21.0%‐efficient co‐diffused screen printed n‐type silicon solar cell with rear‐side boron emitter

Plasma enhanced chemical vapor deposition (PECVD) is applied to deposit boron silicate glasses (BSG) acting as boron diffusion source during the fabrication of n‐type silicon solar cells. We characterize the resulting boron‐diffused emitter after boron drive‐in from PECVD BSG by measuring the sheet resistances R_sheet,B and saturation current densities J_0,B. For process optimization, we vary the PECVD deposition parameters such as the gas flows of the precursor gases silane and diborane and the PECVD BSG layer thickness. We find an optimum gas flow ratio of SiH₄/B₂H₆= 8% and layer thickness of 40 nm. After boron drive in from these PECVD BSG diffusion sources, a low J_0,B values of 21 fA/cm² is reached for R_sheet,B = 70 Ω/□. The optimized PECVD BSG layers together with a co‐diffusion process are implemented into the fabrication process of passivated emitter and rear totally diffused (PERT) back junction (BJ) cells on n‐type silicon. An independently confirmed energy conversion efficiency of 21.0% is achieved on 15.6 × 15.6 cm² cell area with a simplified process flow. This is the highest efficiency reported for a co‐diffused n‐type PERT BJ cell using PECVD BSG as diffusion source. A loss analysis shows a small contribution of 0.13 mW/cm² of the boron diffusion to the recombination loss proving the high quality of this diffusion source. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

用四探针及阳极氧化方法测量硅中扩散层杂质分布

本文讨论了:(1)用阳极氧化法在硅片表面去层的技术;(2)用四探针测量扩散层面电导的方法;(3)用阳极氧化去层及四探针测量面电导方法求得扩散层精细杂质分布。文中着重讨论了实验技术中的实际问题,如如何在阳极氧化过程中取得精细而均匀的去层(300—1500?);如何控制及测量去层厚度;测量面电导及杂质分布时的误差来源及减小误差的措施。以典型的磷在硅中扩散的杂质分布测量为例:扩散深度为4.9μm,测量间距为400—1600?,面电导测量误差估计小于3％,杂质分布误差估计小于20％。简单地提出了一些测量中尚待进一步解决的问题。     

GaAs1-xPx中混晶无序与Fe深中心的性质

对不同组分的掺FeⅢ-Ⅴ族混晶GaAs1-xPx,测量了Fe深受主中心空穴热发射的非指数恒温暗电容瞬态及DLTS谱。用混晶无序使Fe深能级展宽的模型理论拟合实验结果,得到Fe能级Gauss型展宽的半宽和中心能级的热发射率,并确定出基态空穴跃迁的中心能级的焓变与组分的关系:先是减少,而后增大,与由光电容方法得到的Gibbs自由能变量与组分x的关系明显不同。 进一步讨论表明,上述两种测量方法得到的Fe中心的激活能不同,可能反映Fe中心的键合状态和混晶无序诱导的品格弛豫的影响。     

Diamond deposition on siliconized stainless steel

Silicon diffusion layers in AISI 304 and AISI 316 type stainless steels were investigated as an alternative to surface barrier coatings for diamond film growth. Uniform 2 μm thick silicon rich interlayers were obtained by coating the surface of the steels with silicon and performing diffusion treatments at 800 °C. Adherent diamond films with low sp² carbon content were deposited on the diffused silicon layers by a modified hot filament assisted chemical vapor deposition (HFCVD) method. Characterization of as-siliconized layers and diamond coatings was performed by energy dispersive X-ray analysis, scanning electron microscopy, X-ray diffraction and Raman spectroscopy.     

