Contact Technology Research Articles

A Recessed Source Contact Technology to Reduce the Specific On-Resistance of Power MOSFET on 4H-SiC

A Recessed Source Contact Technology to Reduce the Specific On-Resistance of Power MOSFET on 4H-SiC

Optimizing phosphorus-doped polysilicon in TOPCon structures using silicon oxide layers to improve silicon solar cell performance

Tunnel Oxide Passivated Contact (TOPCon) technology is one of the most influential and industrially viable solar cell technologies available today. Improving the quality of passivation contact has become a central focus of current research. Although the conventional monolayer polycrystalline silicon method is highly effective in TOPCon solar cells, it is limited by doping inhomogeneity, which impairs the passivation and electrical properties, and the cell's photovoltaic conversion efficiency remains suboptimal. To address this issue, this study investigates the deposition of two layers of silicon oxide and two layers of in-situ doped phosphorus amorphous silicon, termed double poly-Si/SiOx structures, on n-type silicon wafers using plasma-enhanced chemical vapor deposition (PECVD). The effectiveness of the structure was confirmed through various characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Key findings indicate that the double-polysilicon structure significantly enhances the uniformity of phosphorus doping, improving the carrier lifetime of the cell and reducing the contact resistance. As a result, the average efficiency in the final production stage has a conversion efficiency gain of 0.23 % over the baseline group. This study underscores the potential of this PECVD methodology to advance the fabrication of high-efficiency solar cells by providing significant improvements in passivation, doping uniformity, and overall cell performance.

Recent Advanced Ultra‐Wide Bandgap β‐Ga2O3 Material and Device Technologies

AbstractGallium oxide (Ga2O3) is an emerging ultra‐wide bandgap (UWBG) semiconductor material that has gained significant attention in the field of high voltage and high frequency power electronics. Its noteworthy attributes include a large bandgap (Eg) of 4.8 eV, high theoretical critical breakdown field strength (EC) of 8 MV cm−1, and saturation velocity (νs) of 2 × 107 cm s−1, as well as high Baliga figures of merit (BFOM) of 3000. In addition, Ga2O3 has the advantages of large‐size substrates that can be achieved by low‐cost melt‐grown techniques. This review provides a partial overview of pivotal milestones and recent advancements in the Ga2O3 material growth and device performance. It begins with a discussion of the fundamental material properties of Ga2O3, followed by a description of substrate growth and epitaxial techniques for Ga2O3. Subsequently, the contact technologies between Ga2O3 and other materials are fully elucidated. Moreover, this article also culminates with a detailed analysis of Ga2O3‐based high voltage and high frequency power devices. Some challenges and solutions, such as the lack of p‐type doping, low thermal conductivity, and low mobility are also presented and investigated in this review.

Buyer aware: Three new failure modes in TOPCon modules absent from PERC technology

The n-type tunnel oxide passivated contact (TOPCon) technology is going to be the leading industrial technology in 2024. However, there are still concerns about the reliability of TOPCon when used in the field, especially in glass/backsheet modules. This work investigates the impact of damp heat (DH) on the performance TOPCon and PERC glass/backsheet modules by varying bills of materials (BOM), such as polyolefin elastomer (POE), ethyl-vinyl acetate (EVA), and polymer backsheet options. It is found that PERC modules remain stable, with a maximum power loss (Pmax) of only 1–2%rel after 1000 h of DH testing, regardless of the BOM used. However, TOPCon modules experienced significant degradation with a drop in Pmax ranging from 4 to 65%rel after the same testing duration. Despite utilizing POE, an expensive encapsulant with a significantly lower water vapour transmission rate than EVA and devoid of acetic acid formation, a severe performance decline was observed in a specific POE variant within TOPCon modules, with a loss of power of up to 65%rel. Three types of failures were observed in TOPCon modules: point-localized failure, failure at/around the interconnection of ribbon wires and busbars, and failure throughout the whole area of cells/modules. These failures likely result from electrochemical reactions involving moisture, cell metallization, ribbon wires, contaminants, soldering flux, and additives released from POE. The observed findings underline two crucial points: 1) the vulnerability and potential failure of TOPCon solar cells when exposed to high humidity and contaminants, and 2) the high risk associated with certain POE types, which could potentially adversely affect TOPCon cells. Hence, it is crucial to exercise utmost caution and precision in handling and selecting encapsulation materials for TOPCon modules. Accordingly, urgent and extensive research efforts are crucial to substantially increase our comprehension and fortify the reliability of TOPCon cells against the pernicious effects of moisture and other contaminants.

