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Fabrication and characterization of sensitive vertical P-i-N germanium photodiodes as infrared detectors
摘要： Germanium on silicon P-i-N photodetectors fabricated using standard CMOS tools are now successfully used as uncooled detectors in the near-infrared (NIR), which extends from 0.75 to 1.4 μm and in the short-wave infrared (SWIR), which extends from 1.4 to 3 μm. They feature a remarkably high responsivity up to 1550 nm and a low dark current when they are operated at reverse biases. The aim is to achieve a very low dark current density and a high responsivity with a small Germanium photodiode pitch. In this paper we discuss the fabrication and the characterization of vertical P-i-N photodiodes with the epitaxy of Germanium on Silicon. The Germanium epilayer is a 1.3 μm thick Ge ?lm with a bottom Ge layer P-type doped with boron at 1019 cm?3 and a top Ge layer N-type doped with phosphorus at 1020 cm?3. Secondary ion mass spectroscopy was used to assess the doping level of the Phosphorus doped N?+?region. The strain in the Germanium epilayer on Silicon substrate was investigated. It was tensile, with a value around +0.15% from x-ray diffraction (XRD), in good agreement with a +0.12% value from Raman spectroscopy. In this paper, we focus on P-i-N photodiodes with a circular shape and a diameter of 10 μm. Electrical characterizations were performed in dark and under NIR-SWIR radiation (1310 nm, 1550 nm), with very low dark current of 0.45 nA and enhanced photocurrent at ?1 V. The external responsivities were measured at 0.275 and 0.133 A W?1 for 1310 nm and 1550 nm, respectively. Finally, internal quantum ef?ciencies of the fabricated vertical P-i-N photodiodes were extracted at 66% and 52% at 1310 nm and 1550 nm, respectively, in good agreement with TCAD simulations. Finally, a measurement of the noise in dark conditions is presented.
关键词： infrared detectors,photodiodes,strain,germanium
更新于2025-09-23 15:19:57
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Improved efficiency and photo-stability of methylamine-free perovskite solar cells via cadmium doping
摘要： Although perovskite solar cells containing methylamine cation can show high power conversion efficiency, stability is a concern. Here, methylamine-free perovskite material CsxFA1–xPbI3 was synthesized by a one-step method. In addition, we incorporated smaller cadmium ions into mixed perovskite lattice to partially replace Pb ions to address the excessive internal strain in perovskite structure. We have found that the introduction of Cd can improve the crystallinity and the charge carrier lifetime of perovskite films. Consequently, a power conversion efficiency as high as 20.59% was achieved. More importantly, the devices retained 94% of their initial efficiency under 1200 h of continuous illumination.
关键词： cadmium doping,methylamine-free,lattice strain,photo-stability
更新于2025-09-23 15:19:57
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Direct printing of performance tunable strain sensor via nanoparticle laser patterning process
摘要： Flexible electronics are attractive because of flexibility and portability. The circuits are printed on flexible substrates, which are delicate and heat-sensitive. Traditional photolithography, which uses high temperatures and corrosive chemicals, easily causes damages in flexible substrates. Here, we develop a low-cost nanoparticle based laser patterning process for fabrication of flexible electronics. Nanoparticles are sintered using a low-power laser as they are selectively deposited. Copper and silver particles were successfully deposited on paper and polyethylene terephthalate substrates. The effects of process parameters on deposition performance were studied to understand the process-structure–property relationship. The thermal effects of the laser on film morphology were observed. The sensitivities of the electrical properties with respect to the porosities at different laser power densities were analysed. With different laser energy levels, the process allows for selective deposition, properties control of printed patterns, and flexible substrate cutting. The fabrications of strain sensor and kirigami electronics were demonstrated.
