Cutoff Wavelength Research Articles

Effect of Manganese Alloying on Infrared Detectors Made of Pb1-xMnxTe/CdTe Multilayer Composite.

The properties of Pb1-xMnxTe/CdTe multilayer composite grown by molecular beam epitaxy on a GaAs substrate were studied. The study included morphological characterization by X-ray diffraction, scanning electron microscopy, secondary ion mass spectroscopy, as well as electron transport and optical spectroscopy measurements. The main focus of the study was on the sensing properties of photoresistors made of Pb1-xMnxTe/CdTe in the infrared spectral region. It was shown that the presence of Mn in the Pb1-xMnxTe conductive layers shifted the cut-off wavelength toward blue and weakened the spectral sensitivity of the photoresistors. The first effect was due to an increase in the energy gap of Pb1-xMnxTe with an increase in Mn concentration, and the second was due to a pronounced deterioration in the crystal quality of the multilayers owing to the presence of Mn atoms, as shown by the morphological analysis.

Design and Analysis of a Miniaturized Broadband Resistive Film Absorber to Reduce Chip System Radiation

This study designed a resistive film absorber (RFA) with > 90% absorptivity in the 16–27 GHz broadband to reduce electromagnetic radiation in on-board chip architectures. The size of the RFA unit is miniature, which is only 0.1λ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> × 0.1λ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> × 0.06λ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> (where λ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> is the lowest operating frequency cutoff wavelength). First, the impedance matching and loss principle of the RFA are analyzed based on the intrinsic parametric method and equivalent circuit theory. This explains the influences of each parameter on absorption performance and verifies that the designed RFA has good polarization insensitivity and angle stability. In addition, the measurements of a prototype RFA were obtained and found to be consistent with simulation results, which proves the feasibility of the RFA. Finally, the RFA was added to a chip architecture to verify its electromagnetic suppression effect with consideration of the influence of temperature on absorption performance. The combined simulation results indicate a significant reduction in the far-field radiation values of the chip architecture, with the maximum electromagnetic radiation suppression effect being 12 dB. These results demonstrate the reliability of the proposed electromagnetic suppression scheme and indicate that the RFA has wide application prospects for radiation suppression in chip systems and electronic packaging.

Fabrication of Aromatic Polyimide Films Derived from Diisocyanate with Fluorinated Dianhydride

The range of available structure combinations to synthesize polyimide (PI) makes it technically possible to have various universal methods of producing PI film. The molecular design, in which monomers used to synthesize PI are carefully selected to meet specific application requirements as it influenced the properties of PI films. This study aimed to outline the approach for film fabrication through the casting of highly organo-soluble polyimide derived from 4,4’-methylene diphenyl diisocyanate (MDI) with 4,4’-(hexafluoroisopropylidene) diphtalic anhydride (6FDA) in different heating treatments. The solution drop amount was tested in order to control the films colour uniformity. A flexible and less crystalline MDI-6FDA film with an average thickness of 93 𝜇m was successfully developed with a tensile strength of up to 57 MPa and an elongation at break of 5%. The resulting MDI-6FDA film also demonstrated good optical transparency (T500 = 69%) with a cut-off wavelength at 371 nm and high thermal resistance (T5 = 574 ℃) with a Tg temperature of up to 238 ℃. The obtained film also shows good chemical resistance in methanol, ethanol, isopropanol, and tetrahydrofuran solvents. These outcomes serve as a guideline for the fabrication of polyimide films specifically derived from diisocyanate and dianhydride, with the potential advantages to be used in optical applications.

High-Performance Planar Self-Driven Visible and Near-Infrared Photodetector Based on Pb-Sn Perovskite Single Crystals.

MAPbI3 single crystals (SCs) are promising candidates for self-driven photodetectors due to their spontaneous polarization properties. However, their absorption cutoff wavelength, which is limited to 850 nm, severely hinders their further application in near-infrared photodetectors. In this work, a series of high-quality (MAPbI3)x(FASnI3)1-x (x = 0.8, 0.5 and 0.2) SCs with low defect density and wide absorption range were obtained by employing 1,4-pentanolactone as the solvent at low temperature. Typically, (MAPbI3)0.2(FASnI3)0.8 SCs grown at 32 °C realize absorption in the UV-vis-NIR range from 200 to 1120 nm, which is superior among the absorption wavelengths reported for Pb-Sn perovskite SCs. Resultantly, by merit of the spontaneously polarized built-in electric field, for (MAPbI3)0.2(FASnI3)0.8 SCs based self-driven photodetectors with planar symmetric electrodes exhibiting significant responsivities at 405-1064 nm, the device achieved a maximum responsiveness and detection of 0.247 A/W and 1.17 × 1012 Jones, respectively.

