h,which led to a decrease in the hardness of the Al-0.2 Y-0.2 Sc alloy to15 HV.The recrystallization temperature exceeded 350℃and 450℃for the Al-0.2 Y-0.05 Sc and Al-0.2 Y-0.2 Sc alloys,respectively.The investigated alloys demonstrated good thermal stability of the hardness and tensile properties after annealing the rolled alloys at 200 and 300℃,due to fixing of the dislocations and grain boundaries by L12 precipitates and eutectic Al3 Y-phase particles.The good combination of strength,plasticity,and electrical conductivity of the investigated Al-0.2 Y-0.2 Sc alloys make it a promising candidate for electrical conductors.The alloys exhibited a yield stress of 177-183 MPa,ultimate tensile stress of 199-202 MPa,elongation of 15.2-15.8%,and electrical conductivity of 60.8%-61.5% IACS.     

The electrical properties of silicon monoxide

Measurements are reported of the d.c. and a.c. properties of two samples of evaporated silicon monoxide sandwiched between aluminium electrodes. The two samples have d.c. conductivities in the ratio 10³:1, while the a.c. conductivities are in the ratio 3:1. The high field behaviour is attributable to the Poole-Frenkel mechanism. The a.c. conductivity show the familiar frequency dependence σ′∝ωⁿ with n≈0.6 for both samples in the lower frequency range. The more conducting sample shows evidence of a second loss mechanism with n≈0.9 at higher frequencies. Good consistency with Kramers-Kronig relations is obtained and the conclusion is drawn that the a.c. mechanism is such that the real and the imaginary components of the complex dielectric susceptibility are proportional to one another regardless of frequency, both obeying the relation χ′∝χ″∝ω^n?1. It is found that the d.c. and a.c. activation energies are equal within the accuracy of the measurements.     

Surfaces with high solar reflectance and high thermal emittance on structured silicon for spacecraft thermal control

Presented here is an examination of unstructured and structured (by anisotropic etching), monocrystalline silicon wafers coated with sputter deposited aluminum and chemical vapor deposited silicon dioxide for high solar reflectance and high thermal emittance, respectively. The topography of the samples was characterized with optical and scanning electron microscopy. Optical properties were examined with reflectance and transmittance spectroscopy, partly by usage of an integrating sphere. The measurement results were used to estimate the equilibrium temperature of the surfaces in space. The suitability of the surfaces with high solar reflectance and high thermal emittance to aid in the thermal control of miniaturized, highly integrated components for space applications is discussed. A silicon dioxide layer on a metal layer results in a slightly lower reflectance when compared to surfaces with only a metal layer, but might be beneficial for miniaturized space components and modules that have to dissipate internally generated heat into open space. Additionally, it is an advantage to microstructure the emitting surface for enhanced radiation of excess heat.     

Effects of rapid thermal treatments on Ti/TiN/Si structures for electrical contacts on silicon

Abstract

A possible new technique for metallisations in Si microelectronics technology has been prepared and characterised. Bilayers of TiN_x/Ti were deposited by sputtering over a Si substrate. The samples were annealed in a rapid thermal processing system, and further analysed using Auger electron spectroscopy and electrical measurements (Schottky barrier height and sheet resistance). Significant differences from the more usual silicidiltion process of a Ti/Si structure have been observed. The silicidation process of the TiN_x/Ti structures is mainly controlled by the presence of the intermediate TiN layer. The final structure was determined to be Si/TiSi_x/TiN_y/TiSi_z.

MST/3336     

Boron induced recrystallization of amorphous silicon film by a rapid thermal process

Rapid thermal process (RTP) is to induce boron-doped amorphous silicon into a high degree of crystallization of polycrystalline silicon in 5 min. In addition to the short time characteristic, it also provides a relatively lower temperature route to prepare high percentage of polycrystalline silicon in comparison with solid phase crystallization method. Before RTP, boron is homogeneously doped into the amorphous silicon film by ion implantation technology. After rapid thermal processing, the grain size of the polycrystalline silicon was found about at 0.1-0.5 μm. The degree crystallization of silicon is reached up to 99.1% with a good hole mobility of 138.6 cm²/V s.     

