Optoelectric Characteristics Research Articles

Defect Engineering of MoTe2 via Thiol Treatment for Type III van der Waals Heterojunction Phototransistor.

Molybdenum ditelluride (MoTe2) nanosheets have displayed intriguing physicochemical properties and opto-electric characteristics as a result of their tunable and small band gap (Eg ∼ 1 eV), facilitating concurrent electron and hole transport. Despite the numerous efforts devoted to the development of p-type MoTe2 field-effect transistors (FETs), the presence of tellurium (Te) point vacancies has caused serious reliability issues. Here, we overcome this major limitation by treating the MoTe2 surface with thiolated molecules to heal Te vacancies. Comprehensive materials and electrical characterizations provided unambiguous evidence for the efficient chemisorption of butanethiol. Our thiol-treated MoTe2 FET exhibited a 10-fold increase in hole current and a positive threshold voltage shift of 25 V, indicative of efficient hole carrier doping. We demonstrated that our powerful molecular engineering strategy can be extended to the controlled formation of van der Waals heterostructures by developing an n-SnS2/thiol-MoTe2 junction FET (thiol-JFET). Notably, the thiol-JFET exhibited a significant negative photoresponse with a responsivity of 50 A W-1 and a fast response time of 80 ms based on band-to-band tunneling. More interestingly, the thiol-JFET displayed a gate tunable trimodal photodetection comprising two photoactive modes (positive and negative photoresponse) and one photoinactive mode. These findings underscore the potential of molecular engineering approaches in enhancing the performance and functionality of MoTe2-based nanodevices as key components in advanced 2D-based optoelectronics.

Ultrahigh Responsivity In2O3 UVA Photodetector through Modulation of Trimethylindium Flow Rate

Oxygen vacancies (Vo) can significantly degrade the electrical properties of indium oxide (In2O3) thin films, thus limiting their application in the field of ultraviolet detection. In this work, the Vo is effectively suppressed by adjusting the Trimethylindium (TMIn) flow rate (fTMIn). In addition, with the reduction of the fTMIn, the background carrier concentration and the roughness of the film decrease gradually. And a smooth In2O3 thin film with roughness of 0.44 nm is obtained when the fTMIn is 5 sccm. The MSM photodetectors (PDs) are constructed based on In2O3 thin films with different fTMIn to investigate the opto-electric characteristics of the films. The dark current of the PDs is significantly reduced by five orders from 100 mA to 0.28 μA with the reduction of the fTMIn from 50 sccm to 5 sccm. In addition, the photo response capacity of PDs is dramatically enhanced. The photo-to-dark current ratio (PDCR) increases from 0 to 2589. Finally, the PD with the fTMIn of 5 sccm possesses a record-high responsivity of 2.53 × 103 AW−1, a high detectivity of 5.43 × 107 Jones and a high EQE of 9383 × 100%. Our work provides an important reference for the fabrication of high-sensitivity UV PDs.

Optoelectric characteristics of PVC/SrxZnO nanocomposite films

Poly(Vinyl)Chloride (PVC) films modified by SrxZnO nanoparticles (NPs) were prepared by a simple casting method utilizing its solution in tetrahydrofuran (THF). The PVC films contained 5 wt% of SrxZnO NPs. SrxZnO particles with 0.00, 0.025, 0.05, 0.075 and 0.1 Sr-doping levels were synthesized by the sol-gel method associated with a hydrothermal process. The PVC/SrxZnO films were characterized by XRD, FTIR, Raman, SEM, UV–Visible and PL spectroscopy. XRD analysis demonstrated that SrxZnO into PVC matric are well crystallized in the hexagonal ZnO structure with wurtzite phase, while PVC is in an amorphous state. The particle sizes of SrxZnO vary in the range of 17–31 nm in agreement with the Sr levels. The ATR and Raman spectroscopy verified the existence of a Zn–O bond related to the wurtzite phase. The SEM cross-section views of the films revealed the bulk nature as well as the thicknesses. Strong emission at 733 nm is observed from the PL analysis, associated with Sr content in the PVC/SrxZnO films. Reflectivity, transmittance, and absorption coefficient confirmed the contribution of the physics developed by SrxZnO NPs into the PVC matrix. Urback energies are Sr-level dependent, as a consequence of defects tailoring. Optical transitions (directly and indirectly allowed) decrease in some cases by close to 1 eV indicating a transition of PVC to a semi-crystalline material. Other optical properties including linear and nonlinear characteristics promoted PVC/SrxZnO as a serious candidate for antireflective coating, and a new generation of photovoltaic cells.

