Contact Windows Research Articles

The Influence of Rapid Heat Treatment During the Formation of Aluminum-Polysilicon Contacts on the Electrical Parameters of CMOS Microcircuits

The influence of rapid heat treatment (450 °C, 7 s) on the electrical parameters of CMOS integrated circuits during the formation of ohmic contact between aluminum metallization and polysilicon is considered. The following volt-ampere characteristics of the dependence of drain current on voltage were chosen as the analyzed parameters of n- and p-channel transistors: at the gate when diode-connected; on the drain at different gate voltages; on the drain in the channel breakdown mode without applying potential to the gate. A comparison of these parameters was carried out with respect to microcircuits manufactured using standard technology (450 °C, 20 min) to form these contacts. Analysis of the results showed that the use of rapid heat treatment to form an ohmic aluminum-polysilicon contact can significantly improve the above characteristics of n-MOS and p-MOS transistors. From the current-voltage characteristics of n- and p-channel transistors it follows that in the region of gate voltages greater than 0.65 V, the drain current after long-term heat treatment is higher than after quick heat treatment. Analysis of the current-voltage characteristics of the drain current versus the drain voltage showed that the drain current when using long-term heat treatment is significantly higher than after rapid heat treatment. In this case, for long-term heat treatment, there is a decrease in the channel breakdown voltage only for n-channel transistors and an increase in the drain current in the region of more than 5 V for both n- and p-channel transistors. Such improvements occur by eliminating the formation of polysilicon conglomerates in the aluminum contact, significantly reducing the epitaxial recrystallization of silicon doped with aluminum on the silicon surface, as well as reducing the microrelief of the interface of this contact and reducing the growth in the size of contact windows due to the lateral interaction of aluminum with polysilicon.

Quantitative Optimization of Handheld Probe External Pressure on Dermatological Microvasculature Using Optical Coherence Tomography-Based Angiography.

Optical Coherence Tomography (OCT)-based angiography (OCTA) is a high-resolution, high-speed, and non-invasive imaging method that can provide vascular mapping of subcutaneous tissue up to approximately 2 mm. In dermatology applications of OCTA, handheld probes are always designed with a piece of transparent but solid contact window placed at the end of the probe to directly contact the skin for achieving better focusing between the light source and the tissue, reducing noise caused by minor movements. The pressure between the contact window and the skin is usually uncontrollable, and high external pressure affects the quality of microvascular imaging by compressing the vessels and obstructing the underlying blood flow. Therefore, it is necessary to determine a pressure range to ensure that the vessels can be fully imaged in high-quality images. In this paper, two pressure sensors were added to the existing handheld OCT probe, and the imaging probe was fixed to a metal stand and adjusted vertically to change the pressure between the probe and the tested skin site, a gradient of roughly 4 kPa (with 1-2 kPa error) increase was applied in each experiment, and the impact of pressure to the vessel was calculated. The experiment involved a total of five subjects, three areas of which were scanned (palm, back of the hand, and forearm). The vessel density was calculated to evaluate the impact of external pressure on angiography. In addition, PSNR was calculated to ensure that the quality of different tests was at a similar level. The angiography showed the highest density (about 10%) when the pressure between the contact window on the probe and the test area was between 3 and 5 kPa. As the pressure increased, the vascular density decreased, and the rate of decrease varied in different test areas. After fitting all the data points according to the different sites, the slope of the fitted line, i.e., the rate of decrease in density per unit value of pressure, was found to be 4.05% at the palm site, 6.93% at the back of the hand, and 4.55% at the forearm site. This experiment demonstrates that the pressure between the skin and contact window is a significant parameter that cannot be ignored. It is recommended that in future OCTA data collection processes and probe designs, the impact of pressure on the experiment be considered.