Comparative experiment on the efficiency of water cooling in photovoltaic modules in the climatic conditions of Southern Russia

The problems of ensuring the safety of operation of nuclear power plants are always paid increased attention. In addition to the self-contained diesel generator sets used to maintain the operation of safety systems in case of loss of external power supply, it is also advisable to consider the use of more environmentally friendly self-contained photovoltaic units at this stage. The work is aimed at a comparative experimental study of the efficiency of water cooling in real natural climatic conditions of Southern Russia. In this experiment, cooled and uncooled photovoltaic modules are simultaneously exposed to a complex of variable weather factors: solar radiation, cloudiness, wind, pressure, temperature and humidity of the environment. Both modules have loads connected via MPPT controllers. The effect of water cooling on the energy efficiency of photovoltaic modules assembled from silicon heterojunction technology (HJT) solar cells was studied. The solar panels were made from 130 micron thick HJT cells interconnected using SmartWire contact technology. It reduces power loss due to possible defects such as cracks. The conditions for ensuring the highest degree of similarity between the parameters of the cooled and uncooled modules have been met. A comparative experimental study was conducted in Astrakhan State University using a long-term monitoring system for the characteristics of photovoltaic modules. This is a test photovoltaic system (TPS), built on the basis of the Paragraph PL2 electronic recorder. A significant increase in module output when working with cooling was established. At insolation of 987.5 W/m2, the power generated by the cooled module was 93.0297 W, while the power of the module without cooling was 79.306 W. The difference comprised 13.7237 watts. Power increased by 17%. In the experiment, the average efficiency value when the module was cooled was 0.15977. When uncooled, it was 0.13764. The efficiency intensified by 2.21%. This increase is significant. The results obtained confirm the fairly high efficiency of water cooling in photovoltaic modules in real natural operating conditions for regions with high ambient temperatures, Southern Russia, in particular

Enhancement of efficiency in monocrystalline silicon solar cells

As the representative of the first generation of solar cells, crystalline silicon solar cells still dominate the photovoltaic market, including monocrystalline and polycrystalline silicon cells. With the development of silicon materials and cut-silicon wafer technologies, monocrystalline products have become more cost-effective, accelerating the replacement of polycrystalline products. In addition, the conversion efficiency of monocrystalline products increases gradually through high-efficiency cell technologies such as Passivated Emitter and Rear Cell (PERC). This paper will start with the solar cell efficiency and combine cost factor, the P-type PERC cell and additional four types of high-efficiency N-type cell technologies to improve the conversion efficiency for exploration, and will analyze and predict the future solar cell industrialization technologies. The study finally concludes that the N-type Tunnel Oxide Passivated Contact solar cell technology has a large industrial potential and could become a mainstream technology after the perc cell technology. At the same time, Interdigitated back contact cell structure and selective all-passive contact technologies are reliable paths to obtain solar cells with high conversion efficiency, integrated cost, and efficiency, depending on the advantages and compatibility of various cells. It can create conditions for the industrialization of low- cost and high-efficiency monocrystalline silicon solar cells.

Low contact resistance of NiGeSn on n-GeSn

A systematic investigation of the NiGeSn formation and its contact resistivity with GeSn semiconductors are studied. The method of investigation is based on the circular transmission line measurement (CTLM) geometry. The optimum NiGeSn formation temperature is 325 °C, offering a lower contact resistivity of 4.15 × 10−5 Ω·cm2 on n-GeSn. The elemental diffusion mechanism during the NiGeSn formation is also discussed. In line with the research of new materials for cryogenic electronics, GeSn shows a low contact resistivity of 1.79 × 10−5 Ω·cm2 at 5 K. These findings offer valuable insights into optimizing GeSn-based contact technologies for both low-power and cryogenic applications.

