Photodetectors based on reduced graphene oxide (rGO) have attracted much attention owing to their simple and low‐cost fabrication process. However, the aggregation and defects of rGO flakes still ...limit the performance of rGO photodetectors. Controlling the composition of rGO has become a vital factor for its prospective applications. For example, the interconnection between rGO and polymers for modified morphologies of rGO films leads to an enhanced performance of devices. In this work, a practical approach to engineer surface uniformity and enhance the performance of a photodetector by modifying the rGO film with hydrophilic polymers poly(vinyl alcohol) (PVA) is reported. Compared with the rGO photodetector, the on/off ratio for the PVA/rGO photodetector shows 3.5 times improvement, and the detectivity shows 53% enhancement even when the photodetector is operated at a low bias of 0.3 V. This study provides an effective route to realize PVA/rGO photodetectors with a low‐power operation which shows promising opportunities for the future development of green systems.
A practical approach to enhance the performance of a reduced graphene oxide (rGO) photodetector by modifying the rGO film with poly(vinyl alcohol) (PVA) is reported. Compared with the rGO photodetector, the on/off ratio for the PVA/rGO photodetector shows 3.5 times improvement, and the detectivity shows 53% enhancement at a low operating bias of 0.3 V.
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All-solution-processed reduced graphene oxide (rGO)-based flexible photodetectors (PDs) with asymmetric electrode structures of Ag nanowires (NWs) - Cu NWs are demonstrated for stable photodetection ...in weak-light environments. At first, we aimed to optimize the fabrication parameters of rGO layers for minimum roughness and high uniformity according to the field emission scanning electron microscope (FESEM) images; the average absorbance of optimal rGO layers is <inline-formula> <tex-math notation="LaTeX">\sim </tex-math></inline-formula>17.4% from 400 to 1600 nm. Additionally, compared to Ag NWs - Ag NWs and Cu NWs - Cu NWs electrodes, rGO PDs with Ag NWs-Cu NWs asymmetric electrodes showed a higher photocurrent-to-dark-current ratio (PDCR) (<inline-formula> <tex-math notation="LaTeX">\sim </tex-math></inline-formula>6), which was due to the improved carrier transport with using Ag and Cu as cathodes and anodes. Furthermore, the highest photoresponsivity (5.5 mA/W) and detectivity (<inline-formula> <tex-math notation="LaTeX">D^{\ast} </tex-math></inline-formula>) (<inline-formula> <tex-math notation="LaTeX">\sim {1}\times {10}^{{9}} </tex-math></inline-formula> cm Hz<inline-formula> <tex-math notation="LaTeX">^{{{1}/{2}}} </tex-math></inline-formula>/W) of rGO PDs with Ag NWs - Cu NWs electrodes have been measured and evaluated at 8 V bias. This work demonstrates the significant potential of all-solution processed rGO-based flexible PDs for high-performance and low-cost photosensing applications.
A cost-effective approach of building graphene-based photodetectors with Ag nanowires (AgNWs) as the contact electrode on the glass substrate via solution process has been developed. The ...transmittance of the graphene/glass and the AgNWs/graphene/glass at a wavelength of 550 nm is 74% and 67%, respectively. To further improve the performance of the graphene photodetector, Ag nanoparticles are applied on the graphene to obtain the enhanced photocurrent and the improved ON/OFF ratio of 505 by the surface plasmon resonance effect. This semi-transparent graphene photodetector shows the superior optical and electrical performance and it paves the way to the future development of graphene-based devices by costly and high-throughput techniques.