Real-time adaptive scheduling optimization for inter-satellite contact window resources in dynamic satellite networks

Real-time scheduling of contact window resources is a fundamental technology for the future construction of Space–Terrestrial Integrated Networks (STIN). The spatio-temporal dynamics of satellite networks result in continuous variations in satellite relative positions and inter-satellite visibility window resource status. Furthermore, frequent changes in task priority make real-time resource scheduling extremely challenging. Centralized online scheduling methods often lead to a significant amount of waiting time, while distributed online scheduling methods struggle to adapt to the high dynamics of satellite networks. Therefore, the real-time scheduling technology for contact window resources in satellite networks is still in the exploration phase. We propose an inter-satellite online resource allocation method to solve the latency issue caused by the seizure of contact window resources. First, we determine the shortest and maximum flow paths set in the satellite network according to task requirements and construct them as the core network. Then, we comprehensively analyze the supply and demand situation of the task and the core network at a specific moment and verify the reliability of our minimum cost flow-solving method based on the core network. Moreover, we consider factors such as changes in task priority and edge modifications and validate the correctness of our method to update the minimum cost flow at the next moment based on local network changes. Finally, through extensive comparative simulations, we evaluate the absolute advantage of our inter-satellite online scheduling method and validate a significant improvement in task scheduling timeliness.

Joint In-Orbit Computation and Communication for Minimizing Download Time From LEO Satellites

Downloading a large amount of data from a low Earth orbit satellite to a ground station can be challenging due to the limited contact window, dynamic channel quality, solar energy supply, and thermal management without an atmosphere. Considering such dynamics, this paper proposes a joint design of in-orbit computation and communication for download time minimization. We combine the non-convex thermal constraints and energy constraints into unified energy budget constraints with upper bound approximation, and computational efficiency is achieved by decomposing the resulting large-scale problem into a non-convex communication sub-problem, a convex computation sub-problem solvable with interior point method and a master problem that optimizes the energy budget allocation between computation and communication. The communication sub-problem is solved with a generalized-benders-decomposition-based algorithm that decouples downlink scheduling and power allocation based on a closed-form solution of optimal dual variables in the power allocation primal problem. And the master problem is solved with ternary search by proving the minimal download time is quasi-convex with respect to the energy budget allocation between computation and communication. Simulation results demonstrate that the proposed solution effectively reduces the download time, especially under strict energy constraints and severe channel variations.

Passivation of a Conductive System of Integrated Circuits with a Layer of Aluminum Nitride

Passivation of the film conductive system of integrated circuits makes it more reliable by increasing the resistance to electromigration. The problem of manufacturing a passivating layer on the formed current-conducting system of an integrated circuit, obtained in a single technological cycle, including isotropic plasma-chemical etching of an aluminum alloy layer to a depth of 8–12 nm and isotropic plasma-chemical nitriding of the surface of the obtained current-carrying tracks until the aluminum nitride thickness from 10 to 50 nm, is considered. This task makes it possible to form a dielectric film based on silicon dioxide on a silicon substrate with active regions, etch contact windows to active elements of the substrate in the dielectric film, deposit a barrier layer 0.005–0.050 µm thick, and deposit an aluminum alloy film 0.5–2.0 um and much more.

Dynamic Digital Twin and Online Scheduling for Contact Window Resources in Satellite Network

The contact window scheduling technology supports various space mission requirements of the satellite information network. The continuous emergence of new space missions challenges the scarce satellite contact window scheduling. In this paper, We propose a dynamically updated micro-cloud structure based on digital twin and multi-agent system technology. Then, we build an on-satellite autonomous scheduling model based on the micro-cloud structure and design an efficient solution algorithm to solve the maximum revenue problem of inefficient task scheduling caused by the dynamic change of task priority and satellite position over time. Simulation experiments show that the scheme proposed in this paper can significantly improve task scheduling revenue and resource utilization, and have specific enlightening significance for the innovation of satellite task scheduling methods in the future.

Fabrication and Electrical Characterization of High Aspect Ratio Through-Silicon Vias with Polyimide Liner for 3D Integration.

