Photoresponse Measurements Research Articles

Acepromazine and Chlorpromazine as Pharmaceutical-grade Alternatives to Chlorprothixene for Pupillary Light Reflex Imaging in Mice.

Studies of visual responses in isoflurane-anesthetized mice often use the sedative chlorprothixene to decrease the amount of isoflurane used because excessive isoflurane could adversely affect light-evoked responses. However, data are not available to justify the use of this nonpharmaceutical-grade chemical. The current study tested whether pharmaceutical-grade sedatives would be appropriate alternatives for imaging pupillary light reflexes. Male 15-wk-old mice were injected intraperitoneally with 1 mg/kg chlorprothixene, 5 mg/kg acepromazine, 10 mg/kg chlorpromazine, or saline. After anesthetic induction, anesthesia maintenance used 0.5% and 1% isoflurane for sedative- and saline-injected mice, respectively. A photostimulus (16.0 log photons cm-2 s-1; 470 nm) was presented to the right eye for 20 min, during which the left eye was imaged for consensual pupillary constriction and involuntary pupil drift. Time to immobilization, loss of righting reflex, physiologic parameters, gain of righting reflex, and degree of recovery were assessed also. The sedative groups were statistically indistinguishable for all measures. By contrast, pupillary drift occurred far more often in saline-treated mice than in the sedative groups. Furthermore, saline-treated mice took longer to reach maximal pupil constriction than all sedative groups and had lower heart rates compared with chlorpromazine- and chlorprothixene-sedated mice. Full recovery (as defined by purposeful movement, response to tactile stimuli, and full alertness) was not regularly achieved in any sedative group. In conclusion, at the doses tested, acepromazine and chlorpromazine are suitable pharmaceutical-grade alternatives to chlorprothixene for pupil imaging and conceivably other in vivo photoresponse measurements; however, given the lack of full recovery, lower dosages should be investigated further for use in survival procedures.

Morphological, structural and photoresponse characterization of ZnO nanostructure films deposited on plasma etched silicon substrates

ZnO nanostructure films were deposited by radio frequency (RF) magnetron sputtering on etched silicon (100) substrates using dry Ar/SF6 plasma, at two etching times of 5 min and 30 min, and on non etched silicon surface. Energy dispersive X-ray (EDX) technique was employed to investigate the elements contents for etched substrates as well as ZnO films, where it is found to be stoichiometric. Surface and growth evolution of films were explored by scanning electron microscope (SEM) images and found to have morphological development from spherical forms into nanowires with increasing substrate etching time. 2D atomic force microscope (AFM) images clarify this modification of the morphology and roughness values are deduced. Structural study was investigated using X-ray diffraction (XRD) patterns. The films had (002) preferential orientation with various etching time substrates. Optical characterization illustrated a decrease of reflectance with the morphological modification. Photoresponse measurement has been investigated and correlated with the crystallinity.

An ultrasensitive self-driven broadband photodetector based on a 2D-WS2/GaAs type-II Zener heterojunction.

High-performance broadband photodetectors have attracted extensive research interest because of their significance in optoelectronic applications. In this study, a highly sensitive room-temperature (RT) broadband photodetector composed of a WS2/GaAs type-II van der Waals heterojunction was demonstrated, which exhibited obvious photoresponse to broadband light illumination from 200 to 1550 nm beyond the limitation of the bandgaps. Impressive device performances were achieved in terms of a low noise current of ∼59.7 pA, a high responsivity up to 527 mA W-1, an ultrahigh Ilight/Idark ratio of 107, a large specific detectivity of 1.03 × 1014 Jones, a minimum detection light intensity of 17 nW cm-2 and an external quantum efficiency (EQE) up to 80%. Transient photoresponse measurements revealed that the present detector is capable of working at a high frequency with a 3 dB cutoff frequency up to 10 kHz and a corresponding rise/fall time of 21.8/49.6 μs. Notably, this heterojunction device demonstrated Zener tunneling behaviors with a threshold voltage of -4 V. The capacitance-voltage (C-V) properties of the heterojunction were investigated to understand the device performances. In addition, the as-fabricated device can function as an image sensor with an outstanding imaging capability. Considering the above superior features, the proposed WS2/GaAs type-II van der Waals heterojunction may find great potential in high-performance broadband photodetection applications.