Coupling the full solar spectrum with a two-step thermo-electrolytic cycle for efficient solar hydrogen production

H2O splitting via redox cycles of metal oxides provides a promising path for solar hydrogen production. For various redox cycles with hybrid driving forces, the introduction of spectral splitting is expected to reduce the exergy degradation at the initial step and realize the cascade utilization of the full solar spectrum. A thermodynamic model coupling the full solar spectrum with a two-step thermo-electrolytic cycle was established in this work, based on which the cycling performance was theoretically examined. Solar spectral splitting at an adjustable cut-off wavelength was employed to allow for a flexible allocation of the solar spectrum to meet the thermal and electrical energy demands of the cycle. Solar-to-H2 efficiency can be significantly improved by the introduction of spectral splitting. It can be as high as 35.4% for the redox cycle performed with CeO2-δ, and the optimal reduction temperature can be lowered from 1323 K to 1123 K. Isothermal cycles have an efficiency advantage over non-isothermal cycles due to the elimination of the energy cost for oxygen carrier heating. However, they are also accompanied with lower H2O conversion rates and higher oxygen carrier demands, for which a compromise may be needed from a practical view. Oxygen carriers with lower oxygen affinity were shown to have a higher efficiency potential than pure ceria (CeO2-δ). However, as the reduction enthalpy drops close to or even lower than the enthalpy of direct H2O splitting, the efficiency decreases fast due to insufficient driving force for the oxidation reaction.

Highly-Miniaturized Nano-Plasmonic Filters Based on Stepped Impedance Resonators with Tunable Cut-Off Wavelengths

Highly-Miniaturized Nano-Plasmonic Filters Based on Stepped Impedance Resonators with Tunable Cut-Off Wavelengths

Computational and experimental investigation on piperazinediium bis (4-aminobenzoate) dihydrate single crystal for NLO applications

Piperazinediium bis (4-aminobenzoate) dihydrate (P4AB) single crystal was grown successfully through slow evaporation. Several characterizations of the P4AB crystal were performed to understand its optical, dielectric, thermal, NLO, and structural properties. The structural information of the P4AB crystal was evaluated using single crystal x-ray diffraction (SXRD); P4AB material is an orthorhombic system with a centrosymmetric space group P21/c. The UV–vis–NIR study showed that the P4AB crystal had a large transmission window and exhibited a near-UV cut-off wavelength of 327 nm. The functional groups and their respective band assignments were revealed using Fourier transform infrared (FTIR) analysis. Thermal stability was ascertained through thermogravimetric and differential thermal analysis (TG-DTA). The ions of the incorporated acid compound significantly improved the dielectric, mechanical, and optical properties; they also improved the activation energy and conductivity of the P4AB crystal. In addition, they improved the energy band gap, optical transmittance, and second and third-order nonlinear optical efficiency. The open aperture z-scan technique was employed to investigate the sample's NLO absorption at 532 nm. Quantum chemical calculations were performed with B3LYP/6–311++G (d,p) level of basis set. The optimized geometry, HOMO-LUMO values, and first-order hyperpolarizability were assessed.

Velocity spectra and scale decomposition of adverse pressure gradient turbulent boundary layers considering history effects

