Photovoltaic properties of multi-walled carbon nanotubes deposited on n-doped silicon

Multi-wall carbon nanotubes (MWCNTs), grown by catalytic chemical vapor deposition (CCVD) over Fe supported on alumina catalyst, using isobutane as feedstock, are dispersed in aqueous solutions of sodium dodecyl sulfate. Stable and highly photosensitive heterojunctions are developed by liquid-phase deposition of MWCNTs/surfactant mixtures on the top of n-doped monocrystalline silicon wafers. Electrical measurements performed in the dark and under broad-band visible light, show that the hybrid solar cells, despite their non-optimized design, have conversion energy efficiency of the order of 3%.     

SOI／SIMOX材料导电类型反型的研究

采用大剂量氧离子注入（１７０ｋｅＶ，１．８×１０１８＋／ｃｍ２）ｐ型单晶硅，高温退火（１３００℃，６ｈ）后形成ＳＯＩ－ＳＩＭＯＸ（ＳｉｌｉｃｏｎＯｎＩｎｓｕｌａｔｏｒ－ＳｅｐａｒａｔｉｏｎｂｙＩｍｐｌａｎｔａｔｌｏｎｏｆＯｘｙｇｅｎ）样品。俄歇电子能谱仪和扩展电阻仪测试表明，该样品表层硅膜的导电类型由ｐ型反型为ｎ型。ＳＩＭＯＸ样品的反型是硅中的氧施主所致，由近自由电子的类氦模型计算，ＳＩＭＯＸ样品中氧施主的电离能为０．１５ｅＶ，与早期文献报导的实验值一致。     

C-V and C-t analysis of buried oxide layers formed by high-dose oxygen implantation

For silicon-on-insulator devices with very thin active layers, the quality of the buried oxide layer and its interface with the top silicon layer can significantly affect device performance. This study focuses on the characterization of buried oxide layers formed by high-dose oxygen implantation into Si wafers. Capacitance-voltage (C-V) and capac-itance-time (C-t) measurements were performed on the epilayer/buried oxide/substrate capacitors. From high frequency C-V measurements, data on fixed oxide charge, inter-face traps, and donor densities were obtained for both buried oxide interfaces, as well as the thickness of the buried oxide layer. From C-t measurements, minority carrier generation lifetimes were calculated for thin depletion regions on both sides of the buried oxide. The data is correlated to changes in implanted dose, anneal temperature, and anneal time.     

Modification of the properties of porous silicon on adsorption of iodine molecules

Infrared spectroscopy and electron spin resonance measurements are used to study the properties of porous silicon layers on adsorption of the I₂ iodine molecules. The layers are formed on the p-an n-Si single-crystal wafers. It is established that, in the atmosphere of I₂ molecules, the charge-carrier concentration in the layers produced on the p-type wafers can be noticeably increased: the concentration of holes can attain values on the order of ～10¹⁸?10¹⁹ cm^?3. In porous silicon layers formed on the n-type wafers, the adsorption-induced inversion of the type of charge carriers and the partial substitution of silicon-hydrogen bonds by silicon-iodine bonds are observed. A decrease in the concentration of surface paramagnetic defects, P _b centers, is observed in the samples with adsorbed iodine. The experimental data are interpreted in the context of the model in which it is assumed that both deep and shallow acceptor states are formed at the surface of silicon nanocrystals upon the adsorption of I₂ molecules.     

多线切割加工中单晶硅片晶向影响关系研究

单晶硅片的晶向是大规模集成电路衬底材料的一个重要参数。硅片的晶向是根据单晶的生长晶向以一定的角度粘结固定到多线切割机的工作台上切割实现的。但是在实际粘结操作过程中,单晶棒易滑移导致角度产生偏差从而影响到加工后的硅片晶向超差而报废。为了明确粘结角度偏差对切割后硅片晶向的影响关系,在产生误差的情况下做出科学正确的判断,对粘结角度的计算原理进行了推导、得出了单晶棒X．ray定向仪的计算原理。在此基础上,对粘结产生的角度误差对晶向的影响关系进行了理论推导．得出了它们之间的明确影响关系的函数关系。此函数关系表明。粘结过程的角度误差对硅片晶向的影响是复杂的反三角函数关系,必须通过实际计算才能确定其大小。通过此函数关系,可以明确的确定单晶棒粘结的角度偏差对硅片晶向的影响。为科学的现场判断提供了理论依据,能有效的服务于生产实际,．     