Original concept of cracked template with controlled peeling of the cells perimeter for high performance transparent EMI shielding films

The problem of sputtering of thick metal films on micro and nanotemplates is important for obtaining mesh transparent conductors with excellent optoelectric characteristics. In this work, we demonstrate for the first time the possibility of controlling the degree of peeling of the cell perimeter from the substrate for a cracked template based on egg white by alternating the operations of moistening the template with saturated water vapor and shock drying with hot air. Local peeling of the cracked template cells perimeter makes it possible to increase the thickness of the metal sputtered on the cracked template by more than 1 µm, which is not achievable for other lithographic approaches. Our technique was used to obtain thick Ag meshes with a low sheet resistance of no more than 1.59 Ω/sq and a transparency of about 89.1%. The thick Ag meshes show a shielding efficiency (SE) of 49 dB or 99.998% of the incident power of an electromagnetic wave at a frequency of 1 GHz. In a sandwich geometry, thick Ag meshes, which simulates a real shielding window, the shielding efficiency (SE) reaches 71 dB with a transparency of more than 80%.

Nanomaterial-Embedded DNA Films on 2D Frames.

Recently, 3D printing has provided opportunities for designing complex structures with ease. These printed structures can serve as molds for complex materials such as DNA and cetyltrimethylammonium chloride (CTMA)-modified DNA that have easily tunable functionalities via the embedding of various nanomaterials such as ions, nanoparticles, fluorophores, and proteins. Herein, we develop a simple and efficient method for constructing DNA flat and curved films containing water-soluble/thermochromatic dyes and di/trivalent ions and CTMA-modified DNA films embedded with organic light-emitting molecules (OLEM) with the aid of 2D/3D frames made by a 3D printer. We study the Raman spectra, current, and resistance of Cu2+-doped and Tb3+-doped DNA films and the photoluminescence of OLEM-embedded CTMA-modified DNA films to better understand the optoelectric characteristics of the samples. Compared to pristine DNA, ion-doped DNA films show noticeable variation of Raman peak intensities, which might be due to the interaction between the ion and phosphate backbone of DNA and the intercalation of ions in DNA base pairs. As expected, ion-doped DNA films show an increase of current with an increase in bias voltage. Because of the presence of metallic ions, DNA films with embedded ions showed relatively larger current than pristine DNA. The photoluminescent emission peaks of CTMA-modified DNA films with OLEMRed, OLEMGreen, and OLEMBlue were obtained at the wavelengths of 610, 515, and 469 nm, respectively. Finally, CIE color coordinates produced from CTMA-modified DNA films with different OLEM color types were plotted in color space. It may be feasible to produce multilayered DNA films as well. If so, multilayered DNA films embedded with different color dyes, ions, fluorescent materials, nanoparticles, proteins, and drug molecules could be used to realize multifunctional physical devices such as energy harvesting and chemo-bio sensors in the near future.

Optoelectric and photocatalytic characteristics of DNA thin films embedded with transition metal ion-doped ZnO nanorods

While the importance of ZnO nanorods (NR) and DNA molecules has been comprehensively addressed, the characteristics of composite samples comprised of ZnO NRs and DNA have rarely been discussed. Here, we introduced efficient methods to construct ZnO NR powders doped with Ni+2 and Mn+2 via a thermal plasma process and Ni+2- and Mn+2-doped ZnO NR-embedded DNA thin films (labelled Ni–ZnO-DNA-TF and Mn–ZnO-DNA-TF) via drop-casting. The main focus was on investigating the composites’ physical characteristics with varying concentrations of NRs. Based on X-ray diffraction measurement, we observed the crystalline structure of the synthesised ZnO NRs in terms of a Wurtzite hexagonal structure. X-ray photoelectron spectroscopy (XPS) and ultraviolet (UV)–visible spectroscopy were also performed, with the current–voltage properties investigated. The XPS spectra indicated the presence of Zn, Ni and Mn elements in the NRs, as well as core elements in the DNA, while the absorbance and current of the DNA samples with Ni (Mn)–ZnO NRs exhibited a wide absorption range in the UV region and an enhancement of the conductivity. Finally, photocatalytic measurement of specific organic dyes such as methylene blue (MB) and methyl orange (MO) under UV irradiation was carried out to better understand the photocatalytic effect. A notable difference in the degradation of the MB and MO with the ZnO NRs (acting as the photocatalyst) and DNA (acting as an inhibitor of photocatalytic activity) was determined using the degradation rate, which provided relevant information regarding the dye degradation speed under UV light.