Experiments at relatively large Reynolds number were conducted to better understand the influence of an adverse pressure gradient on the turbulence in two-dimensional boundary layer flows. One focus is on documenting the scale contributions to the Reynolds normal and shear stress profiles under the influence of a positive streamwise pressure gradient. Toward these aims, velocity spectra at friction Reynolds numbers (7100≤Reτ≤8600) are presented, analyzed, and compared to a zero pressure gradient case from the same facility at nominally matching Reynolds number. Distance-from-the-wall scaling is central to numerous theoretical and modeling considerations of the canonical flat plate flow. Consistently, the present spectral measurements reveal clear evidence for its preservation on the inertial sublayer under modest adverse pressure gradients. Increases are seen in the viscous-scaled premultiplied spectra in the outer region as the pressure gradient increases — commensurate with the increases observed in the outer peaks of the streamwise and wall-normal velocity variances, as well as the Reynolds shear stress. Effects of varying Reτ on the streamwise and wall-normal velocity variances and the Reynolds shear stress are studied by comparing the present data at varying Clauser pressure gradient parameter, β, with previous experiments having similarly varying β at significantly lower Reτ (≈1900). This allows to study the effects of changing Reynolds number at matched β. Cases at similar β and Reynolds number, but with varying flow history are also examined, wherein the same β value is arrived either by starting from a smaller or larger initial β. The effects of β>0 on the large and small scale motions are investigated by segregating the signal contributions according to a cut-off wavelength established in previous zero pressure gradient flows. Under a normalization that uses a hybrid velocity scale this analysis reveals similarity between the outer regions of the spectrally-decomposed variances and Reynolds shear stress. These analyses also reveal a more dramatic reduction in the near-wall large scale contribution to the Reynolds shear stress gradient in the β>0 flow when compared to the β=0 flow.

Spectral studies and nonlinear optical properties of an organic crystal: Piperazine-1, 4-diiumbis (4-aminobenzenesulfonate)

FTIR, FT-Raman and NMR are studied to explore the functional groups, the vibration modes and its coupling interactions for the grown single crystal piperazine-1,4-diium bis (4-aminobenzenesulfonate) (PABS). The cut-off wavelength at 303 nm of UV–Visible spectrum exhibits great transmittance over the entire visible spectrum. Photoluminescence spectral study revealed the electron excitation notably in blue emission range. The range of susceptibility and nonlinear refractive index was obtained from second and third harmonic generations of PABS crystals. At various temperatures, the thermal stability of the crystal and the crystal dielectric characteristics had been studied in relation to frequency. The hardness of the crystal was obtained by microhardness measurements.

Tosylate family crystals for optoelectronic applications

Since the discovery of lasers, high-quality nonlinear optical (NLO) single crystals have served as the foundation for the creation of novel, cutting-edge devices that meet societal demands. Modern optoelectronic applications such as telecommunication lasers, optical fibers, photodiodes, solar cells, etc. favor high-performance nonlinear optical single crystals with improved optical nonlinearity. Organic crystals are extensively explored for these applications because of their high NLO coefficient. This paper deals with the problems and advancements of organic nonlinear optical single crystals. Here, we review the growth and characterizations of various tosylate family crystals from the vast realm of organic single crystals and their potential applications in the field of optoelectronic devices. Various properties like linear and nonlinear optical, thermal, mechanical, and laser damage threshold values for these samples have been summarized. The attempts are made for highlighting how these tosylate (p-Toluenesulfonic acid based) family crystals can be realized into efficient optoelectronic devices by summarizing variously reported cut-off wavelengths and their wide transmission ranges.

Elastic Gallium Phosphide Nanowire Optical Waveguides-Versatile Subwavelength Platform for Integrated Photonics.

Emerging technologies for integrated optical circuits demand novel approaches and materials. This includes a search for nanoscale waveguides that should satisfy criteria of high optical density, small cross-section, technological feasibility and structural perfection. All these criteria are met with self-assembled gallium phosphide (GaP) epitaxial nanowires. In this work, the effects of the nanowire geometry on their waveguiding properties are studied both experimentally and numerically. Cut-off wavelength dependence on the nanowire diameter is analyzed to demonstrate the pathways for fabrication of low-loss and subwavelength cross-section waveguides for visible and near-infrared (IR) ranges. Probing the waveguides with a supercontinuum laser unveils the filtering properties of the nanowires due to their resonant action. The nanowires exhibit perfect elasticity allowing fabrication of curved waveguides. It is demonstrated that for the nanowire diameters exceeding the cut-off value, the bending does not sufficiently reduce the field confinement promoting applicability of the approach for the development of nanoscale waveguides with a preassigned geometry. Optical X-coupler made of two GaP nanowires allowing for spectral separation of the signal is fabricated. The results of this work open new ways for the utilization of GaP nanowires as elements of advanced photonic logic circuits and nanoscale interferometers.