Effect of thickness on the performance of solar blind photodetectors fabricated using PLD grown β-Ga2O3 thin films

Herein, we are reporting the fabrication of high-performance solar blind photodetectors using β-Ga2O3 thin films of varying thicknesses grown on single crystal (0001) Sapphire substrate by pulsed laser deposition (PLD) technique. Thickness of the β-Ga2O3 films was varied by varying the number of ablating laser shots from 1000 to 15,000 (1 k to 15 k). The effect of thickness on the structure, surface morphology and optical properties of the films was investigated using several state-of-the-art techniques such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectroscopy. All the films were found to be made of phase-pure β-Ga2O3 with high crystal quality. The orientation of the films was found to gradually change from (−201) to (−201)/(400) as the number of laser shots increased from 1 k to 15 k. The bandgap of the films made with 1 k laser shots was found to be 5.26 eV which decreased monotonously with increase in number of laser shots and became 4.79 eV for the films made with 15 k laser shots. The detailed time-resolved photoresponse measurements showed that the films made with 2 k shots exhibit the best photoresponse characteristic among all the films with a high Iphoto/Idark ratio of ∼6.7 × 104 and short rise (0.38 μs) and decay times (142 μs). Our results indicate that the PLD-grown β-Ga2O3 thin films, with optimized thickness, can play a major role in next-generation solar-blind ultraviolet photodetector technology.

Mechanisms behind slow photoresponse character of Pulsed Electron Deposited ZnO thin films

Semiconducting Zinc Oxide (ZnO) is ideal candidate for ultraviolet (UV) photodetector due to its promising optoelectronic properties. Photoconductive type ZnO photodetectors, which is fabricated in metal-semiconductor-metal configuration, show mostly very high photoconductivity under UV light, but they are plagued by slow photoresponse time as slow as several tens of hours, even more. Most of the studies claimed that atmospheric adsorbates such as water and oxygen create charge traps states on the surface and remarkably increase both the photoconductivity and response time. There are also limited studies, which claim that the defect states acting as hole trap centers prolong response time significantly. However, the underlying physical mechanism is still unclear. Here we study the effects of both adsorbates and defect-related states on the photoresponse character of Pulsed Electron Deposited ZnO thin films. In order to distinguish between these two mechanisms, we have compared the time-dependent photoresponse measurements of bare-ZnO and SiO2 encapsulated-ZnO thin film samples taken under UV light and high vacuum. We show that the dominant mechanism of photoresponse in ZnO is the adsorption/desorption of oxygen and water molecules even when the measurement is performed in high vacuum. After the encapsulation of sample surface by a thin SiO2 layer, the adsorption/desorption rates can significantly improve, and the effects of these molecules partially removed.

Synthesis of Hollow Cu2ZnSnSe4 Nanocrystals by Hot-Injection Method

Hollow-shape colloidal Cu2ZnSnSe4 nanocrystals were successfully synthesized in this study using hot-injection method. TEM, XRD, Raman, XPS, UV-Vis-NIR, and photo response measurements were carried out to characterize the hollow nanocrystals. These hollow nanocrystals were found to have tetragonal structure and high crystallinity, and were Zn-rich in composition. The optical band gap for the hollow Cu2ZnSnSe4 nanocrystals was determined to be about 1.12 eV. The hollow Cu2ZnSnSe4 nanocrystals have potential applications in the photoelectric field.

Bolometric Effect in Bi2 O2 Se Photodetectors.

Bi2 O2 Se is emerging as a photosensitive functional material for optoelectronics, and its photodetection mechanism is mostly considered to be a photoconductive regime in previous reports. Here, the bolometric effect is discovered in Bi2 O2 Se photodetectors. The coexistence of photoconductive effect and bolometric effect is generally observed in multiwavelength photoresponse measurements and then confirmed with microscale local heating experiments. The unique photoresponse of Bi2 O2 Se photodetectors may arise from a change of hot electrons during temperature rises instead of photoexcited holes and electrons. Direct proof of the bolometric effect is achieved by real-time temperature tracking of Bi2 O2 Se photodetectors under time evolution after light excitation. Moreover, the Bi2 O2 Se bolometer shows a high temperature coefficient of resistance (-1.6% K-1 ), high bolometric coefficient (-31 nA K-1 ), and high bolometric responsivity (>320 A W-1 ). These findings offer a new approach to develop bolometric photodetectors based on Bi2 O2 Se layered materials.