关键词： strain sensor,electrical properties,hybrid manufacturing,Nanoparticle deposition,flexible electronics,process-structure–property relationship
更新于2025-09-23 15:19:57
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Strain engineering of ferroelectric KNbO <sub/>3</sub> for bulk photovoltaic applications: an insight from density functional theory calculations
摘要： A large ferroelectric (FE) polarization and low bandgap are essential to improving the bulk photovoltaic response which is the generation of photocurrent in the polar non-centrosymmetric materials such as FE perovskite oxides. Among various perovskite oxides, Potassium Niobate (KNbO3, KNO) is a promising FE material for bulk photovoltaic applications as its bandgap and polarization can be tuned effectively by strain, doping, or by applying an electric field. In this work, using the density functional theory calculations, we present an insight into the strain engineering of polarization, band structure, and optical properties of the cubic (C), tetragonal (T), and orthorhombic (O) structures of KNO. The tensile and compressive strain under the triaxial, biaxial, and uniaxial conditions are applied along the direction parallel and perpendicular to the polar axis of KNO structures. We find that the bandgap decreases along with a substantial increment of polarization on the application of tensile strain along the direction parallel to the polar axis. In T (O) phase at +2% strain, the polarization increases by 18 μC cm?2 (14 μC cm?2) in triaxial, 26 μC cm?2 (16 μC cm?2) in biaxial, and 29 μC cm?2 (29 μC cm?2) in uniaxial conditions with a considerable decreasing of bandgap with respect to zero strain condition. Therefore, wisely applying the tensile strain along the direction parallel to the polar axis, the photovoltaic efficiency of KNO can be improved.
关键词： density functional theory,bulk-photovoltaic,band gap,strain,polarization
更新于2025-09-23 15:19:57
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Intrinsic-strain-induced curling of free-standing two-dimensional Janus MoSSe quantum dots
摘要： Motivated by the fascinating properties of both two-dimensional transition metal dichalcogenide quantum dots (TMD QDs) and Janus TMD monolayers, we theoretically explore the equilibrium structures of free-standing Janus MoSSe QDs in which atomic asymmetry of chalcogen is introduced. Two distinct types of spontaneous curling are observed by molecular dynamics simulations, and the curling behavior depends on the size of QD. The bowl-like (tube-like) curling occurs in relatively small (large) MoSSe QDs with di?erent shapes (hexagon and triangle) and edge types (zigzag and armchair). The transition between these two curling types occurs at the sizes of around 10 nm and 13 nm for hexagonal and triangular shapes, respectively. By applying equivalent mis?t strains into two adjacent sublayers, ?nite element analysis reproduces similar curling behavior. This con?rms the relaxation of intrinsic strain in Janus structure acting as the predominant driving force of spontaneous curling. In addition, the curvatures of Janus TMD QDs increase from MoSSe to MoSeTe to MoSTe, indicating the positive correlation between the curling and mis?t.
关键词： Intrinsic strain,Janus transition metal dichalcogenides,Molecular dynamics,Quantum dot,Finite element method
更新于2025-09-23 15:19:57
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Dopant Activation of In Situ Phosphorusa??Doped Silicon Using Multia??Pulse Nanosecond Laser Annealing
摘要： Nanosecond laser annealing was performed on ISPD silicon in single- and multi-pulse modes. the active phosphorus concentration was increased with the laser power density and number of laser pulses and more phosphorus was activated with nanosecond lasers than with millisecond lasers. Moreover, almost all the incorporated phosphorus atoms were activated by the nanosecond laser without major strain loss when ISPD silicon melt
关键词： phosphorus-doped silicon,nanosecond laser annealing,diffusion,dopant activation,strain
更新于2025-09-23 15:19:57
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In situ observation of ?′ phase suppression by lattice strain in all-inorganic perovskite solar cells
摘要： The phase control and ordered crystal growth play a crucial role in the efficiency and stability of all-inorganic perovskite solar cells (PSCs). However, the innate dynamics of crystal growth driving the stable phase and high performance are unknown. Here, we for the first time unraveled that the degree of lattice strain is responsible for the suppression of the δ phase growth by in situ Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) technique. We shadow the internal crystal structural changes in real time and successfully decoupled crystal growth dynamics under different substrate temperatures. The symmetrical crystal lattice and vertical substrate growth were finally achieved. This finding provides insights on the inorganic perovskite crystal growth and has significant benefit for high performing all-inorganic PSCs.