Low Cost Embedded Copper Mesh Based on Cracked Template for Highly Durability Transparent EMI Shielding Films.

Embedded copper mesh coatings with low sheet resistance and high transparency were formed using a low-cost Cu seed mesh obtained with a magnetron sputtering on a cracked template, and subsequent operations electroplating and embedding in a photocurable resin layer. The influence of the mesh size on the optoelectric characteristics and the electromagnetic shielding efficiency in a wide frequency range is considered. In optimizing the coating properties, a shielding efficiency of 49.38 dB at a frequency of 1 GHz, with integral optical transparency in the visible range of 84.3%, was obtained. Embedded Cu meshes have been shown to be highly bending stable and have excellent adhesion strength. The combination of properties and economic costs for the formation of coatings indicates their high prospects for practical use in shielding transparent objects, such as windows and computer monitors.

Optoelectric characteristics of laser remote sensing for measurement of ground vibration

Airborne laser remote sensing is extensively used in geophysical explorations. Laser-remote-sensing studies are often undertaken to predict the availability of mineral resources in a target area. A major issue encountered in such studies concerns the acquisition of the ground-vibration information and analysis of the optoelectric characteristics of the corresponding target vibration. Our paper presents a scheme involving the use of a laser remote sensing system (LRSS) to realize the geophone-detection function and experimentally verify the optoelectric characteristics of the target ground vibration. As observed, the proposed LRSS demonstrates a 19- to 98-V s / cm sensitivity range for the low- to medium-frequency vibrations in the 0- to 600-Hz range. Overall, the LRSS could sense a wide range (0 to 4 kHz) of ground-vibration frequencies. Our research is expected to open avenues for electro-optical sensing technologies to be used in applications such as hidden-structure detection and non-line-of-sight imaging.

Effect of substrate on photo-induced persistent photoconductivity in InAs nanowires

The thermal conduction by the difference in the substrate of InAs nanowires (NWs) was investigated by determining the local temperature using Raman spectroscopy as an optical method. The optoelectric characteristics of the supported and suspended InAs nanowires were also investigated. The change in the current with the laser power produced a characteristic profile depending on the InAs nanowire configuration. The persistent photoconductivity (PPC) effect in the InAs nanowires has not been previously studied in detail despite its importance for the material photoresponse. This report presents a study of the PPC effect and the underlying mechanism. The correlation between the PPC effect and the thermal conduction by the substrate-induced carrier redistribution in the InAs nanowires is highlighted. In addition, a unique PPC effect associated with a specific device structure is studied. Our results can enable novel functionalities for InAs-based optoelectric applications in the future.

Phase, current, absorbance, and photoluminescence of double and triple metal ion-doped synthetic and salmon DNA thin films

We fabricated synthetic double-crossover (DX) DNA lattices and natural salmon DNA (SDNA) thin films, doped with 3 combinations of double divalent metal ions (M2+)-doped groups (Co2+–Ni2+, Cu2+–Co2+, and Cu2+–Ni2+) and single combination of a triple M2+-doped group (Cu2+–Ni2+–Co2+) at various concentrations of M2+ ([M2+]). We evaluated the optimum concentration of M2+ ([M2+]O) (the phase of M2+-doped DX DNA lattices changed from crystalline (up to ([M2+]O) to amorphous (above [M2+]O)) and measured the current, absorbance, and photoluminescent characteristics of multiple M2+-doped SDNA thin films. Phase transitions (visualized in phase diagrams theoretically as well as experimentally) from crystalline to amorphous for double (Co2+–Ni2+, Cu2+–Co2+, and Cu2+–Ni2+) and triple (Cu2+–Ni2+–Co2+) dopings occurred between 0.8 mM and 1.0 mM of Ni2+ at a fixed 0.5 mM of Co2+, between 0.6 mM and 0.8 mM of Co2+ at a fixed 3.0 mM of Cu2+, between 0.6 mM and 0.8 mM of Ni2+ at a fixed 3.0 mM of Cu2+, and between 0.6 mM and 0.8 mM of Co2+ at fixed 2.0 mM of Cu2+ and 0.8 mM of Ni2+, respectively. The overall behavior of the current and photoluminescence showed increments as increasing [M2+] up to [M2+]O, then decrements with further increasing [M2+]. On the other hand, absorbance at 260 nm showed the opposite behavior. Multiple M2+-doped DNA thin films can be used in specific devices and sensors with enhanced optoelectric characteristics and tunable multi-functionalities.