Bi2Te3 photoconductive detector under weak light

Bi2Te3 − xSex photoconductive detectors are attractive due to their linear photo-response (LPR), potential in ultrabroadband photo-detection, and compatibility with CMOS technology. However, as a fundamental issue for photo-detectors, the weak-light photo-response of Bi2Te3 − xSex detectors was covered by the bolometric response, the photo-thermoelectric effect, and the 300 K background black-body radiation from the optical window. Here, using a window-less system, we systematically measure the weak-light photo-response of a Bi2Te3 photoconductive detector. The bolometric response and photo-thermoelectric effect are carefully excluded. It shows that LPR can persist to a small light power density of P < 10−8 W/cm2. Meanwhile, the response is maximized at ∼80 K temperature. We suggest that the LPR is rooted in the unique carrier recombination configuration of Bi2Te3, which can result in a constant lifetime for light-generated carriers. The concerned trap level is manifested by a negative photo-response under reduced light intensity. The signature of surface state related signal is presented as a photo-response with the maximum at ∼10 K temperature, which is fragile under increased light intensity. Although the window-less photo-response measurement is at its early stage, it provides a perspective which is different from that of the traditional optical-window based measurement.

Patterned Quantum Dot Photosensitive FETs for Medium Frequency Optoelectronics

AbstractThe use of colloidal quantum dots (CQDs) as active layers for the transistors in integrated circuits is often impeded by the poor compatibility of CQDs films with the standard lithographic processing. Successful patterning of tetrabutylammonium iodide‐treated PbS CQDs films is demonstrated on (3‐aminopropyl)triethoxysilane (APTES) functionalized glass or aluminum oxide surfaces, using lithography. Short‐channel (4 µm) field‐effect transistors (FETs) with patterned gate electrode and patterned CQDs film as active layer with electron mobility of 0.1 cm2 V−1 s−1, threshold voltage of −0.29 V, and cutoff frequency of 400 kHz are demonstrated. Furthermore, the lithographic processing does not compromise the optical properties of the film, as evidenced by the photoresponse measurements of the FETs (11.6 mA W−1 at 920 nm and 26.7 mA W−1 at 440 nm). These results further demonstrate CQDs as a potential material for optoelectronic applications, where medium frequency operation is required.

Electrical and optical properties of photodiode structures formed by surface polymerization of P(Egdma-Vpca)-Swcnt films on n-si

Abstracts Poly (ethylene glycol dimethacrylate-1-vinyl-1H-pyrrole-2-carboxylic acid)/carbon nanotube, single-walled)/n-Si ([P(EGDMA-VPCA)-SWCNT]/n-Si) photodiode structures was fabricated by using surface polymerization method. While electrical properties were measured at different temperatures, optical properties were measured at room temperatures. Dark and light current characteristics were investigated. Spectral photoresponse measurements of the structure were realized at room temperature. They showed that the fabricated structure exhibited rectification behavior, which makes it a good nominee for optoelectronic implementation area.

Optical and electrical properties of two-dimensional palladium diselenide

Two-dimensional (2D) noble-metal dichalcogenides exhibit exceptionally strong thickness-dependent bandgaps, which can be leveraged in a wide variety of device applications. A detailed study of their optical (e.g., optical bandgaps) and electrical properties (e.g., mobilities) is important in determining potential future applications of these materials. In this work, we perform detailed optical and electrical characterization of 2D PdSe2 nanoflakes mechanically exfoliated from a single-crystalline source. Layer-dependent bandgap analysis from optical absorption results indicates that this material is an indirect semiconductor with bandgaps of approximately 1.37 and 0.50 eV for the monolayer and bulk, respectively. Spectral photoresponse measurements further confirm these bandgap values. Moreover, temperature-dependent electrical measurements of a 6.8-nm-thick PdSe2 flake-based transistor show effective electron mobilities of 130 and 520 cm2 V−1 s−1 at 300 K and 77 K, respectively. Finally, we demonstrate that PdSe2 can be utilized for short-wave infrared photodetectors. A room-temperature specific detectivity (D*) of 1.8 × 1010 cm Hz1/2 W−1 at 1 μm with a band edge at 1.94 μm is achieved on a 6.8-nm-thick PdSe2 flake-based photodetector.

