Active Layer Of Device Research Articles

Origin of layered perovskite device efficiencies revealed by multidimensional time-of-flight spectroscopy.

Mixtures of layered perovskite quantum wells with different sizes form prototypical light-harvesting antenna structures in solution-processed films. Gradients in the bandgaps and energy levels are established by concentrating the smallest and largest quantum wells near opposing electrodes in photovoltaic devices. Whereas short-range energy and charge carrier funneling behaviors have been observed in layered perovskites, our recent work suggests that such light-harvesting processes do not assist long-range charge transport due to carrier trapping at interfaces between quantum wells and interstitial organic spacer molecules. Here, we apply a two-pulse time-of-flight technique to a family of layered perovskite systems to explore the effects that interstitial organic molecules have on charge carrier dynamics. In these experiments, the first laser pulse initiates carrier drift within the active layer of a photovoltaic device, whereas the second pulse probes the transient concentrations of photoexcited carriers as they approach the electrodes. The instantaneous drift velocities determined with this method suggest that the rates of trap-induced carrier deceleration increase with the concentrations of organic spacer cations. Overall, our experimental results and model calculations suggest that the layered perovskite device efficiencies primarily reflect the dynamics of carrier trapping at interfaces between quantum wells and interstitial organic phases.

Analysis of the thermal stability and optical properties of KBiFe2O5perovskite obtained by a polymeric precursor method

AbstractThe solar cells are the most prominent devices to generate energy from sunlight, however, one of the main factors limiting the efficiency of photovoltaic conversion is the recombination of charge carriers in their active layer, which is generated by the inhomogeneity of the material that constitutes this layer. KBiFe2O5is a perovskite with a high potential to be applied in the active layer of photovoltaic devices, however, it suffers from poor homogeneity during its synthesis, which is caused by the volatilization of K and Bi of its composition and, consequently, leads to the formation of secondary phases, which can sequester the charge carriers and decrease the efficiency of photovoltaic conversion. Thus, our objective is to evaluate the homogeneity of the powders obtained by the polymeric precursor method, its thermal stability until the formation of secondary phases, and the optical properties. With elemental mapping, it was possible to verify that the powder obtained was highly homogeneous and the band gap of 1.74 eV is within the optimal range for applications involving sunlight. Thus, it was possible to verify that this synthesis method generates highly homogeneous powders and at the temperatures employed does not undergo volatilization of K and Bi.

Procedure Optimization for Organic Ambipolar Transistor: Laterally Aligned Micro n‐/p‐Channels via Dry Soft‐Lithographic Process

AbstractIn spite of the large potential of ambipolar transistors constituted of laterally aligned unipolar n‐/p‐channel semiconductors, it is hard to secure the full electrical performance of each semiconductor channel by the risk of intermixing which leads to low crystallinity. Here, a novel fabrication process of patterned taping is proposed which ensures the formation of sharp interface and thus preserving the original performance of individual channels—laterally aligned micro n‐/p‐channels via all‐dry soft‐lithographic process. Different from other bi‐component active layer devices, such as vertically stacked n‐/p‐bilayer and n‐/p‐blend film, laterally aligned n‐/p‐channel of this work secures clear ambipolarity because both the n‐/p‐channels are directly laid over a common gate dielectric surface. Essentially, laterally aligned n‐/p‐channels constructed by patterned taping are free from lateral channel mixing or broadening effect different from other processes such as wet‐processing and fine metal mask (FMM) patterning. In this work, a novel patterned taping method of laterally aligned n‐/p‐channel transistors and also their optimized transistor performances compared with other bi‐component devices using the same set of n‐ and p‐type semiconductor materials is demonstrated.