Ti:LiNbO3 optical waveguides

Various experiments on Ti diffused optical waveguides in LiNbO₃ have been carried out in order to determine precisely the character of the diffusion process. The required guide parameters and the effective mode indices could be controlled by adjusting only the diffusion time under fixed temperature and film thickness. Therefore the dependence of the guide characteristics on the diffusion time has been investigated in detail. On the basis of the data obtained, a two-stage diffusion model is proposed. In the first stage, the Ti diffusant profile is described by a erfc-function, and the second stage is characterized by a modified Gaussian form.     

Diffusion interaction between Al and Mg controlled by a high magnetic field

The effects of an 11.5 T high magnetic field on the growth behavior of compounds layers during reactive diffusion in solid Al/solid Mg diffusion couples have been investigated. After annealing with and without a magnetic field, the interfacial zone was still composed of two layers of stable compounds β (Mg₂Al₃) and γ (Mg₁₇Al₁₂), but the thicknesses of the layers were increased by the magnetic field. Data analysis of the thicknesses of compound layers showed that the growth of the γ layer was controlled by grain boundary diffusion as well as volume diffusion at B=0 T, but only controlled by volume diffusion when an 11.5 T high magnetic field was applied. The interdiffusion coefficients for the samples annealed at 643–693 K were calculated from the parabolic relationship between the migration of the interface and the annealing time. The results show that the diffusion constant increased due to the high magnetic field, increasing the chemical potential gradient, and in turn it caused the interdiffusion coefficient to increase.     

刚性光纤元器件芯,皮玻璃的相互散

通过扫描电子显微镜观察到刚性光纤元器件芯、皮玻璃之间有扩散层,用干涉仪测量了扩散层的折射率范围。本文从玻璃网络结构观点解释了这一扩散机理,并就刚性光纤元器件芯、皮玻璃配方设计中如何使离子扩散减到最小程度提出了可行性措施。     

Thermal Diffusion Process Estimation for Fabrication of Graded Plastic Optical Fibre

Thermal diffusion of dopants is investigated in the process of generating the graded-index profile of plastic optical fibres. Because the diffusion coefficient in high polymers has been shown to depend strongly on dopant concentration, it is allowed in this work to vary with the radial coordinate of the multistep-core fibre. A novel multi-layer model is presented for solving the diffusion equation with the variable diffusion coefficient. It is solved by the finite difference method. The solution determines the dopant diffusion profile in the fibre. It is verified against a solution from the literature and two cases of fibres with diffused profiles. The application is demonstrated on two examples of graded-index plastic optical fibres, one originally with a two-step and the other with four-step core. The results indicate that closer to the core-cladding interface, the computed diffused profile with variable diffusion coefficient D is closer to target profile than the profile obtained with constant D for the same time of thermal process.     

Diffusion of silicon in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained film structure (B ₊ films) have been examined as diffusion barriers, preventing the silicon diffusion in silicon devices. The silicon diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) after annealing at temperatures up to 900° C, in view of application of high-temperature processes. The diffusivity from 400 to 900° C: D (m² s^–1)=2.5×10^–18 exp[–31 kJ/mol/(RT)] in B ₀ layers and D (m² s^–1)=3×10^–19 exp[–26 kJ/mol/(RT) in B ₊ TiN layers. The diffusivities determined correspond to grain boundary diffusion, the difference being due to the different microstructure. The very low diffusivity of silicon in B ₊ TiN layer makes it an excellent high-temperature barrier preventing silicon diffusion.     

Determination of electron-diffusion length from photocurrent characteristics of the structure ITO/a-SiC:H(p-type)/a-Si:H/a-Si:H(n-type)/Pd

