Properties of amorphous carbon layers for bio-tribological applications

This paper analyses the influence of composition, structure and adhesion of amorphous coatings with high wear resistance, low friction coefficient and good adhesion to coated CrCoMo material for parts of implants. By different deposition techniques, different mechanical and tribological properties were obtained. This work reviews amorphous carbon (a-C) films deposited by magnetron sputtering and diamond-like carbon (DLC) films grown by glow arc discharge technology on CrCoMo substrates. Films were investigated under static load under dry conditions (nanohardness, elastic module), and also with dynamic load (coefficient of friction, wear resistance). The following topics were investigated: surfaces and subsurface properties of a-C films, namely adhesion in connection with different techniques, different film properties in dependence on various technology conditions.     

A novel coplanar amorphous silicon thin-film transistor usingsilicide layers

A novel, coplanar, hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) was fabricated by depositing a triple layer consisting of a-Si:H, silicon-nitride, and a-Si:H. After patterning the top two layers in the gate stack, the devices were doped and a 30 nm Ni layer was deposited. The devices were then annealed for 1 h at 230°C to form self-aligned, low resistive Ni-silicide. The fabricated coplanar a-Si:H TFT exhibits a field effect mobility of 0.6 cm²/Vs, a threshold voltage of 2 V, a subthreshold slope of 0.4 V/dec, and an on/off current ratio of ~10⁷     

Ultralow-frequency photoelectric response of amorphous As2Se3 layers

The results of studying the photodielectric effect in amorphous layers of As₂Se₃ are reported. Agreement between the experimental and theoretical functions of the relative variation in the conductivity in the infralow-frequency region is observed. The dispersion of the recombination coefficient exhibits a minimum. Possible causes of the observed dependences are discussed.     

Redistribution of erbium during the crystallization of buried amorphous silicon layers

The redistribution of Er during its implantation in silicon at doses close to the amorphization threshold and its subsequent solid-phase epitaxial (SPE) crystallization is investigated. The formation of a buried amorphous (a) layer is discovered at Er doses equal to 5×10¹³ and 1×10¹⁴ cm⁻² using Rutherford backscattering. The segregation of Er in this case takes place inwardly from the two directions corresponding to the upper and lower boundaries of the buried αlayer and leads to the formation of a concentration peak at the meeting place of the two crystallization fronts. A method for calculating the coordinate dependence of the segregation coefficient k from the distribution profiles of the erbium impurity before and after annealing is proposed. The k(x) curve exhibits a drop, whose width increases with decreasing Er implantation dose. Its appearance is attributed to the nonequilibrium nature of the segregation process at the beginning of SPE crystallization. Fiz. Tekh. Poluprovodn. 33, 652–655 (June 1999)     

Regrowth of amorphous layers in silicon-on-insulator structures formed by the implantation of oxygen

Synthesised silicon-on-insulator structures have been formed and implanted with 1×1016 As+ cm?2 at 40 keV. The regrowth kinetics of the amorphised layer, which also contains lattice defects and excess oxygen, has been studied by Rutherford backscattering. The regrowth of the layer occurs at a mean rate of 13 ? min?1 at 500°C with an activation energy of 2.7±0.2 eV. This experiment further demonstrates the suitability of these synthesised structures as a direct replacement for bulk silicon in VLSI technology.     

n-i-p型非晶硅太阳电池中p/ITO界面特性研究

采用射频等离子体增强化学气相沉积(RF-PECVD)技术,制备n-i-p型非晶硅(a-Si)太阳电池,采用反应热蒸发法制备ITO薄膜作为太阳电池的前电极。通过改变B2H6的掺杂浓度获得了不同晶化率的p层,详细研究了p层性能对p/ITO界面特性以及电池性能的影响。结果表明,在合适晶化率的p层上沉积ITO薄膜有利于优化p/ITO界面的接触特性,将其应用于n-i-p型a-Si太阳电池,能够显著改善电池的开路电压(Voc)和填充因子(FF),最终,在不锈钢(SS)衬底上获得了转换效率为6.57%的单结a-Si太阳电池。     