Influence of highly-charged 209Bi33+ irradiation on structure and optoelectric characteristics of GaN epilayer

The microstructure and optoelectric properties of GaN epilayer irradiated by highly-charged 209Bi33+ to different fluences are investigated by means of atomic force microscopy, X-ray photoelectron spectroscopy, Raman scattering spectroscopy and photoluminescence spectroscopy. After Bi33+ irradiation, AFM observation shows the irradiated GaN surface is a swelling and swelling rate nonlinearly increases with increasing ions fluence. XPS analysis reveals the relative content of Ga-N bond reduces and Ga-O, Ga-Ga bonds have been produced as the fluence increases. Raman scattering spectra display the thickness of surface depletion layer increases, free carrier concentration and its mobility decrease generally with an increase in ions fluence. Furthermore, the length of Ga-N bond shortens and lattices experience compressive stress with increasing ions fluence are observed from Raman spectra. Room temperature PL spectra reflect the intensity of yellow luminescence (YL) emission increases and its peak has a blueshift after 1.061×1012 Bi33+/cm2 irradiation. Moreover, as the temperature rises, the thermal quenching of YL occurs and its peak position first exhibits a blueshift and then a redshift. Results may be served as a useful reference for HCI to be used in semiconductor fields.

In Situ Growth of 120 cm2 CH3 NH3 PbBr3 Perovskite Crystal Film on FTO Glass for Narrowband-Photodetectors.

Organometal trihalide perovskites have been attracting intense attention due to their enthralling optoelectric characteristics. Thus far, most applications focus on polycrystalline perovskite, which however, is overshadowed by single crystal perovskite with superior properties such as low trap density, high mobility, and long carrier diffusion length. In spite of the inherent advantages and significant optoelectronic applications in solar cells and photodetectors, the fabrication of large-area laminar perovskite single crystals is challenging. In this report, an ingenious space-limited inverse temperature crystallization method is first demonstrated to the in situ synthesis of 120 cm2 large-area CH3 NH3 PbBr3 crystal film on fluorine-doped tin oxide (FTO) glass. Such CH3 NH3 PbBr3 perovskite crystal film is successfully applied to narrowband photodetectors, which enables a broad linear response range of 10-4 -102 mW cm-2 , 3 dB cutoff frequency (f 3 dB ) of ≈110 kHz, and high narrow response under low bias -1 V.

Microcavity 적용 광자 발광 소자의 광 추출 향상 연구

Recently, microcavity is studied to reduce the optical loss of BLU and OLED. In this paper, we suggest applying microcavity to photo-luminescent lamp with plasma discharge technology to meet the display applications for a BLU for LCD. The structure of photo-luminescent lamp consists of SUS foil and ITO glass with microcavity. The opto-electric characteristics of photo-luminescent lamp with microcavity was evaluated. The brightness of photo-luminescent device was increased over <TEX>$111cd/m^2$</TEX> with the adaptation of patterned microcavity at <TEX>$30{\mu}m$</TEX>. The 3D optical simulation verified the enhanced light outcoupling when microcavity applied to the device.

径向桥电极高功率垂直腔面发射激光器

The novel high-power vertical-cavity surface-emitting lasers(VCSEL) with radial bridge electrode is fabricated in order to improve the thermal characteristics and increase the out power of high power VCSEL.The analysis on the model of the high-power VCSEL shows the radial bridge electrode can reduce the electric and thermal resistance and the Joule heat of VCSEL.The radial brigde electrode and the conventional electrode high power VCSEL both with 200μm aperture are made and tested comparatively. The testing results show that the differential resistance of the VCSEL is 0.43Ωand the out power is 340 mW,1.7 times higher than the conventional device,which can operate at higher up to 80℃,and its thermal resistance is 0.95℃/mW.The temperature and opto-electric characteristics of radial bridge electrode high power VCSEL are much better than those of the conventional electrode high power VCSEL.