High aspect ratio (HAR) through-silicon vias (TSVs) are in urgent need to achieve smaller keep-out zones (KOZs) and higher integration density for the miniaturization of high-performance three-dimensional (3D) integration of integrated circuits (IC), micro-electro-mechanical systems (MEMS), and other devices. In this study, HAR TSVs with a diameter of 11 μm and an aspect ratio of 10:1 are successfully fabricated in a low-cost process flow. Conformal polyimide (PI) liners are deposited using a vacuum-assisted spin coating technique, and the effects of spin coating time and speed on the deposition results are discussed. Then, continuous Cu seed layers are fabricated by sequential sputtering and ultrasound-assisted electroless plating. Additionally, void-free and seamless Cu conductors are formed by electroplating. Moreover, a semi-additive method is used to fabricate the redistribution layers (RDLs) on the insulating layers of photosensitive PI (PSPI). Notably, a plasma bombardment process is introduced to remove residual PSPI in the contact windows between RDLs and central pillars. Results show that the resistance of a single TSV from a daisy chain of 144 TSVs with density of 2000/mm2 is about 28 mΩ. Additionally, the S-parameters of a single TSV are obtained using L-2L de-embedding technology, and the experimental and simulated results agree well. The proposed low-cost fabrication technologies and the related electrical characterization of PI-TSVs are significant for the application of HAR TSVs in modern heterogeneous integration systems.

A Novel GaN LED Structure With Both P and N Discontinuous Ohmic Contacts and Discontinuous CBL

In this paper, a novel kind of GaN light-emitting diode (LED) with P and N discontinuous ohmic contact electrodes and discontinuous current blocking layer (CBL) is designed and prepared. Multiple contact windows under the N- and P-electrodes formed by etching help realize the discontinuous ohmic contacts with the N-GaN layer and the ITO layer, respectively. Similarly, by etching a plurality of discontinuous openings with the same pitch in the CBL, a discontinuous CBL structure is formed. As compared with traditional structures, the discontinuous ohmic contacts can maximize the number of current paths which allow the carriers to be collected from all four directions, leading to a more uniform current spreading and thermal management. Furthermore, as the contacts are not continuous any longer, some of the otherwise removed materials (such as the active region) lying between the patches are saved. The optoelectronic characteristics, junction temperature, thermal resistance, and infrared thermography measurements are conducted and the current distribution is simulated. The results show that the novel LED structure has better optoelectronic performances and current spreading ability compared to traditional devices. At 150 mA current, the luminous efficiency is 15.2% higher than the traditional LED, the junction temperature is reduced by 4.9%, and the thermal resistance is reduced by 12%.

Electrically Pumped Epitaxially Regrown GaSb‐Based Type‐I Quantum‐Well Surface‐Emitting Lasers with Buried High‐Index‐Contrast Photonic Crystal Layer

Epitaxially regrown electrically pumped photonic crystal surface‐emitting lasers (PCSELs) emitting near 2 and 2.6 μm are designed, fabricated, and characterized. A high‐index‐contrast photonic crystal layer is incorporated into the GaSb‐based laser heterostructure by air‐hole‐retaining epitaxial regrowth. A square lattice of triangular holes is etched in the top waveguide core layer of the incomplete laser heterostructure. The nanopatterned surface is subsequently cleaned and regrown with AlGaAsSb p‐cladding material. Transmission electron microscopy studies demonstrate uniform regrowth over the nanopatterned GaSb surface. The selected regrowth regimes yield a buried 2D array of elongated air‐holes. The diode PCSELs based on moderately etched nanopatterns demonstrate band‐edge lasing near 2 μm up to room temperatures. The cascade diode PCSELs operate near 2.6 μm with minimum threshold current densities of about 500 A cm−2 achieved at 180 K. The devices generate mW level output in narrow divergence beam emitted from the window in substrate contact. The angle‐resolved electroluminescence measurements reveal a four‐sub‐band band structure with an apparent photonic bandgap corresponding to the buried high‐index‐contrast square photonic crystal layer. The PCSELs made of heterostructures supporting two modes in the vertical direction demonstrate two sets of sub‐bands showing anti‐crossing‐like interaction.