Phosphorus gettering of iron by screen‐printed emitters in monocrystalline Czochralski silicon wafers

In this paper, we demonstrate single‐sided screen‐printed emitters in thin monocrystalline Czochralski silicon (Cz‐Si) wafers with an improved gettering of iron compared with conventional double‐sided POCl₃ emitters. The phosphorus dopant pastes used have to be chosen carefully to provide a sufficiently low emitter sheet resistance and to avoid iron contamination. The iron concentration is determined in a non‐destructive way from the minority carrier lifetime obtained by quasi‐steady‐state photoconductance measurements, down to levels not yet demonstrated for screen‐printed emitters. In addition, the well‐known metastable boron–oxygen complexes in Cz‐Si have been transferred into a stable state by light‐induced degradation prior to these measurements. Copyright © 2012 John Wiley & Sons, Ltd.     

Fabrication and electrical characterization of n-InSb on porous Si heterojunctions prepared by liquid phase epitaxy

Thin films of InSb were grown on p-type porous silicon (PSi) (1 1 1) substrates by liquid phase epitaxy (LPE) to obtain monocrystalline InSb epilayer on a PSi substrate for low cost device applications. The structural characterization of the devices was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The X-ray diffraction measurements indicate that InSb monocrystalline epilayer was successfully grown onto PSi. The current-voltage (I-V) characteristics of n-InSb/p-PSi heterojunction devices were measured in the temperature range of 298-398 K. The measurements indicate that these heterojunctions have good rectifying characteristics. The estimated zero-bias barrier height φ_BO and the ideality factor η show strong temperature dependence. The conventional Richardson plot exhibits linear behavior in the entire temperature range indicating that the conduction seems to be predominantly due to thermionic emission mechanism. In addition, the capacitance-voltage characteristics are investigated at frequency of 1 MHz. The built-in potential of the heterojunction is determined after eliminating the effect of the capacitance effect of the interface state caused by the lattice mismatch.     

Electrochemical polishing of monocrystalline silicon with specific crystallographic planes

In this study, an electrolytic polishing experimental system was developed to obtain a uniform, flat-surfaced monocrystalline silicon with specific crystallographic planes. Several key factors reflecting specific electrolytic polishing on monocrystalline silicon with specific crystallographic planes were summarized. These factors, including electrolyte, conduction mode, Schottky barrier, semiconductor body resistance, and unidirectional conductivity, were analyzed comprehensively through energy spectrum analysis, theoretical modeling, and potential simulation. The effects of electrolytic polishing process were obtained, and corresponding solutions were proposed. Finally, the electrolytic polishing experiment for monocrystalline silicon with specific crystallographic planes was conducted. A uniform, flat-surfaced monocrystalline silicon with no metamorphic layer was then obtained. The flatness error of the center area was less than 0.201 µm. Furthermore, the crystallographic planes of monocrystalline silicon wafers showed no change.     

On the mechanical strength of monocrystalline,multicrystalline and quasi‐monocrystalline silicon wafers: a four‐line bending test study

Quasi‐monocrystalline silicon wafers have appeared as a critical innovation in the PV industry, joining the most favorable characteristics of the conventional substrates: the higher solar cell efficiencies of monocrystalline Czochralski‐Si (Cz‐Si) wafers and the lower cost and the full square‐shape of the multicrystalline ones. However, the quasi‐monocrystalline ingot growth can lead to a different defect structure than the typical Cz‐Si process. Thus, the properties of the brand new quasi‐monocrystalline wafers, based on low and high crystal defect densities, have been for the first time studied from a mechanical point of view, comparing their strength with that of both Cz‐Si monocrystalline and typical multicrystalline materials. The study has been carried out employing the four line bending test and simulating them by means of FE models. For the analysis, failure stresses were fitted to a three‐parameter Weibull distribution. High mechanical strength was found in all the cases. However, the quasi‐monocrystalline wafers characterized by large density of bulk defects, due to the noticeable density of extended defects, showed lower fracture tensions. Copyright © 2013 John Wiley & Sons, Ltd.     