Disorder‐Induced Dispersive Magneto‐Electroluminescence of Blue Emitters in Organic Light Emitting Diodes

AbstractDisorder‐induced inhomogeneity in blue‐fluorescent‐based organic light‐emitting diodes (OLEDs) based on mixtures of host and guest molecules is studied using magneto‐electroluminescence, MEL(B), response based on the so called “Δg mechanism”, where Δg is the difference in the Landé g‐factor of electrons and holes. The disorder in the organic active layer is manifested by a unique non‐Lorentzian MEL(B) response that is analyzed using a distribution of spin lifetimes for the injected electron–hole pairs that is determined by a dispersive parameter, α (<1). The carriers’ inhomogeneous response also influences the free carrier absorption spectrum, which shows characteristic properties described by a dispersive parameter β (<1). From the measured MEL(B) response at various injection conditions it is found that α is robust at increasing current density showing that the inhomogeneity is governed by intrinsic disorder in the device active layer. Also the obtained increase in α at low temperature indicates that the organic layer becomes more ordered, where longer‐lived electron–hole spin pairs are formed.

High-Performance Flexible InAs Thin-Film Photodetector Arrays with Heteroepitaxial Growth Using an Abruptly Graded InxAl1-xAs Buffer.

Current infrared thermal image sensors are mainly based on planar firm substrates, but the rigid form factor appears to restrain the versatility of their applications. For wearable health monitoring and implanted biomedical sensing, transfer of active device layers onto a flexible substrate is required while controlling the high-quality crystalline interface. Here, we demonstrate high-detectivity flexible InAs thin-film mid-infrared photodetector arrays through high-yield wafer bonding and a heteroepitaxial lift-off process. An abruptly graded InxAl1-xAs (0.5 < x < 1) buffer was found to drastically improve the lift-off interface morphology and reduce the threading dislocation density twice, compared to the conventional linear grading method. Also, our flexible InAs photodetectors showed excellent optical performance with high mechanical robustness, a peak room-temperature specific detectivity of 1.21 × 109 cm-Hz1/2/W at 3.4 μm, and excellent device reliability. This flexible InAs photodetector enabled by the heteroepitaxial lift-off method shows promise for next-generation thermal image sensors.

A potential dual-functional thermoelectric and electroelectric polymer composite

Doping alters the electronic properties of the host semiconducting polymer and may enable tunable devices with temperature sensing and environmental heating/cooling control system applications. We present a doped composite consisting of the p-type semiconducting polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) and a thermoelectric electron acceptor, iodine, as the active layer of a field-effect device, where temperature modulates the current-voltage characteristics and on-off ratios, and gate voltage modulates the thermoelectric properties of the active layer, called dual-functionality. A small amount of iodine doping improved FET output by a factor of 10 as well as thermoelectric power factor by a factor of 3. Those gains are primarily attributed to thermoelectric doping induced charge-carrier density increases.

Growth design for high quality AlxGa(1−x)N layer with high AlN-fraction on Si (1 1 1) substrate by MOCVD

The constraints on increasing the AlN content in active AlGaN device layers on Si substrates for AlGaN-channel HEMTs and UV applications are explored. The essential qualifications an AlGaN semiconductor material must satisfy to be used as functional device are crack free films, a surface roughness of <1 nm, dislocation densities approaching that of GaN (∼109 cm2) and a reasonable thickness of around 1 μm; each one of the material specifications demand a growth condition that is mostly unfavourable to achieve the other one. To meet these diversified requirements thorough optimisation of growth conditions is carried out. As a result, compositions containing up to 30% AlN-fraction have been achieved. This has been accomplished by understanding the role of growth temperature and buffer design on stress, defect and surface evolution in the AlGaN epilayers. Our studies show that higher AlN-fraction containing epilayers are achievable if stress relaxation during its growth is minimised while simultaneously keeping the growth front smooth under the given growth condition. Such a growth condition can be successfully exploited if the dislocation density at the beginning of epilayer growth is lowered. A smooth heterointerface between Al0.13Ga0.87N and Al0.37Ga0.63N has been realized and formation of 2DEG at this this interface has been confirmed through C-V measurements.