(Invited) Characterization of Doping and Activation Processes Using Differential Hall Effect Metrology (DHEM)

As advanced CMOS technology scaling goes beyond 7nm node, contact resistivity becomes an important factor influencing device performance. Approaches to reduce contact resistivity involve advanced doping techniques that yield very high degree of dopant activation at the semiconductor layers comprising the source and drain regions. These approaches include in-situ heavily doped epi layers and ion implantation followed by advanced annealing techniques. Irrespective of the approach used in wafer processing, accurate analysis of dopant activation within the top few nanometers of the surface is critical to understanding the effectiveness of such processes on improving contact resistivity. Similarly, correlation of mobility depth profile to defectivity in the layers helps one to understand how process variables may affect the ultimate electrical properties.Differential Hall Effect Metrology (DHEM) is the only method that can provide mobility and active dopant depth profiles through semiconductor layers at sub-nm resolution. The method employs electrochemical means of reducing the electrically active thickness of a semiconductor film and determining the sheet resistance and mobility of the thinned down layer using Van der Pauw/Hall effect type measurements [1].In this work we characterized an ion implantation/annealing process cycle using DHEM and TEM studies. The sample was a p-type Si wafer ion implanted with P (10keV, 2E15cm-2). After implantation, the wafer was coated with positive photoresist, exposed, and developed in order to define a cross-shaped Van der Pauw structure. After formation of the DHEM test patterns using dry etching, wafer pieces were processed by rapid thermal anneal (RTA) at 750 ºC, 850 ºC, and 950ºC in nitrogen ambient for 30 seconds. After annealing, samples were subjected to a negative photoresist process in order to open contact windows. After the exposure and development, native oxide was removed from the contact windows and metallic contacts were evaporated. Depth profiles of resistivity, mobility, and carrier concentration were measured by DHEM using an ALPro™ 50 electrical profiling tool.Fig. 1 shows the cross-sectional TEM images of the P ion implanted samples after annealing at (a) 750ºC, (b) 850ºC, and (c) 950ºC. As can be seen in Fig 1(a) the end of range (EOR) defects are located at approximately 26-30 nm from the surface in this sample. The 750ºC RTA process did not adequately resolve these defects. However, it is clear from the TEMs that defects at the original location of the a-Si/c-Si interface decreased gradually when the samples were annealed at increasing RTA temperatures (see Fig. 1(b−c)), when crystallinity of the ion implanted top layer also improved.The depth profiles of active carrier concentration after RTA process are given in Fig.2(a). Three regions can be discussed in these depth profiles. Region 1 is within 15nm of the surface, region 2 is at around 20-30 nm depth, and region 3 is at depths at or larger than 40nm. As can be seen in this figure, higher and higher RTA temperatures result in diffusion of P impurities deeper, and dopant activation at region 3 gets higher and higher as the anneal temperature is increased from 750ºC to 950ºC. As for the region 1, we observe a small decrease in carrier concentration values with higher temperature (from about 3.77E+20 #/cm3 to about 2.95E+20 #/cm3) as the overall active dopant profile becomes more uniform due to diffusion.Figure 2(b) shows the mobility depth profiles of the three samples discussed with reference to Fig. 1 and Fig. 2(a). It is obvious from this figure that the mobility profile is relatively flat within the implantation region (<30nm). Notably the mobility value for the RTA 750ºC sample dips at a depth in the range of 25-30 nm, where Fig. 1(a) shows extensive EOR defectivity. Therefore, the correlation with deteriorated mobility at that region is excellent. It is also clear from the mobility data that as the annealing temperature is raised to 850ºC and then to 950ºC this dip in mobility disappears, suggesting reduction in defects through higher temperature annealing. Deeper region (>40nm) mobility reduces with increasing temperatures because of increased carrier scattering mechanisms as more of the dopant is activated deeper at the elevated temperatures.Through this work we have demonstrated how DHEM technique can be utilized to correlate electrical and physical data obtained from samples subjected to doping processes. At the present time we are extending this work to ultra shallow junction structures and these results will be presented at the conference.

