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Hybrid chemical bath deposition-CdS/sputter-Zn(O,S) alternative buffer for Cu <sub/>2</sub> ZnSn(S,Se) <sub/>4</sub> based solar cells
摘要： To replace the conventionally used CdS buffers in Cu2ZnSn(S,Se)4 (CZTSSe) based thin-film solar cells, sputtered Zn(O,S) buffer layers have been investigated. Zn(O,S) layers with three different [O]/([O] + [S]) ratios (0.4, 0.7, and 0.8)—and a combination of Zn(O,S) and CdS (“hybrid buffer layer”) were studied. In comparison to the CdS reference, the external quantum efficiency (EQE) of the Zn(O,S)-buffered devices increases in the short- and long-wavelength regions of the spectrum. However, the average EQE ranges below that of the CdS reference, and the devices show a low open-circuit voltage (VOC). By adding a very thin CdS layer (5 nm) between the absorber and the Zn(O,S) buffer, the VOC loss is completely avoided. Using thicker intermediate CdS layers result in a further device improvement, with VOC values above those of the CdS reference. X-ray photoelectron spectroscopy (XPS) measurements suggest that the thin CdS layer prevents damage to the absorber surface during the sputter deposition of the Zn(O,S) buffer. With the hybrid buffer configuration, a record VOC deficit, i.e., a minimum difference between bandgap energy Eg (divided by the elementary charge q) and VOC (Eg/q – VOC) of 519 mV could be obtained, i.e., the lowest value reported for kesterite solar cells to date. Thus, the hybrid buffer configuration is a promising approach to overcome one of the main bottlenecks of kesterite-based solar cells, while simultaneously also reducing the amount of cadmium needed in the device.
关键词： VOC deficit,Cu2ZnSn(S,Se)4,CdS,hybrid buffer layer,open-circuit voltage,X-ray photoelectron spectroscopy,thin-film solar cells,Zn(O,S) buffer layers,external quantum efficiency
更新于2025-09-23 15:19:57
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Growth of Ag(1?1?1) on Si(1?1?1) with nearly flat band and abrupt interface
摘要： Growth of Ag films of up to 30 nm thickness on Si(1 1 1) 7 × 7 at room temperature is investigated by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). LEED revealed the coexistence of Ag and Si spots starting with 1 monolayer (ML) of Ag deposited. The Ag lattice constant, starting with 25 ML, is slightly higher than for bulk Ag and increase linearly with Ag thickness, reaching about 4.2 nm for the thickest films. The average terrace widths detected from LEED spot profile analysis are about 30 nm for clean Si(1 1 1) 7 × 7 and about 5.5 nm for the thickest Ag(1 1 1) film, in agreement with STM observations. The intensity variation of core levels analyzed by XPS is taken into account by a model assuming the initial formation of Ag islands with linear variation of coverage vs. the amount of Ag deposited, followed by growth in a quasi layer-by-layer mode. The interface barrier is in the range of 0.4 eV, lower than all values reported previously. Ag deposited on Si(1 1 1) 7 × 7 at room temperature provides flat Ag(1 1 1) for synthesis of 2D materials, and may be used for low barrier Schottky diodes.
关键词： Scanning tunneling microscopy,Low energy electron diffraction,X-ray photoelectron spectroscopy,Ag/Si(1 1 1),Molecular beam epitaxy,Surface barrier height
更新于2025-09-23 15:19:57
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Studying the influence of deposition temperature and nitrogen contents on the structural, optical, and electrical properties of N-doped SnO2 films prepared by direct current magnetron sputtering
摘要： This report focuses on studying and investigating in detail the structural, electrical, and optical properties of p-type N-doped SnO2 (NTO) versus the deposition temperature and nitrogen content. P-type transparent conductive NTO films were deposited on quartz glass substrates using a direct current (DC) magnetron sputtering method. The substitution of oxygen by nitrogen in the SnO2 host lattice was verified using measurements such as X-ray photoelectron spectroscopy. The position of the N3? defect state in the band gap was determined using photoluminescence and ultra-violet-visible spectroscopy measurements. The data for the (110) to (101) rutile lattice planes changed, and the rutile (plane (101)) to cubic (plane (111)) SnO2 phase transition indicated the substitution of oxygen by nitrogen in the SnO2 host lattice. The best p-type conductive properties achieved were 8 × 10?2 Ω cm, 1.36 × 1019 cm?3, and 6.75 cm2 V?1 s?1 for the resistivity, hole concentration, and hole mobility, respectively, for film deposited at the optimum substrate temperature of 300 °C in a gas mixture of Ar and 50% N2.