Physics-informed machine learning models for the prediction of transient temperature distribution of ferritic steel in directed energy deposition by cold metal transfer

In-situ monitoring of the additive layer characteristics in the directed energy deposition (DED) process by any contact technology is cumbersome. A well-tested finite element (FE) model is often employed to extract transient temperature distribution during deposition. However, the numerical model pertaining to each deposition attribute is computationally expensive. In the present work, we have generated a dataset through an experimentally validated thermal model, and further multiple machine learning (ML) algorithms are applied to train datasets. Models with an accuracy of more than 99% are utilised for the prediction of transient temperature distribution. The validation of deposition attributes using experiments and numerical model suggests that the physics-informed machine learning models for cold metal transfer can be applied in the DED process.

Ohmic Contact to n-GaN Using RT-Sputtered GaN:O.

One of the key issues in GaN-based devices is the resistivity and technology of ohmic contacts to n-type GaN. This work presents, for the first time, effective intentional oxygen doping of sputtered GaN films to obtain highly conductive n+-GaN:O films. We have developed a novel and simple method to obtain these films. The method is based on the room temperature magnetron sputtering of a single crystal bulk GaN target doped with oxygen. The n+-GaN:O films exhibit a polycrystalline structure with a crack-free surface and a free electron concentration of 7.4 × 1018 cm3. Ohmic contact to GaN:Si with n+-GaN:O sub-contact layer achieves specific contact resistance of the order of 10-5 Ωcm2 after thermal treatment. The obtained results are very promising for the development of the technology of a whole new class of ohmic contacts to n-GaN.

Failure time of reinforced concrete column under blast load

To explore the damage and the failure time of the reinforced concrete column in an adjacent physical field of explosion, a comprehensive finite element model of TNT-air-column in the software LS-DYNA is set up in consideration of the advanced numerical simulation technologies (i.e., element birth and death technology, large deformation technology, contact technology, etc) and the strain rate effects of the concrete and steel materials. First of all, an explosion test is conducted on two scale models of the reinforced concrete column, and the finite element model is validated by comparing the numerical simulation results with the experimental data. The failure process, failure mode, and failure criterion of the reinforced concrete column under blast load are further investigated. Thereafter, a series of parameter studies are conducted to investigate the damage and the failure time of the reinforced concrete column. Finally, a new method is proposed to estimate the failure time of the reinforced concrete column and the corresponding basic steps are given in this study. Through the researches and analyses of the typical cases, the results show that the failure modes change from punching failure to compression-flexure failure via compression-shear failure with the increase in the scaled distance. The medium damage and the high damage occur mostly on the reinforced concrete column in an adjacent physical field of explosion. The damage index of the reinforced concrete column varies significantly with the compressive strength of concrete, column height, column depth, longitudinal reinforcement ratio, transverse reinforcement ratio, and axial compression ratio, especially the column depth and the axial compression ratio; however it has little relation with the column width. The failure time of the reinforced concrete column is up to tens of milliseconds or even more than one hundred milliseconds. The calculation formulas used in the proposed method are based on previous research and simulation results. The proposed method is rigorous and thorough and the predicted results are highly accurate and effective. Besides, this method can provide a good prediction of the failure time of the reinforced concrete columns with different axial compression ratios.

Performance improvement with non-alloyed ohmic contacts technology on AlGaN/GaN High Electron Mobility Transistors on 6H-SiC substrate

In this paper, non-alloyed ohmic contacts regrown by molecular beam epitaxy (MBE) are fabricated on AlGaN/GaN high-electron-mobility transistors on 6H-SiC substrate. Low ohmic contact resistance of 0.13 Ω.mm is obtained. This paper demonstrates the high frequency and high power performance improvements thanks to this technology regarding conventional technology based on alloyed ohmic contacts. The fabricated device with a 75-nm-T-shaped gate demonstrates a maximum drain current density of 1.1 A/mm at VGS = 1 V and a peak transconductance gm of 464 mS/mm. A current gain cut-off frequency fT of 110 GHz and a maximum oscillation frequency fMAX of 150 GHz are achieved. At VDS = 25 V, continuous-wave output power density of 3.8 W/mm is achieved at 40 GHz associated with 42.8% power-added efficiency and a linear power gain of 6 dB. A maximum power-added efficiency of 55% is also obtained at VDS = 20 V.