Verification of a Fabless Device Model Using TCAD Tools: from Bipolar Transistor Formation to I-V Characteristics Extraction

This paper describes the analysis of processes used in microand nanoelectronic device manufacturing. It also presents an exemplary and novel laboratory exercise in which an epitaxial planar n + pn bipolar transistor with junction isolation is illustrated and analyzed stepbystep. Only seven photolithography steps are used to obtain this bipolar transistor structure: for buried layer formation, for junction transistor isolation and collectors regions formation, for base region formation, for emitter and collector n+ region formation, for contact windows, for first aluminum metallization, and, finally, for passivation. Silvaco TCAD software tools are used to implement all of these manufacturing processes and to simulate the resulting IV characteristics of all presented semiconductor structures. This type of laboratory work provides students with basic knowledge and a consistent understanding of bipolar transistor manufacturing, as well as facilitating theoretical understanding, analysis, and simulation of various semiconductor manufacturing processes without the need for costly and lengthy technological manufacturing experiments. This article also presents the conclusions and other benefits of such laboratory work, as well as possible recommendations for further improvement or expansion.

Hot-electron photocurrent detection of near-infrared light based on ZnO

We demonstrate an unconventional near-infrared photodetector fabricated from a ZnO chip with a metallic subwavelength grating structure as a contact and optical window, which harvests hot electrons generated by plasmonic resonances introduced by incident light. The grating structure has a strong selection of the polarization of incident light, meaning that the detector is naturally polarization-sensitive. In our device, the polarization extinction ratio is as high as 64:1, much higher than that relying on crystal orientations. Since the photoresponse is introduced by plasmonic resonance, a narrow photoresponse spectrum with a linewidth of 32.1 nm at 1.201 μm is obtained. By simply changing the grating period, the spectral position can be tailored freely within the near-infrared region, i.e., wavelength-selective. Such a spectral response is not likely to be realized with conventional semiconductor photodetectors, which depend on the band edge absorption. We propose a modified Fowler's model, which well explains the line shape of photoresponse spectra of such devices.

ОБЕСПЕЧЕНИЕ КАЧЕСТВА ДЕТАЛЕЙ, ИЗГОТОВЛЕННЫХ С ПОМОЩЬЮ АДДИТИВНЫХ ТЕХНОЛОГИЙ

On this account the purpose of this work became quality parameter support of products obtained with the aid of 3D-printing. By the authors there was carried out a series of investigations on samples manufactured on the Ultra 3 3D-printer of the Envision Tec. Company. The samples were manufactured in batches of seven samples in each. Each sample from the batch varied from each other with the growth angle α between the researched surface and a “contact window”, and also the thickness of the layer z. With the aid of the profile meter TR110 there was measured roughness and for a thorough analysis of roughness step dimensions there was used a probe microscope of SolverPro company operating in the mode of atomic-power microscopy. The data analysis helped to draw a conclusion on the nature of roughness formation at prototyping, and digital data obtained were accumulated in a table and with the aid of statistical processing there was deduced an equation of the roughness parameter dependence of the surface Ra upon initial technological parameters of the prototyping process. But further roughness improvement can be achieved with the combined shaping with the aid of additive technologies and further machining carried out on a single platform. Investigation methods: at the heart of the work underlie experimental methods of investigation. The investigations are carried out with the use of modern means of nondestructive control; with the use of methods of probe microscopy and standard methods of roughness measurement with the use of a profile meter. The processing of investigation results is carried out with the use of modern mathematical apparatus. Work novelty: there is defined the nature of roughness formation on the surface of a product manufactured with the aid of additive technologies at technological parameter variation of prototyping.