Magnetic properties of iron-modified amorphous carbon

The structure and magnetic properties of films of iron-modified amorphous carbon (a-C:Fe) prepared by magnetron cosputtering of iron and graphite targets are studied. X-ray diffraction measurements show that iron enters the samples in the form of Fe nanocrystals that are typically about 20 nm in size and also forms nanocrystals of hexagonal iron carbide. The temperature dependences of the magnetization, measured under cooling in zero and nonzero magnetic fields, are studied. At temperatures T ? 8 K, a magnetic transition, which provides evidence for the onset of magnetic ordering in the material, is observed to occur. The magnetization isotherms obtained in the 8-to 20-K temperature range are in agreement with this observation. It is shown that a modified version of Langevin’s formalism adequately describes the observed features of a-C:Fe film magnetization.     

In situ study of the formation of silicide phases in amorphous Co-Si mixed layers

We investigate Co silicide phase formation when extra Si is added within an as deposited 50 nm Co film. The addition of Si is investigated for both the Co/SiO₂ and Co/Si(1 0 0) system. A series of 10 Co-Si mixed films with a Si content varying from 21 to 59 at.% was prepared and investigated during annealing with in situ X-ray diffraction. The oxide system is used as reference system to identify phases that initially crystallize in an amorphous mixture of a given composition. Multiple phases can nucleate, and the temperature of crystallization depends on the Co-Si atomic ratio. Upon heating of the Co(Si)/Si system, the first reaction is a similar crystallization reaction of the Co(Si) mixture. Once the first phase is formed, one has the normal system of a silicide phase in contact with an unlimited amount of Si from the substrate, and the sequential phase formation towards CoSi₂ is established. For deposited layers of composition ranging from 48%Si to 52%Si, the CoSi is the first phase to form and increasing the amount of Si leads to a remarkable improvement of the thermal stability of CoSi on Si(1 0 0). CoSi₂ nucleation was extensively delayed by 150 °C compared to the reaction observed from a pure Co film on Si(1 0 0). Electron backscatter diffraction measurements reveal that in this range, the gradual Si increase systematically leads to bigger CoSi grains (up to 20 μm). This shows that the grain size of the CoSi precursor strongly affects the nucleation of the following CoSi₂ phase. Laser-light scattering measurements suggest that adding more than 42%Si reduces the roughness of the CoSi₂ layer.     

Interfacial reactions in the pb-free composite solders with indium layers

A Pb-free composite solder is prepared with a Pb-free solder substrate and a plated-indium layer. The indium layer melts during the soldering process, wets the substrates, and forms a sound solder joint. Since the melting temperature of indium is 156.6°C, lower than that of the eutectic Sn-Pb, which is at 183°C, the soldering process can be carried out at a temperature lower than that of the conventional soldering process. Composite solder joints with three different Pb-free solders, Sn, Sn-3.5 wt.% Ag, and Sn-3.5 wt.% Ag-0.5 wt.% Cu, and two substrates, Ni and Cu, are prepared. The interfaces between the indium layer, Pb-free solder, and Ni and Cu substrate are examined. A good solder joint is formed after a 2-min reflow at 170°C. A very thick reaction zone at the indium/Pb-free solder interface and a thin reaction layer at the indium/substrate interface are observed.     