Managing transparency through polymer/perovskite blending: A route toward thermostable and highly efficient, semi-transparent solar cells

Semi-transparent perovskite-based solar cells feature competitive levels of transparency and efficiency, envisioning their future application in building integrated photovoltaics. However, complex processing conditions and thermal stability, inherent of hybrid halide perovskite materials, remain urgent issues to be solved. Herein, the interaction with perovskite precursors and transparency in the visible range of cellulose polymer are explored for the realization of semi-transparent perovskite-polymer composite. Hydroxyethyl cellulose inclusion in CH 3 NH 3 PbI 3 was found to have several beneficial effects, namely, to simplify processing conditions, to improve the average visible transmittance of ~44% and, foremost, to enhance the thermal stability without compromising photovoltaic performances of semi-transparent perovskite solar cells. A maximum light utilization efficiency (LUE) of 2.4% corresponding to a power conversion efficiency of 11.6% was demonstrated, which is in the range usually required for window applications, positioning these semi-transparent solar cells among the most efficient ones reported to date. • Exploiting transparency in the visible range of cellulose polymer to realize semi-transparent perovskite-polymer solar cells. • Simplified perovskite single- step coating and tuning of the transmittance of the device active layer. • Enhanced transmittance of ~ 44% with respect to pristine perovskite yet retaining excellent photovoltaic properties. • Massively improved perovskite materials and solar cells tolerance to thermal stress.

All‐Organic Flexible Ferroelectret Nanogenerator with Fabric‐Based Electrodes for Self‐Powered Body Area Networks

Due to their electrically polarized air-filled internal pores, optimized ferroelectrets exhibit a remarkable piezoelectric response, making them suitable for energy harvesting. Expanded polytetrafluoroethylene (ePTFE) ferroelectret films are laminated with two fluorinated-ethylene-propylene (FEP) copolymer films and internally polarized by corona discharge. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-coated spandex fabric is employed for the electrodes to assemble an all-organic ferroelectret nanogenerator (FENG). The outer electret-plus-electrode double layers form active device layers with deformable electric dipoles that strongly contribute to the overall piezoelectric response in the proposed concept of wearable nanogenerators. Thus, the FENG with spandex electrodes generates a short-circuit current which is twice as high as that with aluminum electrodes. The stacking sequence spandex/FEP/ePTFE/FEP/ePTFE/FEP/spandex with an average pore size of 3µm in the ePTFE films yields the best overall performance, which is also demonstrated by the displacement-versus-electric-field loop results. The all-organic FENGs are stable up to 90°C and still perform well 9 months after being polarized. An optimized FENG makes three light emitting diodes (LEDs) blink twice with the energy generated during a single footstep. The new all-organic FENG can thus continuously power wearable electronic devices and is easily integrated, for example, with clothing, other textiles, or shoe insoles.

Aerosol Assisted Solvent Treatment: A Universal Method for Performance and Stability Enhancements in Perovskite Solar Cells

AbstractMetal‐halide perovskite solar cells (PSCs) have had a transformative impact on the renewable energy landscape since they were first demonstrated just over a decade ago. Outstanding improvements in performance have been demonstrated through structural, compositional, and morphological control of devices, with commercialization now being a reality. Here the authors present an aerosol assisted solvent treatment as a universal method to obtain performance and stability enhancements in PSCs, demonstrating their methodology as a convenient, scalable, and reproducible post‐deposition treatment for PSCs. Their results identify improvements in crystallinity and grain size, accompanied by a narrowing in grain size distribution as the underlying physical changes that drive reductions of electronic and ionic defects. These changes lead to prolonged charge‐carrier lifetimes and ultimately increased device efficiencies. The versatility of the process is demonstrated for PSCs with thick (&gt;1 µm) active layers, large‐areas (&gt;1 cm2) and a variety of device architectures and active layer compositions. This simple post‐deposition process is widely transferable across the field of perovskites, thereby improving the future design principles of these materials to develop large‐area, stable, and efficient PSCs.

