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Structural and electrical properties of Pd/p-GaN contacts for GaN-based laser diodes
摘要： In this paper, the properties of Pd-based p-contacts on GaN-based laser diodes are discussed. Pd is often the metal of choice for ohmic contacts on p-GaN. However, for Pd/p-GaN ohmic contacts, nanovoids observed at the metal/semiconductor interface can have a negative impact on reliability and also reproducibility. The authors present a thorough analysis of the microstructure of the Pd/p-GaN interface by x-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). STEM data show that the microvoids at the p-GaN/Pd interface form during rapid thermal annealing. A combination of the following effects is suggested to support the void formation: (1) the differences in thermal expansion coefficients of the materials; (2) excess matrix or impurity atoms in the semiconductor, at the interface, and in the metals, which are released as gases; and (3) the strong antisurfactant effect of Pd on Ga-rich p-GaN surfaces. A slow temperature ramp during contact annealing reduces the formation of voids likely by suppressing the accumulation of gases at the interface. XPS data show that the Ga/N ratio can be reduced by suitable cleaning of the p-GaN surface, which enhances Pd adhesion. As a result, the quality of the contact system is improved by the systematic optimization of the surface cleanliness as well as the annealing parameters, leading to void-free and clean Pd/p-GaN interfaces. The specific contact resistance, extracted from linear transmission line method measurements, is reduced by an order of magnitude to 2 × 10?3 Ω cm2 at 1 mA for the same epitaxial layer stack.
关键词： Pd/p-GaN contacts,STEM,nanovoids,ohmic contacts,rapid thermal annealing,XPS,GaN-based laser diodes
更新于2025-09-23 15:21:01
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Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods
摘要： Polarity-controlled growth of ZnO by chemical bath deposition provides a method for controlling the crystal orientation of vertical arrays of nanorods. The ability to define the morphology and structure of the nanorods is essential to maximising the performance of optical and electrical devices such as piezoelectric nanogenerators; however, well-defined Schottky contacts to the polar facets of the structures have yet to be explored. In this work, we demonstrate a process to fabricate metal-semiconductor-metal device structures from vertical arrays with Au contacts on the uppermost polar facets of the nanorods and show the O-polar nanorods (~0.44 eV) have a greater effective barrier height than the Zn-polar nanorods (~0.37 eV). Oxygen plasma treatment is shown by Cathodoluminescence (CL) spectroscopy to reduce mid-gap defects associated with radiative emissions that improves the Schottky contacts from weakly-rectifying to strongly-rectifying. Interestingly, the plasma treatment was shown to have a much greater effect in reducing the number of carriers in O-polar nanorods through quenching of the donor-type substitutional hydrogen on oxygen sites (HO) when compared to the zinc vacancy related hydrogen defect complexes (VZn, Hn) in Zn-polar nanorods that evolve to lower coordinated complexes. The effect on HO in the O-polar nanorods coincided with a large reduction in the visible range defects producing a lower conductivity and creating the larger effective barrier heights. This combination can allow radiative losses and charge leakage to be controlled enhancing devices such as dynamic photodetectors, strain sensors, and LEDs while showing the O-polar nanorods can outperform Zn-polar nanorods in such applications.
关键词： ZnO,Cathodoluminescence,Electrical Transport,Polarity,Schottky Contacts,Nanorods,Defects
更新于2025-09-23 15:21:01
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Switchable Multi-Color Solution-Processed QD-laser
摘要： In this paper, for the first time, the switchable two-color quantum dot laser has been realized considering solution process technology, which has both simultaneous and lonely lasing capability exploiting selective energy contacts. furthermore, both channels can be modulated independently, which is a significant feature in high-speed data transmission. To this end, utilizing superimposed quantum dots with various radii in the active layer provides the different emission wavelengths. In order to achieve the different sizes of QDs, solution process technology has been used as a cost-effectiveness and fabrication ease method. Moreover, at the introduced structure to accomplish the idea, the quantum wells are used as separate selective energy contacts to control the lasing channels at the desired wavelength. It makes the prominent device have simultaneous lasing at different emission wavelengths or be able to lase just at one wavelength. the performance of the proposed device has been modeled based on developed rate equation by assuming inhomogeneous broadening of energy levels as a consequence of the size distribution of quantum dots and considering tunnel injection of carriers into the quantum dots via selective energy contacts. Based on simulation results, the simultaneous lasing in both or at one of two wavelengths 1.31 μm and 1.55 μm has been realized by the superimposition of two different sizes of InGaAs quantum dots in a single cavity and accomplishment of selective energy contacts. Besides, controlling the quantum dot coverage leads to managing the output power and modulation response at the desired wavelengths. By offering this idea, one more step is actually taken to approach the switchable QD-laser by the simple solution process method.