This work demonstrates a self-powered and broadband photodetector using a heterojunction formed by camphor-based chemical vaper deposition (CVD) bilayer graphene on p-Si substrates. Here, ...graphene/p-Si heterostructures and graphene layers serve as ultra-shallow junctions for UV absorption and zero bandgap junction materials (<Si bandgap (1.1 eV)) for long-wave near-infrared (LWNIR) absorption, respectively. According to the Raman spectra and large-area (16 × 16 μm2) Raman mapping, a low-defect, >95% coverage bilayer and high-uniformity graphene were successfully obtained by camphor-based CVD processes. Furthermore, the carrier mobility of the camphor-based CVD bilayer graphene at room temperature is 1.8 × 103 cm2/V·s. Due to the incorporation of camphor-based CVD graphene, the graphene/p-Si Schottky junctions show a good rectification property (rectification ratio of ~110 at ± 2 V) and good performance as a self-powered (under zero bias) photodetector from UV to LWNIR. The photocurrent to dark current ratio (PDCR) value is up to 230 at 0 V under white light illumination, and the detectivity (D*) is 8 × 1012 cmHz1/2/W at 560 nm. Furthermore, the photodetector (PD) response/decay time (i.e., rise/fall time) is ~118/120 μs. These results support the camphor-based CVD bilayer graphene/Si Schottky PDs for use in self-powered and ultra-broadband light detection in the future.
A transfer-free graphene with high magnetoresistance (MR) and air stability has been synthesized using nickel-catalyzed atmospheric pressure chemical vapor deposition. The Raman spectrum and Raman ...mapping reveal the monolayer structure of the transfer-free graphene, which has low defect density, high uniformity, and high coverage (>90%). The temperature-dependent (from 5 to 300 K) current-voltage (
) and resistance measurements are performed, showing the semiconductor properties of the transfer-free graphene. Moreover, the MR of the transfer-free graphene has been measured over a wide temperature range (5-300 K) under a magnetic field of 0 to 1 T. As a result of the Lorentz force dominating above 30 K, the transfer-free graphene exhibits positive MR values, reaching ∼8.7% at 300 K under a magnetic field (1 Tesla). On the other hand, MR values are negative below 30 K due to the predominance of the weak localization effect. Furthermore, the temperature-dependent MR values of transfer-free graphene are almost identical with and without a vacuum annealing process, indicating that there are low density of defects and impurities after graphene fabrication processes so as to apply in air-stable sensor applications. This study opens avenues to develop 2D nanomaterial-based sensors for commercial applications in future devices.
The development of n-type Cu2O has become essential for realizing high-efficiency PV devices based on Cu2O homojunctions, thereby avoiding the numerous efficiency-reducing defects common in ...heterojunctions. To the best of our knowledge, we are the first to fabricate chlorine (Cl)-doped cuprous oxide (Cu2O:Cl) thin films on a copper (Cu) substrate by using the chemical bath deposition (CBD) method. The Cu2O:Cl films were prepared using copper sulfate (CuSO4) solution with the addition of copper chloride (CuCl2) as a Cl− source. After the molar ratio of CuCl2 to CuSO4 (CuCl2/CuSO4) was varied from 0 to 2.01, hot-point probe measurements showed n-type conductivity for all the Cu2O films produced by CBD. X-ray diffraction patterns indicate that the as-grown Cu2O:Cl films have a sphalerite structure with a dominant plane orientation of Cu2O(111) parallel to the substrate surface for CuCl2/CuSO4 of less than 1.19, while the CuCl(111) phase became dominant when CuCl2/CuSO4 was greater than 1.19. Moreover, low-temperature photoluminescence (PL) measurements conducted at 5 K demonstrated an emission band at 1.902 eV, related to Cl doping, in addition to the emission band at 1.715 eV, attributed to doubly ionized oxygen vacancies. We found that the Cl-related PL emission was intensified with increasing amounts of Cl involved. The incorporation of Cl into the lattice of Cu2O was also confirmed by X-ray photoelectron spectroscopy. Our findings indicate that n-type Cu2O:Cl films with a resistivity ranging from 40-50 Ω·cm can be produced on Cu substrate by the CBD method.
Graphene has unique and outstanding properties that make it a promising material for many applications. It has triggered considerable research in fields including solar cells, photodetectors, ...electrodes, and supercapacitors. Despite the favorable characteristics of devices using graphene have been widely explored, issues such as low absorbance, complex processing, and limited device size remain. Hence, we present large-area CdSe quantum dots (QDs)/reduced graphene oxide (rGO) films and corresponding photodetectors through a cost-effective and simple spin-coating method. As light turns on, CdSe QDs are excited and generate excess electron-hole pairs, leading to a significantly increased on/off current ratio of 2195 at a low bias voltage of −1 V, compared to that of photodetectors without CdSe QDs. Decorating the rGO film with CdSe QDs enables the wavefunction modulation and enhances the light harvesting. Our proposed high-performance photodetector can be operated at a low voltage, which is beneficial for applications in various green and low-power consumption devices.