Benzodithiophene-Based Spacers for Layered and Quasi-Layered Lead Halide Perovskite Solar Cells.

Incorporating extended pi‐conjugated organic cations in layered lead halide perovskites is a recent trend promising to merge the fields of organic semiconductors and lead halide perovskites. Herein, we integrate benzodithiophene (BDT) into Ruddlesden–Popper (RP) layered and quasi‐layered lead iodide thin films (with methylammonium, MA) of the form (BDT)2MAn−1PbnI3n+1. The importance of tuning the ligand chemical structure is shown as an alkyl chain length of at least six carbon atoms is required to form a photoactive RP (n=1) phase. With N=20 or 100, as prepared in the precursor solution following the formula (BDT)2MAN−1PbNI3N+1, the performance and stability of devices surpassed those with phenylethylammonium (PEA). For N=100, the BDT cation gave a power conversion efficiency of up to 14.7 % vs. 13.7 % with PEA. Transient photocurrent, UV photoelectron spectroscopy, and Fourier transform infrared spectroscopy point to improved charge transport in the device active layer and additional electronic states close to the valence band, suggesting the formation of a Lewis adduct between the BDT and surface iodide vacancies.

Shock-proof and supple multiplex sensor based on Silicon composite fabricated through an energy-free technology

Smart multi-purpose electronic devices are the utmost demanding products for sports, medical, and personal supervision. In smart appliances, silicon (Si) is one of the most common and widely utilized materials with remarkable properties in electronics. Still, the challenge is to exploit it for intelligent and innovative multi-functional applications under changing climate conditions. In this work, we proposed an all-in-one shock-proof and vibration-free smart, flexible multiplex, i.e., optical, thermal, compression, and stress sensor fabricated through energy-free rubbing-in technology. The p-type Si composite with carbon nanotubes (CNTs) and rubber acts as the device's active layer. The CNTs help to boost the conductivity of Si and rubber aid to enhance the flexibility as well as made the device shock and vibration-proof. Eventually, such multi-purpose devices are extremely encouraging for future smart wearable gadgets of the next generation not only due to their small size but also due to their cost-effectiveness.

Multi-Selenophene-Containing Narrow Bandgap Polymer Acceptors for All-Polymer Solar Cells with over 15 % Efficiency and High Reproducibility.

All-polymer solar cells (all-PSCs) progressed tremendously due to recent advances in polymerized small molecule acceptors (PSMAs), and their power conversion efficiencies (PCEs) have exceeded 15 %. However, the practical applications of all-PSCs are still restricted by a lack of PSMAs with a broad absorption, high electron mobility, low energy loss, and good batch-to-batch reproducibility. A multi-selenophene-containing PSMA, PFY-3Se, was developed based on a selenophene-fused SMA framework and a selenophene π-spacer. Compared to its thiophene analogue PFY-0Se, PFY-3Se shows a ≈30 nm red-shifted absorption, increased electron mobility, and improved intermolecular interaction. In all-PSCs, PFY-3Se achieved an impressive PCE of 15.1 % with both high short-circuit current density of 23.6 mA cm-2 and high fill factor of 0.737, and a low energy loss, which are among the best values in all-PSCs reported to date and much better than PFY-0Se (PCE=13.0 %). Notably, PFY-3Se maintains similarly good batch-to-batch properties for realizing reproducible device performance, which is the first reported and also very rare for the PSMAs. Moreover, the PFY-3Se-based all-PSCs show low dependence of PCE on device area (0.045-1.0 cm2 ) and active layer thickness (110-250 nm), indicating the great potential toward practical applications.