Effects of rapid thermal annealing on the morphology and electrical properties of ZnO/In films

Zinc oxide (ZnO) films were prepared by ultrasonic spray pyrolysis on indium (In) films deposited by evaporation and subsequently subjected to rapid thermal annealing (RTA) in air or vacuum. The crystallographic properties and surface morphology of the films were characterized before and after RTA by X-ray diffraction and scanning electron microscopy, respectively. The variation in resistivity of the films with RTA temperature and time was measured by the four-point probe method. Auger electron spectroscopy (AES) was carried out to determine the distribution of indium atoms in the ZnO films. The resistivity of the ZnO on In (ZnO/In) films decreased to 2×10⁻³ Ω cm by diffusion of the In. Indium diffusion into the ZnO films roughened the film surface. The results of depth profiling by AES showed a hump of In atoms around ZnO/In interface after RTA at 800 °C, which disappeared on RTA at 1000 °C. The effects of temperature, time and atmosphere during RTA on the structural and electrical properties of the ZnO/In films are discussed.     

Preparation of a new Al-Cu-Fe quasicrystal with large grain sizes by rapid solidification

Journal of Materials Science Letters -     

Characterization of microstructure,texture and magnetic properties in twin-roll casting high silicon non-oriented electrical steel

An Fe-6.5 wt.% Si-0.3 wt.% Al as-cast sheet was produced by twin-roll strip casting process, then treated with hot rolling, warm rolling and annealing. A detailed study of the microstructure and texture evolution at different processing stages was carried out by optical microscopy, X-ray diffraction and electron backscattered diffraction analysis. The initial as-cast strip showed strong columnar grains and pronounced < 001 >//ND texture. The hot rolled & warm rolled sheets were characterized by large amounts of shear bands distributed through the thickness together with strong < 110 >//RD texture and weak < 111 >//ND texture. After annealing, detrimental < 111 >//ND texture almost disappeared while beneficial {001}<210 >, {001}<010 >, {115}<5 − 10 1 > and {410} < 001 > recrystallization textures were formed, thus the magnetic induction of the annealed sheet was significantly improved. The recrystallization texture in the present study could be explained by preferred nucleation and grain growth mechanism.     

High-performance flat-panel solar thermoelectric generators with high thermal concentration

The conversion of sunlight into electricity has been dominated by photovoltaic and solar thermal power generation. Photovoltaic cells are deployed widely, mostly as flat panels, whereas solar thermal electricity generation relying on optical concentrators and mechanical heat engines is only seen in large-scale power plants. Here we demonstrate a promising flat-panel solar thermal to electric power conversion technology based on the Seebeck effect and high thermal concentration, thus enabling wider applications. The developed solar thermoelectric generators (STEGs) achieved a peak efficiency of 4.6% under AM1.5G (1 kW m(-2)) conditions. The efficiency is 7-8 times higher than the previously reported best value for a flat-panel STEG, and is enabled by the use of high-performance nanostructured thermoelectric materials and spectrally-selective solar absorbers in an innovative design that exploits high thermal concentration in an evacuated environment. Our work opens up a promising new approach which has the potential to achieve cost-effective conversion of solar energy into electricity.     

Optical properties and hydrogen concentration in amorphous silicon

We have made a systematic study of the dependence of hydrogen concentration and optical properties on the deposition parameters for amorphous silicon prepared by r.f. glow discharge decomposition of silane. The hydrogen content and the optical gap decrease with increasing deposition temperature T_s, but we also found that the application of an electrical bias to the substrate results in a large increase of the hydrogen content.The rate of increase of the optical gap with the hydrogen content varies with the deposition conditions. This is interpreted as the result of different modes of incorporation of the hydrogen in the material.     

IR and electrical properties of thin silicon oxynitride films synthesized by ion implantation

Silicon oxynitride (Si_xO_yN_z) layers were synthesized by implanting single-crystal silicon with ¹⁴N₂⁺ and ¹⁶O₂⁺ 30 keV ions in different proportions to doses varying from 1 × 10¹⁷ to 1 × 10¹⁸ ions cm^-2. IR transmission techniques were used to investigate the structural dependence on the total ion dose and on the annealing temperature. Electrical properties, namely the dielectric strength and the current-voltage and capacitance-voltage characteristics, of the ion-beam-synthesized Si_xO_yN_z layers and changes in them after annealing were measured.