关键词： deposition temperature,nitrogen content,p-type N-doped SnO2 thin film,X-ray photoelectron spectroscopy,DC magnetron sputtering,X-ray diffraction
更新于2025-09-19 17:15:36
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Mechanical stress dependence of the Fermi level pinning on an oxidized silicon surface
摘要： A combination of micro-Raman spectroscopy and micro-XPS (X-ray photo-electron spectroscopy) mapping on statically deflected p-type silicon cantilevers is used to study the mechanical stress dependence of the Fermi level pinning at an oxidized silicon (001) surface. With uniaxial compressive and tensile stress applied parallel to the ?110? crystal direction, the observations are relevant to the electronic properties of strain-silicon nano-devices with large surface-to-volume ratios such as nanowires and nanomembranes. The surface Fermi level pinning is found to be even in applied stress, a fact that may be related to the symmetry of the Pb0 silicon/oxide interface defects. For stresses up to 240 MPa, an increase in the pinning energy of 0.16 meV/MPa is observed for compressive stress, while for tensile stress it increases by 0.11 meV/MPa. Using the bulk, valence band deformation potentials the reduction in surface band bending in compression (0.09 meV/MPa) and in tension (0.13 meV/MPa) can be estimated.
关键词： Mechanical stress,Raman spectroscopy,X-ray photoelectron spectroscopy,Surface Fermi level pinning,Silicon,Interface defect
更新于2025-09-19 17:15:36
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On the Adherence of Chemically Deposited CdS Films to Common Inorganic Substrates: Effect of Cd <sup>2+</sup> Concentration in Solution, Substrate Surface Chemistry, and Reaction Temperature
摘要： The bad adherence to the substrate of chemical-solution-deposited chalcogenide films in alkaline solution is a current technological problem. However, this issue is belittled since is commonly solved by employing pre-sensitized substrates or by empirically changing the deposition parameters until 'finding' the 'proper' chemical formulation. For these reasons, the issue of the adherence has not been previously studied. The present research aims to properly discuss the issue of adherence by taking as example CdS. As a substrate, we used float glass sheets to take advantage of this interesting flat glass (different tin content). It was found that both the surface chemical composition of the substrate and the concentration of Cd2+ in the reaction solution play important roles in the adherence of the CdS thin films; an important effect of temperature was also found. The results were also consistent for indium tin oxide and silicon wafer surfaces. We propose a general surface reaction scheme which considers both the surface reactive sites and the hidroxo–cadmium–thiourea complexes of the reaction solution, as well as the formation of a surface intermediate entity which dissociates into a CdS molecule bonded to the surface and byproducts. The adherence depends on the quantity of surface intermediate entities formed, and therefore, the conditions that promote their formation contribute to the adherence: high reagent concentration, high-reactive surface sites, and low reaction temperature.
关键词： Float Glass,X-Ray Photoelectron Spectroscopy (XPS),Chemical Bath Deposition,Film Adherence,Tin Oxide
更新于2025-09-19 17:15:36
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Epitaxial growth and determination of the band alignment for NixMg1-xO/MgO interface by laser molecular beam epitaxy
摘要： By laser molecular beam epitaxy, single crystalline NixMg1-xO films have been successfully synthesized on MgO(100) surface. The in situ reflection high-energy electron diffraction patterns show that the induced O2 background gas with at least 1.0 × 10?3 Pa is necessary to the epitaxial growth of NixMg1-xO films. The X-ray diffraction patterns reveal the single-phase growth along (200) direction. The energy band alignment at the interface is investigated by employing in situ X-ray photoelectron spectroscopy. The valence band offsets are determined to be from 1.47 eV to 1.50 eV with the decrease of Ni content (0.39 / 0.35). Furthermore, the work function is evaluated by using in situ ultraviolet photoemission spectroscopy, indicating the values from 4.33 eV to 4.64 eV. This study provides a promising guidance for the solar-blind device design and fabrication.
关键词： Work function,X-ray photoelectron spectroscopy,Band alignment,Ultraviolet photoemission spectroscopy,Laser molecular beam epitaxy
更新于2025-09-19 17:13:59
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Indium sulfide based metal-semiconductor-metal ultraviolet-visible photodetector
摘要： In recent years, the photodetectors gained much attention due to their wide range of applications in industry, military, space and biological fields. In this work, the metal-semiconductor-metal (MSM) photodetector was fabricated using In2S3 thin films with Al interdigitated electrodes. The In2S3 thin films were prepared by co-evaporation technique with various thicknesses in the range 130–700 nm at a constant substrate temperature of 350 ?C. The structural, morphological, compositional, optical and electrical properties of In2S3 thin films were studied as a function of thickness. The energy band gap of films is found to be in the range 2.53–2.71 eV. I–V characteristics and photo response of photodetectors were recorded under UV and visible light illumination. The parameters of a photodetector such as photo sensitivity, responsivity and detectivity were calculated. The observed photo responsivity increases with increase of film thickness. The photo response of all photodetectors confirmed the stable and reproducible characteristics such as photo sensitivity, responsivity and detectivity.