Gain and Excess Noise in HgCdTe e-Avalanche Photodiodes at Various Temperatures and Wavelengths

Avalanche photodiodes (APDs) can amplify the weak optical signal as well as enable higher receiver sensitivity due to the internal avalanche gain, but the impact ionization process can also introduce the “excess noise”, which limits the practically achievable signal-to-noise ratio (or sensitivity) and gain-bandwidth product. Hg <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1} -\textit{x}}$</tex-math> </inline-formula> Cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula> Te electron-initialed APDs (e-APD) have been demonstrated to exhibit high performance in terms of gain and excess noise at 77 K. Here, we discuss the gain and excess noise properties of multiple Hg <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1}-\textit{x}}$</tex-math> </inline-formula> Cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula> Te e-APDs with different Cd compositions targeting at short-wavelength infrared (SWIR), mid-wavelength infrared (MWIR), and long-wavelength infrared (LWIR) band operating at various temperatures. It demonstrates that the gain of APDs increases as the temperature decreases and the cutoff wavelength of the devices increases, which is related to the decrease of electron effective mass, optical photon scattering rate, and bandgap of the materials. In addition, the low excess noise of less than 1.6 at high gains is also achieved for the devices over a wide range of temperatures. The large spin-orbit splitting energy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $</tex-math> </inline-formula> so) in comparison to bandgap energy is considered to be responsible for the observed pure electron avalanche and exceptionally low excess noise. This work may provide insight into the low-noise HgCdTe APDs and is beneficial for the future applications of high-temperature operating and high-performance optical receivers.

Performance analysis of a novel solar radiation cascade conversion system for combined heat and power generation based on spectrum splitting and reshaping

In this paper, a novel cascading solar photovoltaic system with concentrating spectrum splitting and reshaping for combined heat and power generation is proposed for the first time to break through the limitations of photovoltaic efficiency. Two spectral splitters divide the solar spectrum into three parts, and each part of the spectrum is used by photovoltaics, thermophotovoltaics, and heat exchange fluids according to the photon grade. In addition, the heat exchange fluid also recovers the waste heat of concentrating photovoltaic and thermophotovoltaic cells. Therefore, the system achieves solar energy cascade utilization and has high electrical and thermal efficiency simultaneously. The effect of the fluid flow rate, solar irradiance, and cutoff wavelength of the spectral splitter on the hybrid system is discussed. The results show that under the conditions of 1000 sunlight and outlet fluid temperature of 60 °C, the solar energy conversion rate and exergy efficiency of the hybrid system are 90.17% and 39.84%, which are 63.97 percentage points and 11.62 percentage points higher than those of the single photovoltaic system, respectively.

Megapixel large-format colloidal quantum-dot infrared imagers with resonant-cavity enhanced photoresponse

Infrared imaging is extensively explored due to its unique properties of high atmospheric transmission and temperature-dependent emission. Unfortunately, the current epitaxial infrared materials suffer from a complicated fabrication process and low production yield, which hinders the further development of infrared imaging for civilian applications. As an alternative to epitaxial semiconductors, the wide spectral tunability and optical versatility of colloidal quantum dots (CQDs) have provided a promising route for infrared detection. Here, we demonstrate an infrared imager that integrates HgTe CQDs with complementary metal-oxide-semiconductor (CMOS) readout integrated circuits. Moreover, the underlying metal contacts and passivation layer of the CMOS chip play a role as an in-pixel resonant-cavity , which enhances the absorption of the CQDs film. The CQDs imager exhibits a detectivity of 2.8 × 1010 Jones, an external quantum efficiency of 14%, and an operable pixel factor of over 99.99% for a cut-off wavelength of around 2 µm at room-temperature. With a large-format (1280 × 1024 pixels2) and a small pixel pitch of 15 µm, the resolution of the imager can reach 40 line pairs per millimeter (lp/mm). The performance of the CQDs imager is demonstrated by infrared imaging.