Engineering Silicon Interfaces with Transparent AlyTiOx/ZnO/TiO2 Stack Exhibiting Exceptional Passivating Contact Performance

AbstractPassivating contact technologies are essential for fabricating high‐efficiency crystalline silicon (c‐Si) solar cells, and their application and incorporation into manufacturing lines has ranked as a hot topic of research. Generally, ideal passivating contacts should combine excellent electrical contact, outstanding surface passivation, and high optical transparency. However, addressing all these criteria concurrently is challenging since it is unlikely for any single material to exhibit both efficient carrier transport and surface‐defect passivation while demonstrating negligible parasitic absorption. In this work, several earth‐abundant, wide‐bandgap materials are combined to engineer high‐quality transparent electron‐selective passivating contact structures capable of overcoming these obstacles. A highly transparent AlyTiOx/ZnO/TiO2 stack with a total thickness of 3 nm, prepared by atomic layer deposition, is shown to provide a close‐to‐ideal passivating contact to Si surfaces by enabling dual functions of remarkable silicon surface passivation (with an effective minority carrier lifetime of 12.3 ms, an implied open‐circuit voltage of 730 mV, and a surface recombination current density prefactor of 2.6 fA cm−2), combined with efficient carrier transport with a very low contact resistivity of 3.4 mΩ cm2. These results demonstrate that low‐cost silicon interface‐engineering strategiesbased on transition metal oxides can push c‐Si solar cell performance to its theoretical limits.

Improvement in the Performance of P-Type Tunnel Oxide Passivated Contact Solar Cell With Selective Tunneling Junctions Underneath the Contacts on Front Side

Industrial silicon solar cells are now moving further from passivated emitter and rear contact (PERC) toward Tunnel Oxide Passivated contact (TOPCon) technology. The efficiency of the PERC solar cell is improved by TOPCon technology, in which the rear side is fully passivated by an oxide/poly-Si tunneling junction. The performance of a TOPCon solar cell may further be improved by the incorporation of selective tunneling junctions underneath the front contacts. Some fabrications have been reported on a similar structure for an n-type Si substrate but they have not achieved the expected results. Also, a detailed study has not been done yet. Using 3-D sentaurus technology computer aided design (TCAD) simulation software, a detailed analysis has been done on the modified structure through the optimization of the tunnel oxides, the interfaces, the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> poly-Si layer, the selective (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> -poly-Si) tunneling junctions underneath the front contacts, etc., which has not been done earlier. It is seen that a thick n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> poly-Si layer causes parasitic absorption of light, whereas a very thin poly-Si layer cannot provide sufficient field for tunneling of carriers. A thicker tunnel oxide produces a high series resistance, whereas a very thin tunnel oxide cannot restrict the minority carriers to reach to the contacts. Therefore, an optimization is required and the optimization is done based on a fabricated bifacial p-TOPCon solar cell reported in the literature with an efficiency of 21.2% and bulk lifetime of 200 μs. After performing all the modifications in the fabricated reference cell and optimizing different parameters, the efficiency is improved by 3.5% in absolute. The efficiency is further improved to 25.4% with the bulk lifetime of 1 ms.