关键词： GIWAXS,CsPbI2Br,Inorganic halide perovskite,Lattice strain
更新于2025-09-23 15:19:57
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Inkjet-Printed Organohalide 2D Layered Perovskites for High-Speed Photodetectors on Flexible Polyimide Substrates
摘要： The synthesis of solution-processed two-dimensional organohalide layered (CH3(CH2)3NH3)2(CH3NH3)n?1PbnI3n+1 (n = 2, 3, and 4) perovskites is presented, where inkjet printing was used to fabricate heterostructure flexible photodetector (PD) devices on polyimide (PI) substrates. Inks for the n = 4 formulation were developed to inkjet-print PD devices that were photoresponsive to broadband incoming radiation in the visible regime, where the peak photoresponsivity R was calculated to be ～0.17 A/W, which is higher compared to prior reports, while the detectivity D was measured to be ～3.7 × 1012 Jones at a low light intensity F ≈ 0.6 mW/cm2. The ON/OFF ratio was also high (～2.3 × 103), while the response time τ on the rising and falling edges was measured to be τ ≈ 24 ms and τ ≈ 65 ms, respectively. Our strain-dependent measurements, conducted here for the first time for inkjet-printed perovskite PDs, revealed that the Ip decreased by only ～27% with bending (radius of curvature of ～0.262 cm?1). This work demonstrates the tremendous potential of the inkjet-printed, composition-tunable, organohalide 2D perovskite heterostructures for high-performance PDs, where the techniques are readily translatable toward flexible solar cell platforms as well.
关键词： organohalide 2D perovskites,flexible photodetector,inkjet printing,photoluminescence spectroscopy,strain dependency
更新于2025-09-23 15:19:57
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Design of ultrathin OLEDs having oxide-based transparent electrodes and encapsulation with sub-mm bending radius
摘要： Highly flexible ultrathin organic light emitting diodes (OLEDs) hold vast potential as light sources particularly for wearable and imperceptible electronics. Most of the work demonstrated to date for highly flexible OLEDs, however, has relied on non-conventional transparent conductors such as conjugated polymers and has had no proper encapsulation or, if any, simple polymer-based encapsulation. We here demonstrate OLEDs that can be bent at a sub-mm radius even with conventional transparent conductive oxides (TCOs) and full encapsulation based on a multilayer gas barrier containing aluminum oxides, both of which are prone to strain-induced fracture. We realize such a small bending radius not only by adopting ultrathin substrates but also by exploiting the beneficial neutral plane shift toward the top of substrates identified in a system consisting of a ultrathin substrate and a multilayer device structure on its top. The proposed OLEDs exhibit stable performance after 1,000 bending iterations even at a bending radius far smaller than 1 mm and show similar reliability to that of glass-based reference devices even after two weeks in the acceleration test chamber.
关键词： Transparent conductive oxides,Ultrathin OLEDs,Multilayer encapsulation,Crack-onset strain,Neutral plane shift
更新于2025-09-23 15:19:57
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GaN/InAlN chirped short period superlattice as strain free top cladding for blue laser diode
摘要： This work presents the theoretical study on strain-free chirped short-period superlattices (C-SPSL) as the top waveguide core and cladding layers for InGaN laser diodes (LDs) emitting at 450 nm. The total 530 nm thick layers of reference LD containing 100 nm p-GaN waveguide, 30 nm Al0.15Ga0.85N electron blocking layer (EBL) and Al0.065Ga0.935N cladding layers are replaced by 300 nm thick C-SPSL which contains the 33-periods of 10 monolayers (ML) GaN/ 2 ML In0.18Al0.82N, 48-periods of 6 ML GaN/2 ML In0.18Al0.82N, and 97-periods of 2 ML GaN/ 2 ML In0.18Al0.82N. The optical confinement factor of reference LD is 3.28% whereas for C-SPSL LD it is 3.42%. The better optical confinement at reduced thickness using C-SPSL is due to the high refractive index contrast. The strain in the C-SPSL is negligible. The electron leakage has reduced from 2.54 kA-cm-2 to 0.166 kA-cm-2 at ~10 kA-cm-2 injected current density, whereas the hole transportation has improved by 2.31 kA-cm-2. The C-SPSL configuration also favours the electron blocking effect, thus EBL is not required in C-SPSL design. The light output power at a current injection of 500 mA (10 kA-cm-2) is 248 mW for the new structure and ~143 mW for reference LD. The slope efficiency is improved from ~0.55 W/A to ~0.89 W/A. Also, the dynamic resistance from I-V characteristic is ~ 1.12 Ω which is lowered to ~0.94 Ω.
关键词： superlattice cladding,strain-free top cladding,Short-period superlattice,InGaN Laser Diode
更新于2025-09-23 15:19:57