高功率径向桥电极垂直腔面发射激光器的研制

We report the fabrication of a novel high-power vertical-cavity surface-emitting laser (VCSEL) with radial bridge electrodes in this letter. The analysis shows that the radial bridge electrodes can reduce the p-type distributed Bragg reflector (p-DBR) electric and thermal resistance, and improve the device beam quality. The high-power radial brigde electrode VCSELs with 200-\mum aperture have been made and tested. The testing results show that the differential resistance of the VCSEL is 0.43 \Omega and the maximal continuous-wave (CW) output power is 340 mW, 1.7 times higher than the conventional electrode device. Its thermal resistance is 0.095 \Degress/mW, and its near-field pattern exhibits a homogeneous distribution. The high-power radial bridge electrode VCSEL has better temperature and opto-electric characteristics.

ビナフチル‐フルオレン共重合高分子による直線偏光電場発光

Polyfluorenes have emerged as the most attractive blue-green emitting polymers due to their high efficiency and good thermal stability. It is well known, however, that strong interchain interactions, e.g. excimer formation, in these polymers can lead to luminescence quenching and color change. To improve the color stability, a copolymer has been prepared by coupling of binaphthyl with dialkyl fluorene. Electroluminescence devices were fabricated using the copolymer as a light-emitting layer, and their opto-electric characteristics were evaluated and compared with a device using the homopolymer. Virtually no difference was found in the photoluminescence spectrum of the copolymer film before and after annealing process, indicating improved thermal stability by introducing binaphthyl into the polymer chain. The linearly polarized electroluminescence was observed from the device using the copolymer even without rubbing the substrate.

Characteristics of Silicon Photodetector Using Epitaxial Wafer with High Resistivity and Long Recombination Lifetime

ABSTRACTFor the high quality Si Photodetector, the high resistivity epitaxial wafer using the low resistivity substrate were studied. The buffer layer was introduced in the interface, and it was very effective on the crystal quality of the epitaxial layer. Recombination lifetime in the epitaxial layer became very uniform and long even in the interface region which was confirmed by measuring the lifetime depth profiles. Then Si PIN Photodiode was fabricated on the above high quality epitaxial wafer and its optoelectric characteristics was evaluated.

Optoelectric Characteristics of a-Si/a-SiC Superlattice-Structure Films and Devices Fabricated by the Photo-CVD Method

a-Si/a-SiC superlattice-structure films fabricated by a photo-CVD method were investigated as a wide-bandgap material and applied to window layers of a-Si solar cells. As for carrier transport properties vertical to the interfaces in the dark, I-V characteristics based on tunneling emission and Frenkel-Poole emission were observed with low and high bias voltage regions, respectively. Under illumination of AM-1, 100 mW/cm2, ohmic emission was observed in the same bias voltage region. As for device characteristics, a p/i/n a-Si solar cell whose p-layer was a superlattice-structure was studied. A remarkable increase in the collection efficiency of the cell was found, and it is explained by a calculation by assuming that the superlattice-structure p-layer is an active photogenerating layer. To confirm this, a superlattice-structure p/n diode was fabricated, and it was found that the peak value of the collection efficiency of the diode was five times greater than that of a conventional p/n diode. A conversion efficiency of 11.2% was obtained for a glass/TCO/p-superlattice-structure/i/n/metal a-Si solar cell with p-type doping gas of B(CH3)3.

Opto-Electric Effects in Ge-GaAs p-n Heterojunctions

In an abrupt Ge-GaAs p-n heterojunction, a plot of conduction band edge vs position shows a discontinuity at the material interface. As a result, a ``notch'' occurs in the band-edge profile which strongly affects the opto-electric characteristics of such a junction. The conversion efficiency is much less than that of a homojunction of similar doping levels. At room temperature the photocurrent is limited by the rate at which electrons can be thermally excited from the notch into the GaAs. At 78°K this contribution to current is negligible. For reverse bias, the photocurrent results from electron tunneling from the notch into the GaAs. In forward bias, the space charge resulting from the presence of the optically excited electrons in the notch changes the potential profile in such a way so as to reduce the forward current, and to cut it off entirely for sufficiently high light intensity. Because of the low conversion efficiency, it is concluded that such a heterojunction collector in an optical transistor is not practical.