关键词： solution process technology,high-speed data transmission,multi-wavelength lasing,quantum dot laser,selective energy contacts
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - On the impact of the metal work function on the recombination in passivating contacts using quasi-steady-state photoluminescence
摘要： Understanding the impact of metal contacts on the recombination within a passivated silicon wafer is crucial for the optimization of various photovoltaic devices such as passivating-contact-based solar cells. To investigate the effect of the metal work function, a selection of metals is applied to aluminum-oxide-passivated n-type crystalline silicon wafers. The saturation current density of the metalized contact (J0m) is determined using the quasi-steady-state photoluminescence method and used as a figure of merit to quantify the effect. We find that J0m increases with the metal work function and that this effect is modulated with the passivation layer thickness. It is more pronounced for thinner passivation layers, which can be attributed to a significant change in the populations of electrons and holes near the silicon surface induced by the metal. Meanwhile thicker layers prevent the charge transfer between the silicon and metal more efficiently leading to insignificant changes in J0m. Based on these findings, we suggest a suitable metal work function range to optimize contact recombination in silicon-based solar cells.
关键词： passivating contacts,surface recombination,saturation current density,quasi-steady-state photoluminescence,work function,Effective lifetime,silicon solar cells
更新于2025-09-23 15:21:01
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In Situ Study of Sputtering Nanometer-Thick Gold Films onto 100 Nanometer-Thick Spiro-OMeTAD Films: Implications for Perovskite Solar Cells
摘要： The performance of many perovskite solar cells is closely related to the spiro-OMeTAD/gold interface since gold is used as top contacts, which renders the detailed understanding of the interface formation very important. In this work, sputter deposition as an industry-relevant, high-rate, large-scale and well-controllable deposition technique is used to prepare gold electrodes on top of a 100 nm thick spiro-OMeTAD film. In situ grazing incidence small angle X-ray scattering (GISAXS) is used to study the nanostructure-growth kinetics of the gold contact on top of the spiro-OMeTAD film during the sputter process. The results show that the gold grows in nanoscale clusters, which then coalesce into a complete yet still nanogranular layer forming the top contact with a thickness of 90 nm. Based on simulations of the 2D GISAXS patterns additional information about the shape of the nanosized gold cluster is gained at the different cluster growth stages. Furthermore, the diffusion of gold into the spiro-OMeTAD film occurs during the sputter process as verified with X-ray reflectivity. In a depth of 3.5 nm below the gold contact the gold doping level of the spiro-OMeTAD film is 6.3 % irrespective of the final gold contact thickness. Thus, the interface between the spiro-OMeTAD film and the Au contact is not sharp as commonly sketched as well as the contact is grainy, which will be both of importance for the performance of device such as perovskite solar cells.
关键词： gold contacts,spiro-OMeTAD film,sputter deposition,in situ GISAXS,growth kinetics
更新于2025-09-23 15:21:01
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Challenges and opportunities for efficiency boost of next generation Cu(In,Ga)Se <sub/>2</sub> solar cells: prospect for a paradigm shift
摘要： Cu(In,Ga)Se2 photovoltaic technology has notably progressed over the past years. Power conversion efficiencies above 23% were reached in spite of the absorber polycrystalline nature. Although efficiencies are still far from the practical limits, the material quality is approaching that of III-V compounds that yield the most efficient solar cells. High carrier lifetime, low open circuit voltage deficit and external radiative efficiency in single-digit percentage range, suggest the next efficiency boost may arise from the implementation of alternative device architectures. In this perspective paper, we describe the current challenges and pathways to enhance the power conversion efficiency of Cu(In,Ga)Se2 solar cells. Specifically, we suggest the use of non-graded absorbers, integration of charge selective contacts and maximization of photon recycling. We examine these concepts by a semi-empirical device modelling approach, and show that these strategies can lead to efficiencies of 29% under the AM1.5 global spectrum. An analysis whether or not current state-of-the-art Cu(In,Ga)Se2 solar cells already benefit from photon recycling is also presented.
关键词： Cu(In,Ga)Se2,charge selective contacts,photon recycling,power conversion efficiency,solar cells
更新于2025-09-23 15:21:01
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Laser firing in silicon heterojunction interdigitated back contact architecture for low contact resistance
摘要： This work reports a laser firing technique applied to completed silicon heterojunction interdigitated back contact solar cells in order to lower contact resistance. Previously, the implementation of a-Si:H(i) at the electron contact of polycrystalline silicon solar cells on glass substrates led to an increase in series resistance. The cell architecture with the current record efficiency of 14.2% (with illumination through glass) utilizes only an a-Si:H(nt) layer (cid:0) 2 of short circuit current density is lost due to electrical shading under the electron contact and 2–2.9 mA cm [1,2]. The goal of implementing an a-Si:H(i) layer and laser firing at this contact is to achieve low contact resistance at fired spots while preserving a-Si:H(i) passivation in unfired regions. After the laser firing, VOC was (cid:0) 2 loss in JSC. In the best retained, while up to 14% absolute increase in FF was obtained with a mere 0.2 mA cm (cid:0) 2 loss in JSC. Two laser sources were used to first performing cell, a 72.1% FF was achieved with a 0.7 mA cm ablate a part of the silver contact metal, and then to laser fire through the Si(n)/a-Si:H(i/nt)/ITO/Ag contact. (cid:0) 2 (355 nm, picosecond pulse duration) and The optimal laser fluence was found to be 1.1–0.5 J cm (cid:0) 2 (532 nm, nanosecond pulse duration), respectively. The upper limit on specific contact resistance 4.4–5.2 J cm in the laser fired spots was calculated to be 38 ? 20 mΩcm2 as a conservative estimate.