Research progress on gel polymer electrolytes for lithium-sulfur batteries

Recent progress on gel polymer electrolytes consisting of solid hosts, liquid solutions and fillers with an outstanding performance for lithium-sulfur batteries is reviewed, and the corresponding relationship between different components and cell performance is highlighted. Lithium-sulfur (Li-S) batteries have become a promising candidate for advanced energy storage system owing to low cost and high theoretical specific energy. In the last decade, in pursuit of Li-S batteries with enhanced safety and energy density, the investigation on the electrolytes has leaped form liquid organic electrolytes to solid polymer ones. However, such solid-state Li-S battery system is greatly limited by unfavorable ionic conductivity, poor interfacial contact and narrow electrochemical windows on account of the absence of any liquid components. To address these issues, gel polymer electrolytes (GPEs), the incorporation of liquid electrolytes into solid polymer matrixes, have been newly developed. Although the excellent ionic transport and low interfacial resistance provided by GPEs have prompted numerous researchers to make certain progress on high-performance Li-S coins, a comprehensive review on GPEs for Li-S batteries remains vacant. Herein, this review focuses on recent development and progress on GPEs in view of their physical and chemical properties for the applications in Li-S batteries. Studies on the components including solid hosts, liquid solutions and fillers of GPEs are systematically summarized with particular emphasis on the relationship between components and performance. Finally, current challenges and directional outlook for fabricating GPEs-based Li-S batteries with outstanding performance are outlined.

Early recruiting in NCAA sport: An exploratory study of scarcity effects

ABSTRACT Current sources of information regarding the effects of early recruiting in college athletics, on which recent NCAA bylaw changes were predicated, are grounded in anecdotal accounts of deleterious effects on the psychosocial health of adolescent athletes [e.g. DaSilva, M. (2016, May 17). Straight talk: A special LM roundtable on early recruiting. US Psychological Foundations of AttitudesLacrosse Magazine. http://laxmagazine.com/mag/2016/05/051716_straight_talk_lacrosse_magazine_roundtable_on_early_recruiting.; Popper, N. (2014, January 26). Committing to lay for a College, then Starting the 9th Grade. New York Times. http://www.nytimes.com/2014/01/27/sports/committing-to-play-for-a-college-then-starting-9th-grade.html?_r=0.). Through the lens of scarcity effects [Brock, T. C. (1968). Implications of commodity theory for value change., 1, 243–275. https://doi.org/10.1016/B978-1-4832-3071-9.50016-7], an exploratory study was conducted to examine parents’ perspectives on the effects of an accelerated recruiting timeline on the college choice factors, the decision to accept a verbal scholarship offer, and the psychosocial outcomes of the recruiting process for their child. Interviews (N=12) conducted with parents of female soccer prospective student-athletes who were recruited prior to NCAA permissible contact windows indicated that brand value and program coach were given primacy over academics as college choice factors, and that the fear of losing out on a scholarship and the desire for cognitive closure affected the timeline for accepting a verbal scholarship offer.

Customer Services and Its Efficiency Level of 3rd Party Logistics Companies

This research explores the function of Customer Service (CS) in Third-Party Logistics (3PL) companies and their efficiency levels. Many 3PL companies rely on the performance of its CS department as the windows of contact between external customers and internal customers. Despite the critical function of CS in 3PL companies, less attention is given on the development and progress of the CS area. Poor CS performance leads to miscommunication among internal departments, suppliers and worst its customers. This situation, if prolonged, will give a high toll in operations cost and the company’s reputation in the industry. While companies with excellent CS team retain, more extended customers’ relationship and support derived from reliable services and trust experienced by customers with less additional or unexpected operations cost occurrence. The first objective of this study is to identify the factors influencing the CS efficiency and the second objective determined the level of efficiency of CS in 3PL companies. A thorough archival data were compiled and observed from previous studies conducted in this field. Interviews were conducted with selective respondents from 3PL companies located in Johor Bahru to measure CS efficiency. The findings of this research revealed each companies’ CS team performance and recommended areas for future improvements.