Editorial: Passivating contact solar cells

In the last decade, significant attention has been given to the concept of passivating contact solar cells. Such cells are characterised by very low contact recombination and low contact resistance, a combination that is challenging to achieve with conventional diffused silicon layers. These cells demonstrate a very high open-circuit voltage and therefore higher efficiency. Passivating contacts can be classified into three main technologies according to the material used for the charge-carrier selection: (i) doped amorphous silicon; (ii) doped polycrystalline silicon; and (iii) metal compounds and organic materials. Due to the impressive progress of passivating contacts and the wide variety of technologies and approaches, Progress in Photovoltaic decided to dedicate an entire issue to reviewing the status of this concept. The issue starts with a review of the three main technologies of passivating contacts, summarising their current efficiencies and discussing their distinctive features, advantages, and limitations. While doped amorphous silicon has been used for the manufacturing of industrial heterojunction solar cells for decades, polycrystalline silicon-based solar cells have only recently entered mass production. Interestingly, this technology was introduced to bipolar transistors as early as the 1970s and adapted into silicon solar cells in the 1980s. However, because some aspects other than the contacts limited the obtainable solar cell efficiencies, this technology was not actively investigated until 2013. Nevertheless, since then, a substantial amount of research has been done by several research institutes and companies, enhancing the performance of polycrystalline silicon-based solar cells to efficiencies above 26%. More importantly, significant effort has been made to commercialise this technology with significant progress already reported by several photovoltaic companies. As doped polycrystalline silicon seems to be the most mature passivating contact technology, we review the status of the three leading approaches: The POLO of ISFH, the TOPCon of Fraunhofer ISE, and the monoPoly of SERIS. With several large manufacturers announcing their plans to transfer polycrystalline silicon-based technology into mass production, we also review the activities that have been taken to push the boundaries of this technology and enabled its integration into existing production lines. Manufacturing options, as well as necessary technological advances in cell metallisation and module integration, are discussed from the industrial perspective. We then review the progress of passivating contact technologies that employ metal compounds as the carrier-selective layer. The interest in this technology has recently increased with a few promising families of materials having demonstrated excellent results, specifically alkali/alkaline-earth metal compounds and transition-metal oxides. The number of successful demonstrations of selective-contact materials within these families is increasing fast, with the best solar cell efficiencies now exceeding 23%. The challenges of this technology to be considered for industrial adoption are then discussed, together with its prospects in the context of silicon photovoltaics. In a separate paper, we provide a detailed techno-economic analysis of the use of atomic layer deposited transition-metal oxides for the fabrication of silicon solar cells. The special issue concludes with a paper discussing the challenges and opportunities in the metallisation of industrial perovskite/silicon tandem solar cells. We want to thank all the authors for their great contributions. It was a pleasure to work with such a talented and diverse group of researchers. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

Impact of Graphene Monolayer on the Performance of Non-Conventional Silicon Heterojunction Solar Cells with MoOx Hole-Selective Contact.

In this work, a new design of transparent conductive electrode based on a graphene monolayer is evaluated. This hybrid electrode is incorporated into non-standard, high-efficiency crystalline silicon solar cells, where the conventional emitter is replaced by a MoOx selective contact. The device characterization reveals a clear electrical improvement when the graphene monolayer is placed as part of the electrode. The current-voltage characteristic of the solar cell with graphene shows an improved FF and Voc provided by the front electrode modification. Improved conductance values up to 5.5 mS are achieved for the graphene-based electrode, in comparison with 3 mS for bare ITO. In addition, the device efficiency improves by around 1.6% when graphene is incorporated on top. These results so far open the possibility of noticeably improving the contact technology of non-conventional photovoltaic technologies and further enhancing their performance.

Approaching the quantum limit in two-dimensional semiconductor contacts.

The development of next-generation electronics requires scaling of channel material thickness down to the two-dimensional limit while maintaining ultralow contact resistance1,2. Transition-metal dichalcogenides can sustain transistor scaling to the end of roadmap, but despite a myriad of efforts, the device performance remains contact-limited3-12. In particular, the contact resistance has not surpassed that of covalently bonded metal-semiconductor junctions owing to the intrinsic van der Waals gap, and the best contact technologies are facing stability issues3,7. Here we push the electrical contact of monolayer molybdenum disulfide close to the quantum limit by hybridization of energy bands with semi-metallic antimony ([Formula: see text]) through strong van der Waals interactions. The contacts exhibit a low contact resistance of 42 ohm micrometres and excellent stability at 125 degrees Celsius. Owing to improved contacts, short-channel molybdenum disulfide transistors show current saturation under one-volt drain bias with an on-state current of 1.23 milliamperes per micrometre, an on/off ratio over 108 and an intrinsic delay of 74 femtoseconds. These performances outperformed equivalent silicon complementary metal-oxide-semiconductor technologies and satisfied the 2028 roadmap target. We further fabricate large-area device arrays and demonstrate lowvariability in contact resistance, threshold voltage, subthreshold swing, on/off ratio, on-state current and transconductance13. The excellent electrical performance, stability and variability make antimony ([Formula: see text]) a promising contact technology for transition-metal-dichalcogenide-based electronics beyond silicon.