Multi‐Selenophene‐Containing Narrow Bandgap Polymer Acceptors for All‐Polymer Solar Cells with over 15 % Efficiency and High Reproducibility

AbstractAll‐polymer solar cells (all‐PSCs) progressed tremendously due to recent advances in polymerized small molecule acceptors (PSMAs), and their power conversion efficiencies (PCEs) have exceeded 15 %. However, the practical applications of all‐PSCs are still restricted by a lack of PSMAs with a broad absorption, high electron mobility, low energy loss, and good batch‐to‐batch reproducibility. A multi‐selenophene‐containing PSMA, PFY‐3Se, was developed based on a selenophene‐fused SMA framework and a selenophene π‐spacer. Compared to its thiophene analogue PFY‐0Se, PFY‐3Se shows a ≈30 nm red‐shifted absorption, increased electron mobility, and improved intermolecular interaction. In all‐PSCs, PFY‐3Se achieved an impressive PCE of 15.1 % with both high short‐circuit current density of 23.6 mA cm−2 and high fill factor of 0.737, and a low energy loss, which are among the best values in all‐PSCs reported to date and much better than PFY‐0Se (PCE=13.0 %). Notably, PFY‐3Se maintains similarly good batch‐to‐batch properties for realizing reproducible device performance, which is the first reported and also very rare for the PSMAs. Moreover, the PFY‐3Se‐based all‐PSCs show low dependence of PCE on device area (0.045–1.0 cm2) and active layer thickness (110–250 nm), indicating the great potential toward practical applications.

Rational Molecular Design of Nonfullerene Acceptors for Bulk Heterojunction Solar Cells

Organic photovoltaics (OPVs) have received considerable attention as clean energy conversion devices because of their lightweightness, cost effectiveness, flexibility, and suitability for roll-to-roll printing. In the past few decades, the active layer of OPV devices has usually consisted of conjugated polymers as donors and fullerene derivatives as acceptors, which typically form a bulk heterojunction (BHJ) structure.1,2 The power conversion efficiency (PCE) of OPVs based on fullerene derivative acceptors has reached over 10%. However, it is difficult to further increase the PCE of fullerene-based OPVs due to their inherent limitations including arduous energy-level tunability and low absorption profile. To enhance the photovoltaic performance of OPVs, nonfullerene acceptors (NFAs) with aromatic fused-ring structures have been extensively developed in recent years to fabricate high-efficiency OPVs. Compared to traditional fullerene acceptors, NFAs possess several advantages, such as facile synthesis and high absorption profile. Most high-performance NFAs possess acceptor-donor-acceptor (A-D-A) type structures, in which fused multi-ring ladder structures are used as the D unit and 1,1-dicyanomethylene-3-indanone (IC) derivatives as the A unit.In this talk I will give an overview of our recent studies on novel nonfullerene acceptors. In paticular, several nonfullerene acceptors possessing different D units have been designed and synthesized to address the relationship between the structure and the photophysical and photovoltaic properties of the A-D-A type nonfullerene acceptors.3,4 [1] T. Umeyama and H. Imahori, J. Mater. Chem. A (Feature Article), 2, 11545-11560 (2014).[2] T. Umeyama and H. Imahori, Acc. Chem. Res. 52, 2046-2055 (2019).[3] T. Umeyama, K. Igarashi, D. Sasada, Y. Tamai, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Ohkita, and H. Imahori, Chem. Sci., 11, 3250-3257 (2020).[4] T. Umeyama, K. Igarashi, D. Sasada, K. Ishida,T. Koganezawa, S. Ohtani, K. Tanaka, and H. Imahori, ACS Appl. Mater. Interfaces, 12, 39236-39244 (2020).

Correlation between Molecular Stereostructure, Film Microstructure, and Electronic Structure of Polyfluorene and Fluorene Based Alternating Copolymers F8BT and PFO–DBT

Identifying key parameters that can help control molecular ordering in the active layer of high-performance organic devices is an important topical issue. Finding a correlation between the spatial ...

Ultra-Lightweight, Flexible InGaP/GaAs Tandem Solar Cells with a Dual-Function Encapsulation Layer.