Ohmic Contacts to CVD Diamond with Boron-Doped Delta Layers

Various methods for the formation of ohmic contacts to boron-doped δ layers in CVD-diamond epitaxial structures are investigated. In the first variant, an additional thin heavily doped layer was formed on the diamond surface to which an ohmic contact is formed. Then, the surface p+ layer between the contact pads is etched out; therefore, the current in the structure flows only through a buried δ layer. In the second approach, the doped diamond selectively grows in the contact windows under a metallic mask after preliminary etching of the undoped diamond layer (cap) up to the δ layer. In this case, the heavily doped p+ layer forms an end contact to the δ layer. These two variants differ in terms of the conditions of applicability, the complexity of the manufacturing technology, the value of the contact resistance, and can be used to solve problems in which it is necessary to have a different quality of the contacts, such as the formation of transistor structures or test cells for measuring physical characteristics.

Energy-efficiently collaborative data downloading in optical satellite networks

Optical satellite networks (OSNs) play an important role in space applications since it has some merits such as high data rate and low power. Increasing space applications generate a large amount of data on satellite so that satellites have difficulty in downloading these data to ground station timely under the limited contact window. Thus, we investigate the problem of collaborative data downloading in this paper. The problem lies on how to energy-efficiently offload data by optical inter-satellite links (ISLs) to balance data load and downlink capacity of each satellite so as to improve the performance of data downloading in OSN. Firstly, we develop the Cost Time-evolving Graph (CTEG) to describe optical transmission cost and the time-varying topology of OSN. Secondly, the problem of collaborative data downloading is formulated as Multi-objective Mixed-integer Linear Programming (MOMILP) which is proven to be NP-hard. For reducing computational complexity, we divide the scheduling time into multiple stages and propose the Multi-stage Collaborative Scheduling Algorithm (MCSA) which operates on a slot-by-slot basis. Simulations are conducted in the joint platform and results demonstrate that, compared with CoDld and No-ISLs, the MCSA provides a relatively high data throughput meanwhile drastically reducing energy consumption generated by data offloading.

Measurement of band offsets and shunt resistance in CdTe solar cells through temperature and intensity dependence of open circuit voltage and photoluminescence

Band offsets at the back contact and front window layer in CdTe-based solar cells affect photovoltaic performance and challenge standard characterization methods. By analyzing the temperature and excitation dependence of both open circuit voltage and absolute photoluminescence intensity, we show that the effects band offsets can be separated from the effects of recombination and shunting. Solar cells were grown with MgZnO window layers and compared to cells with CdS window layers containing varying amounts of oxygen. It was demonstrated that band alignment rather than reduced recombination velocity is the reason for the success of MgZnO as a front interface contact. An assortment of thin back contact interlayers were also deposited, and a PbTe interlayer showed some promise as an Ohmic contact to the CdTe, though it appears to induce a photoconductive shunt. Finally, we show that the shunting resistance given by a standard current-voltage curve technique generally does not represent a physically meaningful quantity unless it is well below one kiloOhm square cm.

Омические контакты к эпитаксиальным структурам CVD-алмаза с дельта-слоями бора

Various methods of the formation of ohmic contacts to CVD diamond epitaxial structures with boron doped delta layers (δ-layers) are investigated. In the first approach, an additional thin, heavily doped layer was formed on the surface of the diamond film, to which the ohmic contact was formed. Then, the surface p+-layer between the contact pads was etched out, so the current flow in the structure occurred only through the buried δ-layer. In the second approach, doped diamond was selectively grown in contact windows under the mask of metal after preliminary etching the undoped diamond layer (cap) to the δ-layer. In this case, the heavily doped p+-layer will form a contact to the δ-layer. These approaches are differs by conditions of applicability, the complexity of manufacturing technology, the value of contact resistance. So they can be used to solve tasks in which different quality of contacts is required, such as the formation of transistor structures or test cells for measuring electrophysical characteristics.