Rational design and coloration mechanism of soluble intrinsic black polyimide with high comprehensive performance for black flexible copper clad laminates

With the development of flexible printed circuit boards (FPCBs) and photoelectric devices, the demand for black polyimide (BPI) is increasing, but the existing BPIs have some problems, such as poor electrical properties, mechanical performance, masking ability and solubility. To solve these problems, a novel diamine monomer (TPCPOHPDA) containing tetraphenylcyclopentadienone (TPCP) grafted with hydroxyl groups and benzene rings was customized, and then TPCPOHPDA was polymerized with 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to obtain polyimide (TPCPOHPPI). TPCP had a broad UV–visible light absorption range (250–600 nm). Appending benzene rings and auxochrome (hydroxyl groups) on the TPCP skeleton extended the conjugated π-electron system and enhanced the mobility of electrons in the large π bonds, respectively. These structural modifications further extended its light absorption range, and the resulting TPCPOHPPI was dark black with a cutoff wavelength (λcut) of 680 nm and Commission International Eclairage (CIE) lab color parameter L* of 0.7. Simulation calculations indicated that the visible-light absorption that caused the black appearance of TPCPOHPPI was mainly due to the electron transition from HOMO to LUMO occurring within the TPCP-containing diamine moieties, in which the charge mainly transferred from the aryl moieties in positions 2 and 5 to the central cyclopentadienone core. Further investigation showed that TPCPOHPPI had excellent thermal, electrical and mechanical performances and high solubility. The TPCPOHPPI-based two-layer black flexible copper clad laminate (2L-FCCL) possessed good dip soldering resistance and peeling strength. This work provides a new idea for the design and synthesis of soluble intrinsic black polyimide with excellent comprehensive performance.

Synthesis, crystal growth and characterization of piperazinium 5-nitrosalicylate (P5NS) single crystal for nonlinear optical (NLO) applications

A single crystal of Piperazinium 5-nitrosalicylate (P5NS) was grown by using slow evaporation solution technique (SEST). The structural analysis (crystal system & cell parameter) of the grown P5NS crystal was examined by single crystal XRD and it exposed that the P5NS crystal has a crystal triclinic system and space group (P-1). Using powder XRD analysis, miller index and (h k l) planes were identified. The P5NS crystal has a sharp cutoff wavelength around 380 nm and is transparent in UV region. The FTIR analysis was investigated on the P5NS crystal to find out the P5NS functional groups. The thermogravimetric and differential thermal analysis illustrate that the P5NS crystal is thermally stable upto 255 °C. Further increase in the temperature resulted in decomposition of P5NS. The etch pit density of P5NS crystal has been calculated by using the chemical etching analysis. The Photoconductivity study reveals that the grown PMC crystal has positive photoconductive nature. The electrical properties, dielectric constant and dielectric loss were determined. The laser damage threshold (LDT) analysis was investigated by Nd: YAG laser and the wavelength of laser is 1064 nm. Intermolecular interactions of P5NS is executed by the Hirshfeld surface analysis. The NLO susceptibility (χ(3)) was calculated by the Z-scan method using the source of He-Ne laser, whose wavelength is 632.8 nm.

Heterostructure axial GaAsSb ensemble near-infrared p–i–n based axial configured nanowire photodetectors

In this work, we present a systematic design of growth experiments and subsequent characterization of self-catalyzed molecular beam epitaxially grown GaAsSb heterostructure axial p–i–n nanowires (NWs) on p-Si <111> for the ensemble photodetector (PD) application in the near-infrared region. Diverse growth methods have been explored to gain a better insight into mitigating several growth challenges by systematically studying their impact on the NW electrical and optical properties to realize a high-quality p–i–n heterostructure. The successful growth approaches are Te-dopant compensation to suppress the p-type nature of intrinsic GaAsSb segment, growth interruption for strain relaxation at the interface, decreased substrate temperature to enhance supersaturation and minimize the reservoir effect, higher bandgap compositions of the n-segment of the heterostructure relative to the intrinsic region for boosting the absorption, and the high-temperature ultra-high vacuum in situ annealing to reduce the parasitic radial overgrowth. The efficacy of these methods is supported by enhanced photoluminescence (PL) emission, suppressed dark current in the heterostructure p–i–n NWs accompanied by increased rectification ratio, photosensitivity, and a reduced low-frequency noise level. The PD fabricated utilizing the optimized GaAsSb axial p–i–n NWs exhibited the longer wavelength cutoff at ∼1.1 μm with a significantly higher responsivity of ∼120 A W−1 (@−3 V bias) and a detectivity of 1.1 × 1013 Jones operating at room temperature. Frequency and the bias independent capacitance in the pico-Farad (pF) range and substantially lower noise level at the reverse biased condition, show the prospects of p–i–n GaAsSb NWs PD for high-speed optoelectronic applications.