MBE growth of HgCdTe on silicon substrates for large format MWIR focal plane arrays

HgCdTe p-on-n double layer heterojunctions (DLHJs) for mid-wave infrared (MWIR) detector applications have been grown on 100 mm (4 inch) diameter (211) silicon substrates by molecular beam epitaxy (MBE). The structural quality of these films is excellent, as demonstrated by x-ray rocking curves with full widths at half maximum (FWHMs) of 80–100 arcsec, and etch pit densities from 1 10⁶ to 7 10⁶ cm⁻². Morphological defect densities for these layers are generally less than 1000 cm⁻². Improving Hg flux coverage of the wafer during growth can reduce void defects near the edges of the wafers. Improved tellurium source designs have resulted in better temporal flux stability and a reduction of the center to edge x-value variation from 9% to only 2%. Photovoltaic MWIR detectors have been fabricated from some of these 100mm wafers, and the devices show performance at 140 K which is comparable to other MWIR detectors grown on bulk CdZnTe substrates by MBE and by liquid phase epitaxy.     

Far-infrared radiation induced photovoltage of inversion electrons on GaAs and Si

We report a novel far-infrared radiation induced photoresponse of quasi two-dimensional space-charge layers on GaAs and Si in quantizing magnetic fields. In gated AlAs---GaAs heterojunctions and in metal-oxide-silicon field-effect transistors significant changes of the gate potential are observed around even Landau level filling factors, whenever radiation of a far-infrared molecular laser is absorbed at cyclotron resonance by inversion electrons. The photosignal can be understood as reflecting the difference in the inversion electron chemical potentials at two different electron temperatures. On GaAs with far-infrared laser intensities in the regime below 1mW/cm² electron temperatures are obtained that exceed the lattice temperature by up to 10K, whereas on Si at comparable conditions changes in the electron temperature are about 2 orders of magnitude smaller.     

掺镓单晶硅太阳电池和组件的光致衰减性能研究

分别使用掺镓和常规掺硼单晶硅片制备了太阳电池与组件,对电池进行了光照和空焊处理,再采用Halm电池电性能测试仪测试了两种单晶硅太阳电池和组件在光照和空焊实验前后的光电性能.实验结果表明,在相同光照条件下,采用掺镓单晶硅片所制太阳电池的光衰率比用掺硼单晶硅片的低0.91％.空焊后的掺镓单晶硅太阳电池各项光电性能参数的一致性没有出现明显变化,这有利于减少太阳电池之间的失配损失.还发现掺镓单晶硅太阳电池组件的CTM(cell to module)值高于掺硼单晶硅太阳电池组件的CTM值.总之,掺镓单晶硅太阳电池能更好地抑制光致衰减效应,并减小串焊工艺对太阳电池光电性能的影响,获得更高的太阳电池组件功率.     

Lateral growth of monocrystalline Ge on silicon oxide by ultrahigh vacuum chemical vapor deposition

The lateral growth of Ge on, both, chemically and thermally formed silicon oxide layers, from nanoscale silicon seed is studied. We have developed a method using standard local oxidation of silicon to create well-localized nanoscale silicon seeds that enable to grow Ge on thick thermal silicon oxide. The germanium growth starts selectively from the silicon seed lines and proceeds by wetting the SiO₂ layer. Analysis by high-resolution transmission electron microscopy have shown that Ge layers grown above silicon oxide were perfectly monocrystalline and are free of defect. The only detected defects are situated at the Ge/Si interface.     

Perfluorinated Subphthalocyanine as a New Acceptor Material in a Small‐Molecule Bilayer Organic Solar Cell

The complex refractive index of fluorinated subphthalocyanines (SubPcs) deposited by vacuum sublimation is determined by spectral ellipsometry. Their performance as acceptor material is characterized in a range of donor/acceptor heterojunctions in organic photovoltaic cells (OPVCs) by current–voltage measurements under 1 sun AM 1.5D simulated solar illumination and spectral response. Both electron and hole transfer between donor and acceptor materials is demonstrated. Power conversion efficiencies of 0.96% are found with an open‐circuit bias of 940 mV. Hence, it is shown that fluorinated SubPcs can be considered as an acceptor material in OPVCs with an absorption in the visible comparable to that of well‐known metallophthalocyanines.     

<Emphasis Type="Italic">In Situ</Emphasis> Interferometry of MOCVD-Grown ZnO for Nucleation-Layer-Based Optimization and Nanostructure Formation Monitoring

A reliable in situ interferometry technique allowed accurate prediction of the change in ZnO morphology during growth on various substrate types. Interferometry results showed that a 40-nm-thick nucleation layer on top of GaN allows growth of smooth and monocrystalline ZnO layers, as also confirmed by x-ray diffractometry (XRD). Studies of ZnO growth on silicon indicated that the surface morphology changes during the high-temperature growth step, resulting in needle-shaped ZnO on top of a thin ZnO initial layer. The observed surface morphology change corresponded to the interferometer signature and allowed identification of nanostructure formation.     