关键词： Liquid phase crystallized silicon,Passivation,Interdigitated back contact,Foreign substrates,Laser fired contacts,Silicon heterojunction
更新于2025-09-23 15:19:57
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Doped hydrogenated nanocrystalline silicon oxide layers for higha??efficiency ca??Si heterojunction solar cells
摘要： Hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) layers exhibit promising optoelectrical properties for carrier-selective-contacts in silicon heterojunction (SHJ) solar cells. However, achieving high conductivity while preserving crystalline silicon (c-Si) passivation quality is technologically challenging for growing thin layers (less than 20 nm) on the intrinsic hydrogenated amorphous silicon ((i)a-Si:H) layer. Here, we present an evaluation of different strategies to improve optoelectrical parameters of SHJ contact stacks founded on highly transparent nc-SiOx:H layers. Using plasma-enhanced chemical vapor deposition, we firstly investigate the evolution of optoelectrical parameters by varying the main deposition conditions to achieve layers with refractive index below 2.2 and dark conductivity above 1.00 S/cm. Afterwards, we assess the electrical properties with the application of different surface treatments before and after doped layer deposition. Noticeably, we drastically improve the dark conductivity from 0.79 to 2.03 S/cm and 0.02 to 0.07 S/cm for n- and p-contact, respectively. We observe that interface treatments after (i)a-Si:H deposition not only induce prompt nucleation of nanocrystals but also improve c-Si passivation quality. Accordingly, we demonstrate fill factor improvement of 13.5%abs from 65.6% to 79.1% in front/back-contacted solar cells. We achieve conversion efficiency of 21.8% and 22.0% for front and rear junction configurations, respectively. The optical effectiveness of contact stacks based on nc-SiOx:H is demonstrated by averagely 1.5-mA/cm2 higher short-circuit current density thus nearly 1%abs higher cell efficiency as compared with the (n)a-Si:H.
关键词： silicon heterojunction (SHJ),carrier-selective-contacts (CSCs),interface treatments,optoelectrical properties,hydrogenated nanocrystalline silicon oxide (nc-SiOx:H)
更新于2025-09-23 15:19:57
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Passivating contacts and tandem concepts: Approaches for the highest silicon-based solar cell efficiencies
摘要： The efficiency of photovoltaic energy conversion is a decisive factor for low-cost electricity from renewable energies. In recent years, the efficiency of crystalline silicon solar cells in mass production has increased annually by about 0.5–0.6%abs per year. In order to maintain this development speed, new technologies must be developed and transferred to industrial production. After the transition from full area Al back surface field cells to passivated emitter and rear contact cells, passivating contacts are an important step to get as close as possible to the efficiency limit of single junction Si solar cells. The theoretical background and the two prominent technologies for passivating contacts are presented and discussed. After implementing passivating contacts, the fundamental limit of single junction Si solar cells of 29.4% is in reach. Multi-junction solar cells are the most promising option to achieve efficiencies greater than 30%. Tandem technologies based on crystalline silicon as bottom cells have the advantage that they are based on a mature technology established on a gigawatt scale and can partially use the existing production capacity. In addition, silicon has an ideal bandgap for the lower subcell of a tandem solar cell. The two most promising material candidates for the top cell, i.e., III/V and perovskites, will be discussed. The presented technology routes show that silicon is able to maintain its outstanding position in photovoltaics in the coming years.
关键词： perovskites,multi-junction solar cells,III/V,photovoltaic energy conversion,passivating contacts,tandem technologies,crystalline silicon solar cells
更新于2025-09-23 15:19:57
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Supramolecular Design of Donor-Acceptor Complexes via Heteroatom Replacement towards Structure and Electrical Transporting Property Tailoring
摘要： A feasible strategy relies on using heteroatom replacement which is namely chemical modification to the organic compound. Here we present this design concept for donor-acceptor complexes, which involves introducing nitrogen atoms to the middle ring of donor molecules to promote short contacts and reduce steric effect of the mixed framework. These nitrogen modified complexes are able to possess shorter molecular distance besides the mixed stacking pathway, enlarged π–π interactions or even a scarce 1:2.5 molar ratio through extra acceptor insertion. As a result, the unique 1:2 complex with nitrogen atoms on the different sides demonstrated stable electron field-effect mobility performance, while the binary system with no nitrogen replacement or N atoms on the identical side displayed poor ambipolar properties. These results confirmed that the heteroatom replacement is a powerful molecular design tool to fine tune the molecular packing of organic donor-acceptor complexes and their corresponding electronic properties.
关键词： Theoretical Calculation,Electron Transport,Heteroatom Replacement,Supramolecular Design,Short Contacts,Stoichiometry Varying
更新于2025-09-23 15:19:57