Lightweight, flexible solar cells from III-V semiconductors offer new application opportunities for devices that require a power supply, such as cars, drones, satellites, or wearable devices, due to their outstanding efficiency and power-to-weight ratio (specific power). However, the specific power and stability of flexible photovoltaic (PV) devices need to be enhanced for use in such applications because current flexible PV devices are vulnerable to moisture and heat. Here, we develop ultra-lightweight, flexible InGaP/GaAs tandem solar cells with a dual-function encapsulation layer that serves as both a moisture barrier and an antireflection coating for the active device layer. Using a thin polymer film as a substrate and an ultrathin metal as a bonding layer, the total weight of the device is dramatically reduced. Therefore, the specific power of our solar cells is remarkably high with a value of over 5000 W/kg under the AM 1.5G solar spectrum. Additionally, there is no degradation even if the solar cells are exposed to harsh environmental conditions.

An organic field effect transistor memory adopting octadecyltrichlorosilane self-assembled monolayer

An organic nonvolatile memory is proposed based on octadecyltrichlorosilane self-assembled monolayer (ODTS SAM) and copper hexadecafluorophthalocyanine (F16CuPc) heterostructure, where F16CuPc acts as the active layer of the organic thin film transistor memory device, and ODTS SAM functions as the charge trapping layer. By adopting N-type active layer, sufficient electrons ensure the erasing process that is independent of the light illumination, indicating a fully electrically driving memory device, where large memory window is obtained. AFM images demonstrates that the monolayer provides the trapping sites. The trapping mechanism is analyzed based on the electric dipoles theory, the dipoles orientation in the monolayer is critical for providing trapping sites, which fixes the mobile carriers at the ODTS SAM/F16CuPc interface. The writing–reading–erasing–reading (WRER) tests and the retention time are shown, and they can be further optimized by involving a thin polystyrene tunneling layer between active layer and charge trapping layer, with an retention time of approximately 125 d, and a sufficient WRER reading current ratio of more than 103 for practical fully electrically driving binary nonvolatile memory device applications.

Eco-Friendly AgBiS2 Nanocrystal / ZnO Nanowire Heterojunction Solar Cells with Enhanced Carrier Collection