关键词： Williamson-Hall plot,Co-evaporation,X-ray photoelectron spectroscopy,Ultraviolet-visible photodetector,Indium sulfide thin films
更新于2025-09-19 17:13:59
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Enhanced thermal stability of InP quantum dots coated with Al-doped ZnS shell
摘要： Colloidal InP quantum dots (QDs) have attracted a surge of interest as environmentally friendly light-emitters in downconversion liquid crystal displays and light-emitting diodes (LEDs). A ZnS shell on InP-based core QDs has helped achieve high photoluminescence (PL) quantum yield (QY) and stability. Yet, due to the difficulty in the growth of a thick ZnS shell without crystalline defects, InP-based core/shell QDs show inferior stability against QY drop compared to Cd chalcogenide precedents, e.g., CdSe/CdS core/thick-shell QDs. In this work, we demonstrate the synthesis of InP-based core/shell QDs coated with an Al-doped ZnS outer shell. QDs with an Al-doped shell exhibit remarkable improvement in thermal and air stability even when the shell thickness is below 2 nm, while the absorption and PL spectra, size, and crystal structure are nearly the same as the case of QDs with a pristine ZnS shell. X-ray photoelectron spectroscopy reveals that Al3+ in Al-doped QDs forms an Al-oxide layer at elevated temperature under ambient atmosphere. The as-formed Al-oxide layer blocks the access of external oxidative species penetrating into QDs and prevents QDs from oxidative degradation. We also trace the chemical pathway of the incorporation of Al3+ into ZnS lattice during the shell growth. Furthermore, we fabricate QD-LEDs using Al-doped and undoped QDs and compare the optoelectronic characteristics and stability.
关键词： quantum yield,QD-LEDs,photoluminescence,Al-doped ZnS shell,X-ray photoelectron spectroscopy,InP quantum dots,thermal stability
更新于2025-09-19 17:13:59
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Band-energy estimation on silicon cap annealed 4H-SiC surface using hard X-ray photoelectron spectroscopy
摘要： Silicon-cap annealing (SiCA) emerged as a promising silicidation-less ohmic contact formation method that can solve the crucial reliability limitation of ohmic contacts formed with metals; this limitation was due to carbon aggregation introduced during silicidation annealing. However, no previous study for a complete understanding of SiCA effects on the metal/SiC exists. In this study, the band-energy state of silicidation-less ohmic contacts formed by SiCA-SiC is directly estimated using hard X-ray photoelectron spectroscopy (HAXPES). The results show that Si-dot formation on the SiC surface reduces the contacts resistivity, and ohmic contact behavior is still observed even after Si-dot removal. A peak position analysis of Si 1 s orbit using HAXPES shows a clear increase in the band energy under various SiC surface conditions. Particularly, the Al/SiCA-SiC sample shows a peak shift of 0.765 eV. This strong potential barrier lowering the derived formation of the thin-depletion layer and low potential barrier on Al/SiCA-SiC junction. Moreover, the observations made using HAXPES, and transmission electron microscopy, suggest that the modification of the outer-most surface layer plays an essential role in the ohmic contact formation. These results provide insights on the ohmic contact formation mechanism for wide-band-gap semiconductor materials.
关键词： 4H-SiC,silicidation-less ohmic contact,Ohmic contacts,silicon-cap annealing,Hard X-ray photoelectron spectroscopy
更新于2025-09-19 17:13:59
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Study of the phase composition and tribological properties of carbon tool steels after laser surface hardening by quasi - CW fiber laser
摘要： The paper contains the investigation results on the structure and phase composition of the laser radiation area (LRA) of the U8 and U10 steels over its entire thickness. In the present study, the laser surface hardening of both U8 (ASTM - W1-7) and U10 (ASTM - W1-9) steels in the air was performed by exploiting a quasi - CW fiber laser with a 130 W power and 3 mm/s processing speed. The phase composition of the oxide layer formed as a result of laser treatment (LT) in air, as well as the structure of the oxide-metal interface on the surface of U8 (ASTM–W1-7) and U10 (ASTM–W1-9) carbon tool steels were studied by X-ray photoelectron spectroscopy (XPS). It was established that the thickness of the completely oxidized surface layers for U8 and U10 steels is 38.7 nm and 99 nm, respectively. The composition of the oxides of the steel surface after LT was determined. The presence of a wüstite-based film on U8 steel evidences the low wear properties of the LRA surface, while the thicker oxide layer of the modified U10 steel which contains Fe2O3 and Fe3O4 oxides with better strength properties, on the contrary, provides U10 steel surface with higher wear resistance. It was found that the wear rate of U10 steel modified surface decreases by more than two times, while the given value for U8 steel reduces no more than 17%. The paper reports the metallographic examination of the LRA structure. It was shown that the wear-resistant structural components that appeared after laser treatment lead to an increase in the deformation properties of steels. The maximum microhardness value of the LRA is 710 HV0.1 for U8 steel and 750 HV0.1for U10 steel.
关键词： Laser radiation,Oxidized surface layers,X-ray photoelectron spectroscopy,Phase composition,Surface finishing treatment,Elemental composition
更新于2025-09-19 17:13:59