In this study the electron diffusion length L _n is determined from the relative spectral response of the photocurrent characteristics of the p/i/n sandwich structure ITO/a-SiC:H(p-type)/a-Si:H/a-Si:H(n-type)/Pd. The techniques used for the preparation of the a-Sic:H and a-Si:H amorphous films were glow-discharge and rf magnetron sputtering, respectively. The thickness of the p-type, intrinsic and n-type layer were 400 Å, 7000 Å and 600 Å, respectively. The response of the short-circuit current density J _sc was measured versus the photon energy hv at both constant light intensity and constant temperature. The electron diffusion length was found to be 0.31 m by means of the method of Agarwala and Tewary. Although, in the case of single crystals many diffusion length measurements have been made, there are only few papers for amorphous silicon this films [1]. As it is well-known, the diffusion length of the charge carriers is the most important parameter from the point of view of solar cell applications [2]. In order to obtain a high efficiency in a solar cell all carriers created under illumination in the intrinsic layer should reach the electrodes [3]. In the case that the thickness of the intrinsic layer is much larger than the diffusion length, not all carriers can reach the electrodes and, accordingly, a low efficiency results [4]. On the other hand, carriers which reach the electrodes without thermalizing do not contribute to the photocurrent and finally the efficiency of the solar cell is negatively affected. In order to avoid such an effect to a large extent, the thickness of the amorphous layers in a p/i/n solar cell must be conveniently chosen compared to the diffusion length of the carriers.Here it is aimed to determine the electron diffusion length. In order to achieve this goal, the photocurrent characteristics of an ITO/a-SiC:H(p-type)/a-Si:H/a-Si:H(n-type)/Pd structure was measured versus the photon energy at constant light intensity and constant temperature. In order to determine the electron diffusion length, the method of Agarwala and Tewary [5] was utilized.     

MgF2作为镁离子内扩散LiNbO3单晶扩散源的研究

利用ＭｇＦ₂作为扩散源进行镁离子内扩散ＬｉＮＯ₃单晶基片的研究．经电子探针显微镜分析表明，镁的扩散层镁离子浓度分布具有近似半抛物形和阶跃形分布，并得到镁的激活能为１０４ＫＪ／mol.X射线衍射分析发现，当镁离子内扩散超过一定程度时，在镁的扩散层出现具有ＬｉＮｂ₃Ｏ₈的物相结构，并发现该物相结构的出现与ＬｉＮＯ₃体内锂离子的外扩散和扩散表面氟离子的存在有关．由扫描电子显微镜观察到氟离子以ＬｉＦ的形式出现，并随着扩散程度的增大，挥发和脱离开扩散层表面． 关键词：     

Non-equilibrium point defect phenomena influencing beryllium and zinc diffusion in GaAs and related compounds

Beryllium and zinc are the main p-type dopants used for the fabrication of devices based on GaAs or related III-V materials. Both elements are substitutionally dissolved on the group III sublattice and diffuse via the kick-out mechanism which involves group III self-interstitials. Non-equilibrium concentrations of these self-interstitials have a strong influence on the diffusivities of Be and Zn with often drastic consequences on device behavior especially if Be or Zn is used to realize narrow base regions in heterojunction bipolar transistors (HBTs). Various situations in which non-equilibrium point defects play a role for Be and Zn diffusion are discussed such as: in-diffusion of these dopants from an outside source, diffusion of grown-in dopants, self-interstitial generation by Fermi level surface pinning of highly n ⁺-doped emitter cap or subcollector layers in HBTs, or recom bination-enhanced beryllium diffusion during device operation. Finally, we will comment on the diffusion behavior of carbon, which is dissolved on the group V sublattice in GaAs, is much less sensitive to non-equilibrium point defect, and, therefore, is increasingly used to replace Be and Zn as p-type dopants.On sabbatical leave from Duke University, School of Engineering, Durham, NC 27706, USA     

Mn-including InAs quantum dots fabricated by Mn implantation

Mn-including InAs quantum dots (QDs) were fabricated by Mn-ion implantation and subsequent annealing. The optical, compositional, and structural properties of the treated samples were analyzed by photoluminescence (PL) and microscopy. Energy dispersive X-ray (EDX) results indicate that Mn ions diffused from the bulk GaAs into the InAs QDs during annealing, and the diffusion appears to be driven by the strain in the InAs QDs. The temperature dependence of the PL of Mn-including InAs QD samples exhibits QDs PL characteristics. At the same time, the heavy Mn-including InAs QD samples have ferromagnetic properties and high T_c.     