Device characteristics of amorphous indium-gallium-zinc-oxide channel capped with silicon oxide passivation layers

It was investigated how the amorphous indium-gallium-zinc-oxide (a-IGZO) channel of a back-gate of thin film transistor (TFT) is affected by the deposition of silicon oxide layers on their top surfaces by radio frequency magnetron sputtering. Preliminary investigations showed that the deposition of silicon oxide layer caused damages to the surfaces of pristine silicon wafers resulting in substantial roughening. However, bombardments by the energetic particles involved in the sputtering process seem to have played beneficial roles in that the a-IGZO channel TFTs showed improved performances in respect of the carrier density, field effect mobility, and on-off current ratio. Such improvements are attributed to the modification of the a-IGZO channel to decrease the concentration of oxygen vacancy sites and/or to average the oxygen vacancy sites thereby increasing the carrier concentrations and decreasing the density of trap sites, as revealed in the negative shift of the threshold voltage. On the other hand, such channel modification by the passivation process resulted in the slight increase in the subthreshold swing. It is suggested that the a-IGZO channel TFTs can be passivated by simple sputtering process without etch stop layer since the process rather improved the device performances despite some damages to the passivated surfaces.     

Sputtered oxides used for passivation layers of amorphous InGaZnO thin film transistors

Four sputtered oxide films (SiO₂, Al₂O₃, Y₂O₃ and TiO₂) along with their passivating amorphous InGaZnO thin film transistors (a-IGZO TFTs) were comparatively studied in this paper. The device passivated by an Al₂O₃ thin film showed both satisfactory performance (μ_FE=5.3 cm²/V s, I_on/I_off>10⁷) and stability, as was probably related to smooth surface of Al₂O₃ thin films. Although the performance of the a-IGZO TFTs with a TiO₂ passivation layer was also good enough (μ_FE=3.5 cm²/V s, I_on/I_off>10⁷), apparent V_th shift occurred in positive bias-stress tests due to the abnormal interface state between IGZO and TiO₂ thin films. Sputtered Y₂O₃ was proved no potential for passivation layers of a-IGZO TFTs in this study. Despite unsatisfactory performance of the corresponding a-IGZO TFT devices, sputtered SiO₂ passivation layer might still be preferred for its high deposition rate and excellent transparency which benefit the mass production of flat panel displays, especially active-matrix liquid crystal displays.     

Characterization of crystalline low temperature GaAs layers annealed from an amorphous phase

The results from an in-depth characterization of as-grown and annealed low-temperature GaAs layers deposited at less than 260°C are presented. The layers, amorphous as grown, became crystalline after annealing. The crystallization was documented by several characterization techniques including photoreflectance, Raman spectroscopy, photoluminescence, transmission electron microscopy, and double-crystal x-ray diffraction. The n-type conductivity of the annealed films was exploited for the construction of a diode structure.     

Phase transformations initiated in thin layers of amorphous silicon by nanosecond excimer laser pulses

The reflection of a probing beam with a wavelength λ=0.63 μm from a silicon surface layer (a-Si) amorphized by ion implantation was detected during its melting and solidification initiated by excimer ArF laser radiation. When the irradiation energy is below the epitaxial threshold, a single event of a-Si layer melting leads to the formation of single nanocrystals separated from one another in the amorphous matrix rather than to the appearance of polycrystalline material. The presence of nanocrystals makes possible the formation of polycrystalline Si from a melt under exposure to a second laser pulse and allows the intermediate crystallization of Si in a laser-induced sequence of phase transitions. The data obtained are compared to the results of studying the phase transitions initiated in similar experimental conditions in thin layers of hydrogenated a-Si layers on glass substrates. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 5, 2003, pp. 622–628. Original Russian Text Copyright ? 2003 by Ivlev, Gatskevich.     