Electron beam induced current investigations of active electrical defects in silicon due to reactive ion etching and reactive ion beam etching processes

Reactive ion etching and reactive ion beam etching are common tools for anisotropic etch processes in silicon microdevice fabrication; but, unfortunately, they also create radiation damage in the etched surface. We have studied the electrically active defects by measuring the recombination of carriers with the help of the electron beam induced current (EBIC) mode of a secondary electron microscope. We have measured the temperature behavior of the samples by annealing studies and the temperature dependent EBIC signal for several p-doped silicon wafers and obtained different shaped curves. Theoretical EBIC models developed with the assumption of a reduced net carrier concentration in the etched areas agree with our experimental results.     

Textured silicon surface passivation by high‐rate expanding thermal plasma deposited SiN and thermal SiO2/SiN stacks for crystalline silicon solar cells

Expanding thermal plasma (ETP) deposited silicon nitride (SiN) with optical properties suited for the use as antireflection coating (ARC) on silicon solar cells has been used as passivation layer on textured monocrystalline silicon wafers. The surface passivation behavior of these high‐rate (>5 nm/s) deposited SiN films has been investigated for single layer passivation schemes and for thermal SiO₂/SiN stack systems before and after a thermal treatment that is normally used for contact‐firing. It is shown that as‐deposited ETP SiN used as a single passivation layer almost matches the performance of a thermal oxide. Furthermore, the SiN passivation behavior improves after a contact‐firing step, while the thermal oxide passivation degrades which makes ETP SiN a better alternative for single passivation layer schemes in combination with a contact‐firing step. Moreover, using the ETP SiN as a part of a thermal SiO₂/SiN stack proves to be the best alternative by realizing very low dark saturation current densities of <20 fA/cm² on textured solar‐grade FZ silicon wafers and this is further improved to <10 fA/cm² after the anneal step. Optical and electrical film characterizations have also been carried out on these SiN layers in order to study the behavior of the SiN before and after the thermal treatment. Copyright © 2008 John Wiley & Sons, Ltd.     

Directional dependence of electron blocking in PEDOT:PSS

The directional dependence of electron blocking by poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated in organic photovoltaic devices. In a conventional OPV architecture we find that a doped interlayer forms between poly(3-hexylthiophene) (P3HT) and the PSS-rich top layer of spin-coated PEDOT:PSS films. In an inverted OPV architecture, we find no mixing between PEDOT:PSS and P3HT, which is due to the lower concentration of PSS in bulk PEDOT:PSS than is found in the PSS-rich top layer. Through electrical measurements of conventional and inverted photovoltaic devices we show that the interlayer is necessary for PEDOT:PSS to be electron blocking. This result implies that PEDOT:PSS is not intrinsically electron blocking and that its directional anisotropy must be considered when comparing the advantages and disadvantages of conventional and inverted architecture photovoltaic devices.     

New method for boron removal from silicon by electron beam injection

A new method for boron removal from silicon using electron beam injection (EBI) is proposed. After thermal oxidation on monocrystalline silicon (100) wafer at 1000 °C for 1 h, EBI was used to induce thermal and negative charging effects to enhance boron diffusion in the oxide film and the silicon substrate. This facilitates boron removal from the silicon substrate. The boron concentration in samples was measured by secondary ion mass spectrometry. The results show that EBI reduced the boron concentration in the silicon substrate by 4.83%.     

Crystallographic Orientation Identification in Multicrystalline Silicon Wafers Using NIR Transmission Intensity

Near-infrared (NIR) polariscopy is a technique used for the non-destructive evaluation of the in-plane stresses in photovoltaic silicon wafers. Accurate evaluation of these stresses requires correct identification of the stress-optic coefficient, a material property which relates photoelastic parameters to physical stresses. The material stress-optic coefficient of silicon varies with crystallographic orientation. This variation poses a unique problem when measuring stresses in multicrystalline silicon (mc-Si) wafers. This paper concludes that the crystallographic orientation of silicon can be estimated by measuring the transmission of NIR light through the material. The transmission of NIR light through monocrystalline wafers of known orientation were compared with the transmission of NIR light through various grains in mc-Si wafers. X-ray diffraction was then used to verify the relationship by obtaining the crystallographic orientations of these assorted mc-Si grains. Variation of transmission intensity for different crystallographic orientations is further explained by using planar atomic density. The relationship between transmission intensity and planar atomic density appears to be linear.