A method for the study of surface corrosion beneath protective layers

This work is concerned with the development of a technique to observe the onset of corrosion as it occurs beneath a temporary protective layer. Such temporary protectives include paints, varnishes, greases and oils that are applied to metal surfaces to give short-term protection from corrosion. The objective of this project was to develop a technique that could be used to evaluate the effectiveness of various temporary protectives in different environments, without the need to remove the protective layer, thus eliminating the possibility of any chemical changes or loss of corrosion products occurring as a result of removal. The temporary protective layers are typically 25Μm for paints and 15Μm per layer for varnishes. The 6.3 keV fluorescence X-ray is able to penetrate such layers, but the large escape depth (∼10Μm) of the X-rays means that for a thin protective layer a large proportion of the X-rays detected will originate from deep within the substrate and the resultant spectrum will be representative of the bulk rather than the surface. To enhance the surface sensitivity of the CXMS technique, the near surface region must be enriched in the isotope Fe-57. To achieve this, Fe-57 was vacuum evaporated onto the surface of mild steel substrates and subsequently diffused into the near surface region. An approximate 20 nm Fe-57 layer was deposited onto mild steel samples. The surface enriched samples were then annealed to allow the Fe-57 to diffuse into the near surface region of the mild steel substrate, and also to allow back diffusion of the substrate. A diffusion model was developed to predict the surface distribution of Fe-57 as a function of annealing parameters. The computer diffusion model allowed the ideal annealing conditions to be estimated to obtain a required near surface environment. It was essential that the annealing conditions did not result in any surface oxidation, and did result in a surface that was characteristic of mild steel. CEMS and CXMS spectra were recorded of samples before and after annealing, and also dynamic Secondary Ion Mass Spectrometry (SIMS) was used to monitor the enrichment and diffusion process. Energy Dispersive X-ray Analysis (EDXA) was also used to characterize the surface. A number of enriched samples were prepared and treated with a variety of surface temporary protectives. The CXMS spectra were recorded before and after exposure of the coated samples to various aggressive environments.     

Copper diffusion in TaN-based thin layers

The diffusion of Cu through TaN-based thin layers into a Si substrate has been studied. The barrier efficiency of TaN/Ta/TaN multilayers of 150 nm in thickness has been investigated and is compared with that of TaN single layers. Thermal stabilities of these TaN-based thin layers against Cu diffusion were determined from in situ X-ray diffraction experiments, conducted in the temperature range of 773-973 K. The TaN/Ta/TaN barrier appeared to be more efficient in preventing Cu diffusion than the TaN single layer.     

The temperature dependence of the perpendicular giant magnetoresistance in Co/Cu multilayered nanowires

A theory, based on earlier work by Valet and Fert, is first presented to describe the influence of temperature on the perpendicular giant magnetoresistance (GMR) in multilayers. Then we present GMR measurements performed at T=77 K and at room temperature on Co/Cu multilayered nanowires with layer thicknesses ranging from a few nm to 1 μm. We use our model to obtain a good quantitative fit to the experimental results in both the short spin diffusion length limit and out of this limit. We discuss the temperature dependence of the bulk parameters, the scattering spin asymmetry coefficient and spin diffusion length in the Co layers. Received: 25 January 1998 / Accepted: 6 May 1998     

Development of polycrystalline silicon films on flexible metallic substrates by aluminium induced crystallization