Study of the Crystal Architecture, Optoelectronic Characteristics, and Nonlinear Optical Properties of 4-Amino Antipyrine Schiff Bases.

Two Schiff bases, (E)-4-((2-chlorobenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (4AAPOCB) and (E)-4-((4-chlorobenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (4AAPPCB), have been synthesized and grown as single crystals. Single-crystal X-ray diffraction analysis was employed to determine the crystal structure of the compounds, and the results suggest that the compounds crystallized into an orthorhombic crystal system having P212121 and Pbca space groups, respectively. Further, the crystallinity of the compounds was analyzed by the PXRD technique. The UV-vis-NIR spectra of the compounds demonstrate excellent transmittance in the entire visible region. The lower cutoff wavelengths of the compounds were determined to be 338 and 333 nm, respectively; additionally, optical band gaps of the compounds found were 4.60 and 4.35 eV. FTIR and NMR (1H and 13C) spectral techniques were utilized to analyze the molecular structure of the compounds. The compounds emit photoluminescence with broad emission bands with centers at 401 and 418 nm. The thermal stability and phase transitions were assessed through thermogravimetric methods. The phase transition prior to melting was indicated by the endothermic event at around 190 °C in the DTA curves of both crystals, and the same was observed in the DSC curves. The second harmonic efficiencies of the powdered compounds I and II were found to be 3.52 and 1.13 times better than that of the standard reference KDP. The 4AAPOCB and 4AAPPCB compounds showed isotropic polarizability amplitudes of 46.02 × 10-24 and 46.52 × 10-24 esu, respectively. The calculation of linear polarizability and NLO second-order polarizability (β) along with other optical parameters was performed for optimized geometries. The nonzero amplitudes of the average β values for compounds 4AAPOCB and 4AAPPCB were found to be 14.74 × 10-30 and 8.10 × 10-30 esu, respectively, which show a decent potential of the synthesized molecules for NLO applications. The calculated β amplitudes were further explained based on calculated electronic parameters like molecular electrostatic potentials, frontier molecular orbitals, molecular orbital energies, transition energies, oscillator strengths, and unit spherical representation of NLO polarizability. The current analysis emphasizes the significance of synthesized compounds as prospective candidates for optical and NLO applications through the use of experiments and quantum computations.

Quasi-planar InGaAsSb p-B-n photodiodes for spectroscopic sensing.

An InGaAsSb p-B-n structure has been designed and characterized for zero bias low power detection applications. Devices were grown by molecular beam epitaxy and fabricated into quasi-planar photodiodes with a 2.25 µm cut-off wavelength. Maximum responsivity was measured to be 1.05 A/W at 2.0 µm, achieved at zero bias. D* of 9.4 × 1010 Jones was determined from room temperature spectra of noise power measurements with calculated D* remaining >1 × 1010 Jones up to 380 K. With a view to simple miniaturized detection and measurement of low concentration biomarkers, optical powers down to 40 pW were detected, without temperature stabilization or phase-sensitive detection, indicating the photodiode's potential.

Rational design of high-performance soluble intrinsic black polyimide with full absorption of visible light

With the rapid development of photoelectric devices, the demand for black polyimide (BPI) with excellent masking ability is growing, but existing BPI doped with black substrates has serious insulation and mechanical performance deficiencies. To solve the problem, the intrinsic BPI with excellent comprehensive performance is highly desirable. In this work, tetraphenylcyclopentadienone (TPCP) was chosen as a chromophore, a novel diamine (TPCPtPPDA) containing TPCP grafted with biphenyl groups was synthesized, and TPCPtPPDA was then polymerized with 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to obtain a black polyimide (TPCPtPPPI). The TPCPtPPPI showed full absorption of visible light with cutoff wavelength (λcut) high to 713 nm and Commission International Eclairage (CIE) lab color parameter L* of 0.82. By calculating the frontier molecular orbitals and the nature of electron transitions, the excellent light absorption property was attributed to the electron transition from HOMO to LUMO occurring in the diamine moieties, with the charge transfer mainly from the terphenyl moieties in 2 and 5 positions to the central cyclopentadienone core. Meanwhile, TPCPtPPPI also had excellent thermal, electrical and mechanical performances and solubility by introduction of rigid non-planar propeller-shaped structure. This work provides a promising strategy for constructing high-performance soluble intrinsic BPI and related polymers with full absorption of visible light.