Improved photovoltaic properties of amorphous silicon thin-film solar cells with an un-doped silicon oxide layer

This paper proposes the use of undoped hydrogenated microcrystalline silicon oxide (μc-SiO_x:H) deposited on the n-μc-Si:H layer of amorphous silicon single-junction superstrate configuration thin-film solar cells produced through 40 MHz very high frequency plasma-enhanced chemical vapor deposition. Raman spectroscopy and optoelectronic analyses of the undoped μc-SiO_x:H thin film revealed that adding a small amount of oxygen into a μc-network results in a low optical absorption, wide band gap, high optical band gap E₀₄, high refractive index, reasonable conductivity, and crystalline volume fraction, which are advantageous properties in solar cells. Compared with a standard cell, the current density–voltage (J–V) characteristics of the cell with an undoped μc-SiO_x:H/n-μc-Si:H structure showed an enhancement in short-circuit current density J_sc from 13.32 to 13.60 mA/cm², and in conversion efficiency from 8.53% to 8.61%. The increased J_sc mechanism can be attributed to an improved light-trapping capability in the long wavelength range between 510 and 660 nm, as demonstrated by the external quantum efficiency.     

Collection efficiency in amorphous silicon solar cells

A simple relation is presented for the field assisted collection efficiency for amorphous silicon solar cells, assuming zero geminate recombination. The ratio of the collection efficiency under forward biasing condition to short circuited condition is computed. It is found to agree reasonably well with the experimentally observed values.     

PI衬底柔性透明硅薄膜太阳能电池的制备及性能

利用硬质玻璃为载板,采用传统硅薄膜太阳能电池生产设备,在聚酰亚胺(PI)塑料薄膜衬底上沉积了B掺杂的ZnO(BZO)薄膜,并以此作为前电极制备了单节电池结构及多节串联一体结构的非晶硅(a-Si)太阳能电池;研究了PI衬底上BZO薄膜的光学及电学性能。结果表明,PI衬底上沉积BZO薄膜后在300~1 200 nm波长范围的透光率为76.63%,方块电阻19.7?/□。所制备的单节和多节串联一体结构的a-Si薄膜太阳能电池的转化效率分别达到6.45%和5.1%,封装后电池组件具有一定的透光性,透光率约达到30.2%。     

Electronic properties of amorphous silicon in solar cell operation

Amorphous silicon (a-Si) solar cells, which have efficiencies up to 5.5 percent, are unique in several ways, and their cell characteristics no longer depend on the same parameters generally considered in single crystal cells. This paper discusses the operation of such cells, and relates the major new parameters to the electronic properties of a-Si which are highly dependent on the densities of gap centers in this disordered material. The effect of the photoconductivity in intrinsic a-Si on the series resistance of the cell, the quality of a-Si junctions and their ability to transport current densities generated under AM1 illumination are presented. Space-charge densities as low as 5 × 10¹⁵cm^-3are found in a-Si junctions, which are orders of magnitude lower than previous estimates for glow discharge produced a-Si. The effects of electric field distributions and diffusion lengths of holes on collection efficiencies and cell characteristics are discussed and illustrated. Although significant trapping of photogenerated holes is found in many of the a-Si films, diffusion lengths of few tenths of a micron are also indicated by the results presented.     

Low temperature fuel cells

Fuel cells have emerged from the research laboratories and are now in the state of being actively developed for various military and commercial purposes. The paper tries to describe the principal problems which had to be overcome to build reliably operating, relatively inexpensive cells. The different systems presently used are compared with each other and the possibility of the use of cheap hydrocarbon fuels in low temperature cells is discussed.     

Application of sputter-deposited amorphous and anatase TiO2 as electron-collecting layers in inverted organic photovoltaics

We demonstrate the deposition of amorphous and anatase TiO₂ on indium tin oxide (ITO) substrates via the process of sputtering, and the use of these materials as electron-collecting layers (ECLs) in inverted-type organic photovoltaics (OPVs). Anatase TiO₂ was obtained via vacuum-annealing of as-deposited amorphous TiO₂ at 300 °C. No deterioration of optical and electrical properties of ITO was observed after both sputter-deposition of TiO₂ and annealing process. The anatase TiO₂ proved to be an effective ECL when employed in inverted OPVs using bulk heterojunction photoactive layer of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester, achieving a power conversion efficiency of 3.3% (J_SC = 9.0 mA cm^?2, V_OC = 0.62 V and FF = 0.60).