The unique and outstanding electrical and optical properties of graphene make it a potential material to be used in the construction of high-performance photosensors. However, the fabrication process ...of a graphene photosensor is usually complicated and the size of the device also is restricted to micrometer scale. In this work, we report large-area photosensors based on reduced graphene oxide (rGO) implemented with Ag nanoparticles (AgNPs) via a simple and cost-effective method. To further optimize the performance of photosensors, the absorbance and distribution of the electrical field intensity of graphene with AgNPs was simulated using the finite-difference time-domain (FDTD) method through use of the surface plasmon resonance effect. Based on the simulated results, we constructed photosensors using rGO with 60⁻80 nm AgNPs and analyzed the characteristics at room temperature under white-light illumination for outdoor environment applications. The on/off ratio of the photosensor with AgNPs was improved from 1.166 to 9.699 at the bias voltage of -1.5 V, which was compared as a sample without AgNPs. The proposed photosensor affords a new strategy to construct cost-effective and large-area graphene films which raises opportunities in the field of next-generation optoelectronic devices operated in an outdoor environment.
The Mg0.1Zn0.9O films were grown using atomic layer deposition (ALD) system and applied to metal-semiconductor-metal ultraviolet photodetectors (MSM-UPDs) as an active layer. To suppress the dangling ...bonds on the Mg0.1Zn0.9O surface, the photoelectrochemical (PEC) treatment was used to passivate the Mg0.1Zn0.9O surface, which could reduce the dark current of the MSM-UPDs about one order. Beside, to increase more incident light into the Mg0.1Zn0.9O active layer of the MSM-UPDs, the 500-nm-diameter silica nanospheres were spin-coated on the Mg0.1Zn0.9O active layer to improve the antireflection capability at the wavelength of 340 nm. The reflectivity of the Mg0.1Zn0.9O films with silica nanospheres antireflection layer decreased about 7.0% in comparison with the Mg0.1Zn0.9O films without silica nanospheres. The photocurrent and UV-visible ratio of the passivated Mg0.1Zn0.9O MSM-UPDs with antireflection layer were enhanced to 5.85 μA and 1.44 × 10 4 , respectively, at the bias voltage of 5 V. Moreover, the noise equivalent power and the specific detectivity of the passivated Mg0.1Zn0.9O MSM-UPDs with antireflection layer were decreased to 2.60 × 10 - 13 W and increased to 1.21 × 10 12 cmHz1/2W−1, respectively, at the bias voltage of 5 V. According to the above mentions, the PEC treatment and silica nanospheres antireflection layer could effectively enhance the performance of Mg0.1Zn0.9O MSM-UPDs.
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Ga-doped zinc oxide (ZnO:Ga) films were grown on glass substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) using diethylzinc and water as reactant gases and triethyl ...gallium (TEG) as an n-type dopant gas. The structural, electrical and optical properties of ZnO:Ga films obtained at various flow rates of TEG ranging from 1.5 to 10 sccm were investigated. X-ray diffraction patterns and scanning electron microscopy images indicated that Ga-doping plays an important role in forming microstructures in ZnO films. A smooth surface with a predominant orientation of (101) was obtained for the ZnO:Ga film grown at a flow rate of TEG
=
7.5 sccm. Moreover, a lowest resistivity of 3.6
×
10
−
4
Ω cm and a highest mobility of 30.4 cm
2 V
−
1
s
−
1
were presented by the same sample, as evaluated by Hall measurement. Otherwise, as the flow rate of TEG was increased, the average transmittance of ZnO:Ga films increased from 75% to more than 85% in the wavelength range of 400–800 nm, simultaneously with a blue-shift in the absorption edge. The results obtained suggest that low-resistivity and high-transparency ZnO films can be obtained by AP-MOCVD using Ga-doping sufficiently to make the films grow degenerate and effect the Burstein–Moss shift to raise the band-gap energy from 3.26 to 3.71 eV.
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