Thin film silicon solar cells on low cost foreign substrates could be attractive for highly efficient and low cost production of photovoltaic electricity. An attempt has been made to synthesise high-quality continuous polycrystalline silicon (pc-Si) layers on flexible metallic substrates using aluminium induced crystallization (AIC) for the first time. Amorphous silicon films deposited by ECR-PECVD were crystallized on diffusion barrier coated metallic substrates at lower temperatures (<577°C). The crystallization was studied using Raman as well as UV reflectance spectroscopy. The as-grown AIC pc-Si films were found to be continuous and densely packed without amorphous phase. The migration of impurities from the substrate to the pc-Si films and the conformability of the barrier layer with the substrate and pc-Si films were studied systematically in terms of chemical and stress level analysis, which are the important aspects to be considered when metallic foils are used as substrates. It was observed that the barrier layer also serves as a buffer layer to minimise the stress level enormously in the AIC grown pc-Si layer, though the supporting material has a thermal expansion coefficient of higher order at higher annealing temperatures. The present investigation proves the possibility to grow better-quality polycrystalline silicon films on flexible metallic foils and further demonstrates the steps that need to be considered to improve the quality of AIC pc-Si films as well as the strength of the barrier layer.     

Surface characterisation and interface studies of high-k materials by XPS and TOF-SIMS

High-k dielectric LaAlO₃ (LAO) films on Si(100) were studied by TOF-SIMS and XPS to look for diffusion processes during deposition and additional thermal treatment and for the formation and composition of possible interfacial layers. The measurements reveal the existence of SiO₂ at the LAO/Si interface. Thermal treatment strengthens this effect indicating a segregation of Si. However, thin LAO layers show no interfacial SiO₂ but the formation of a La-Al-Si-O compound. In addition, Pt diffusion from the top coating into the LAO layers occurs. Within the LAO layer C is the most abundant contamination (10²¹ at/cm³). Its relatively high concentration could influence electric characteristics. XPS shows that CO₃²⁻ is intrinsic to the LAO layer and is due to the adsorption of CO₂ of the residual gas in the deposition chamber.     

Zinc diffusion in GaAs and zinc-induced disordering of GaAs/AlGaAs multiple quantum wells: a multitechnique study

A review of experimental results obtained by different techniques is presented on the problem of zinc diffusion. Zinc diffusion was carried out on Si-doped GaAs (n10¹⁸ cm^–3) and on multiple quantum well (MQW) structures. The samples were investigated by secondary-ion mass spectroscopy (SIMS), different imaging modes of scanning electron microscopy such as secondary electrons, cathodoluminescence (CL) and electron beam-induced current (EBIC), transmission electron microscopy on a wedge-shaped specimen (WTEM) and by photoluminescence (PL). A nonexponential decay of the low-temperature EBIC signal accompanied by a very low CL signal due to the high density of nonradiative recombination centres were observed in the diffused region of the n-doped GaAs. Indeed, PL measurements demonstrate that Ga vacancies play a key role on the mechanism of the Zn diffusion. On the impurity-induced disordered (IID) MQW samples, an enrichment of Al at the surface was observed by SIMS and confirmed by WTEM and PL. Low-temperature PL spectra show the gradual disappearance of the MQW excitonic transitions as the number of disordered layers increases. When all of the MQW structure is destroyed, the band-to-band recombinations in the IID produced alloy dominate the PL spectrum.     

氧气氛中p-GaN/Ni/Au电极在相同温度不同合金时间下的欧姆接触形成机制和扩散行为

用卢瑟福背散射/沟道技术研究了p-GaN上的Ni/Au电极在氧气氛下相同合金温度(500℃)不同合金时间后的微结构演化,以揭示欧姆接触的形成机制.利用背散射随机谱和RUMP模拟程序研究了电极金属之间的互扩散,用沟道谱探测了电极金属中的氧分布.结合不同合金时间下比接触电阻ρ_c的变化,发现随着合金时间的延长比接触电阻持续降低,在合金时间60 s后降低的速度减慢, Au扩散到GaN的表面,在p-GaN上形成外延结构,O向电极内部扩散反应生成NiO对降低ρ_{关键词： GaN 卢瑟福背散射/沟道 欧姆接触}