Solution-process compatibility and size-dependent bandgap tunability of colloidal quantum dots (CQDs) make them low-cost promising materials for next generation solar cells. Among CQD-based solar cells, heterojunction devices formed with PbS CQDs and ZnO exhibit impressive solar cell performance. However, the hazardous impact of Pb is causing concern. In addition, researches on CQD-based solar cells fabricated using non-toxic and abundant elements are still very limited. Therefore, eco-friendly CQDs for solar cell have drawn much attention. AgBiS2 colloidal nanocrystals with a wide absorption band (0.4-1.2 μm) are one of the alternatives to PbS CQDs. However, the power conversion efficiencies of planar-type heterojunction solar cells using AgBiS2 nanocrystals (NCs) (ITO / ZnO dense layer / AgBiS2 NC layer/ hole transport layers (eg. PTB7:MoOx) / Ag) have been at most approximately 6% mainly due to the short carrier diffusion length of AgBiS2 [2].In this work, thus, we paid our attention to nanowire (NW) structures, with the aim of elongation of carrier diffusion length, and also applied widely-used and less-expensive hole transport materials. We then fabricated NW-type solar cells (ITO / ZnO NW: AgBiS2 mixture / AgBiS2 overlayer / P3HT / Au) by a dip-coating method.We independently tailored ZnO nanowire length and the active device layer thickness to study charge collection in AgBiS2 NW-type solar cell. ZnO NWs were synthesized by a hydrothermal method, and the length of ZnO NW was controlled by the reaction time [3]. As a reference, planar-type solar cells using dense ZnO layers with different thicknesses (NPSC) were also constructed. Jsc values of NPSCs increase as AgBiS2 layer thickness becomes thicker and reach to a maximum value of 12 mA/cm2 at 100 nm. And Jsc then decreases with thickening AgBiS2 layers due to the limited carrier diffusion length of AgBiS2 layer. Whereas in the case of Jsc of NWSCs, the highest Jsc of 20.51 mA / cm2 can be obtained at 200 nm-ZnO NWs. This Jsc value is higher than previously-reported AgBiS2 solar cells (eg. JSC = 15.10 mA/cm2, VOC = 0.46 V, FF = 57%, and PCE = 3.99% [1]), and correspoinding PCE reached 3.97%, approximately doubled the value of planar cell (PCE = 2.06%).Figure 1 shows the EQE spectra obtained with the best performing NWSC and NPSC. It can be seen that NWSC gives high EQE in almost all the spectral region studied. The ZnO NW / AgBiS2 heterojunction enabled achievement of more efficient charge carrier transportation than a planar ZnO NP / AgBiS2 cell. The cell gives a maximum EQE of 80% and shows a wide photocurrent response range of 300-1200 nm. In particular, the EQE is greatly enhanced in the near-infrared region from 35.6% (800 nm) in NPSC to 60.0% in NWSC, indicating improved carrier collection in near-infrared region for NWSC. NWSC also shows higher power conversion efficiency than NPSC because of the higher Jsc of NWSC (inset table in Fig. 1). The length of ZnO NW dependence of NWSC performance was also studied to get a better understanding of diffusion mechanism in NWSC. The structure of NWSCs was optimized by varying nanowire length and active overlayer thickness, carrier transport mechanisms related to the AgBiS2 ZnO-NW blend region and planar AgBiS2 overlayer region were clarified. The solar cell with the 320 nm-thick active layer (200 nm-NW region plus 120 nm-overlayer region) gave the best performance.These results show that ZnO nanowire / AgBiS2 nanocrystal mixtures are useful to achieve more efficient carrier collection. Long-term stability is equally important; at least 3-month air stabilty has been confirmed in NWSCs.[1] M. Bernechea, N. C. Miller, G. Xercavins, et al. Nature Photonics 2016, 10, 521.[2] H. Wang, T. Kubo, J. Nakazaki, T. Kinoshita, H. Segawa. J. Phys. Chem. Lett. 2013, 4, 2455.[3] H. Wang, V. Gonzalez-Pedro, Kubo, T.; F. Fabregat-Santiago, J. Bisquert, Y. Sanehira, J. Nakazaki, H. Segawa. The Journal of Physical Chemistry C 2015, 49, 27265. Figure 1

Reduction of Dark Current in CMOS Image Sensor Pixels Using Hydrocarbon-Molecular-Ion-Implanted Double Epitaxial Si Wafers.

The impact of hydrocarbon-molecular (C3H6)-ion implantation in an epitaxial layer, which has low oxygen concentration, on the dark characteristics of complementary metal-oxide-semiconductor (CMOS) image sensor pixels was investigated by dark current spectroscopy. It was demonstrated that white spot defects of CMOS image sensor pixels when using a double epitaxial silicon wafer with C3H6-ion implanted in the first epitaxial layer were 40% lower than that when using an epitaxial silicon wafer with C3H6-ion implanted in the Czochralski-grown silicon substrate. This considerable reduction in white spot defects on the C3H6-ion-implanted double epitaxial silicon wafer may be due to the high gettering capability for metallic contamination during the device fabrication process and the suppression effects of oxygen diffusion into the device active layer. In addition, the defects with low internal oxygen concentration were observed in the C3H6-ion-implanted region of the double epitaxial silicon wafer after the device fabrication process. We found that the formation of defects with low internal oxygen concentration is a phenomenon specific to the C3H6-ion-implanted double epitaxial wafer. This finding suggests that the oxygen concentration in the defects being low is a factor in the high gettering capability for metallic impurities, and those defects are considered to directly contribute to the reduction in white spot defects in CMOS image sensor pixels.