Investigation of the Influence of Design Parameters on the Strength of Steel–Concrete Composite Shear Walls by Finite Element Simulations

In this paper, the influence of design parameters on the strength of steel–concrete composite shear walls is investigated by means of finite element (FE) simulations. The shear wall typology studied in this paper consists of multiple composite plate shear wall-concrete encased on one or both sides of the plates. The FE models include contact technology to capture debonding between concrete and steel, tensile cracking in concrete, and large deflection theory involving local instabilities. Some design parameters considered in this work are the height-to-width ratio of the steel plates and their thickness, number of steel plates, the cross-section of the columns, and the height-to-width ratio of the shear wall. Furthermore, a sensitivity analysis of the normalised shear strength per unit cost of structure for these design parameters is also studied. Our numerical predictions are validated successfully with experimental data reported in the literature, revealing the predictive capabilities of the model. The present results provide further insight into the structural behavior of steel–concrete composite shear walls and pave the way for the future development of more efficient and innovative steel–concrete composite systems.

Interdigitated Back Contact Technology as Final Evolution for Industrial Crystalline Single-Junction Silicon Solar Cell

We present our own Interdigitated Back Contact (IBC) technology, which was developed at ISC Konstanz and implemented in mass production with and at SPIC Solar in Xining, China, with production efficiencies of over 24%. To our knowledge, this is the highest efficiency achieved in the mass production of crystalline silicon solar cells without the use of charge-carrier-selective contacts. With an adapted screen-printing sequence, it is possible to achieve open-circuit voltages of over 700 mV. Advanced module technology has been developed for the IBC interconnection, which is ultimately simpler than for conventional double-sided contacted solar cells. In the next step, we will realize low-cost charge-carrier-selective contacts for both polarities in a simple sequence using processes developed and patented at ISC Konstanz. With the industrialisation of this process, it will be possible to achieve efficiencies well above 25% at low cost. We will show that with the replacement of silver screen-printed contacts by copper or aluminium metallisation, future IBC technology will be the end product for the PV market, as it is the best performing c-Si technology, leading to the lowest cost of electricity, even in utility-scale applications.

The silver learning curve for photovoltaics and projected silver demand for net‐zero emissions by 2050

AbstractThe clean energy transition could see the cumulative installed capacity of photovoltaics increase from 1 TW before the end of 2022 to 15–60 TW by 2050, creating a significant silver demand risk. Here, we present a silver learning curve for the photovoltaic industry with a learning rate of 20.3 ± 0.8%. Maintaining business as usual with a dominance of p‐type technology could require over 20% of the current annual silver supply by 2027 and a cumulative 450–520 kt of silver until 2050, approximately 85–98% of the current global silver reserves. A rapid transition to higher efficiency tunnel oxide passivated contact and silicon heterojunction cell technologies in their present silver‐intensive forms could increase and accelerate silver demand. As we approach annual production capacities of over 1 TW by 2030, addressing the silver issue requires increased efforts in research and development to increase the silver learning rate by 30%, with existing silver‐lean and silver‐free metallisation approaches including copper plating and screen‐printing of aluminium and copper.

Finite Element Simulation of HELICOIL® Inserts

This paper details the possibility of simulating HELICOIL® inserts using Finite Element Analysis and contact technology. The main procedure is based on the use of contact elements in the Glue–Cohesive setting, which is usually considered for the simulation of composites. The contact represents the behaviour of an interface, including the HELICOIL® insert, the sample threads, and the screw threads. The behaviour of the cohesive contact is determined by a multi-linear curve, and is described by several parameters. Our main goal is to determine the number of parameters and their values to provide a defined accuracy. The sample is made of ABS-M30 material, while the screw is made of steel. The Finite Element Model Updating method is used to determine the parameters from experimental data. The problem regarding the addition of a point (parameter) to a multi-linear curve is solved using the principle of halving intervals. A gradient approach combined with a penalisation method is used to identify the parameters of the interface model. The simulation results are compared with data obtained through Digital Image Correlation measurements.