High performance visible photodetectors based on thin two-dimensional Bi2Te3 nanoplates

Two-dimensional (2D) nanostructures, bismuth telluride (Bi2Te3), as represented by one of the topological insulators (TI) materials, have attracted tremendous interests from world-wide scientists due to their potential applications in electronic devices. However, the growth mechanism especially chemical vapour deposition (CVD) and the optoelectronic device applications of these Bi2Te3 nanostructures have barely been investigated and reported. In this work, we present a detailed study on the controlled CVD growth of 2D Bi2Te3 nanostructures and explore their applications in high performance visible photodetectors. With increasing the precursor material temperature from 470 °C to 510 °C, it is observed that the lateral size of Bi2Te3 nanoplates first increases and then becomes saturated when the precursor material temperature over 490 °C, which is mainly due to the competition between the transportation and diffusion of precursor molecules onto the substrate surface and the reaction consumption of precursor atoms on the substrate surface. In addition, it is also observed that the lateral size of Bi2Te3 nanoplates decreases with increasing the total inner tube pressure as a result of the reduced diffusion rate of Bi2Te3 precursor molecules. 2D Bi2Te3 nanoplates with a lateral size over 10 μm can be obtained with applying proper precursor material temperature and total inner tube pressure. Furthermore, a visible photodetector is fabricated using few-layered 2D Bi2Te3 nanoplates grown in this work. This visible photodetector demonstrates a high responsivity of 23.43 AW−1 and a high detectivity of 1.54 × 1010 Jones, outperforming some visible detectors based on traditional 2D nanomaterials. Tche intensity-dependent photo-responsivity measurements show stable photoswitching behavior. This 2D Bi2Te3 nanoplate photodetector also presents high flexibility by showing no obvious performance degradation after being bent for 50 times. The results presented in this work will not only contribute to a comprehensive understanding of the CVD growth mechanism of Bi2Te3 nanostructures, but open up novel optoelectronic device applications for 2D Bi2Te3 nanostructures.

Improvement of photovoltaic properties of n-Cu2O/Au Schottky junctions

Development of Schottky junctions made with extremely cheap semiconductor material of electrodeposited cuprous oxide (Cu2O) is a viable approach for the low cost solar energy applications. In this study, Cu2O/Au Schottky junctions were investigated for this purpose. Two pre-treatment processes annealing in air at 175 °C for 15 min duration and sulphidation of film surfaces with ammonium sulphide vapour at 27 °C for 8 s duration were investigated. The study was also extended to combine pre-treatment of first annealing in air followed by sulphidation. Schottky junctions were fabricated by sputtering Au films of thickness ∼12 nm on pre-treated films. XRD, SEM, capacitance-voltage, current-voltage and photoresponse measurements were employed in the investigation. The unique pre-treatment process of combine annealing and sulphidation of n-Cu2O films resulted a Schottky junction capable of producing an increase in the built-in voltage from −197 mV to −943 mV at the interface and to record a high short circuit current density of 10.52 mA cm−2. In general, all the pre-treatment had a positive effect on the junction performance. Efficiency of the device is still at the low side (0.63%) due to poor fill factor and open circuit voltage. The study demonstrated that further optimization of pre-treatment processes and improvement of other structural parameters could produce an n-Cu2O/Au Schottky junction cable of producing conversion efficiency suitable for large scale solar energy applications.

Electrical and optical properties of photodiode structures formed by surface polymerization of [P (EGDMA-VPCA)-SWCNT] films on n-GaAs

Poly (ethylene glycol dimethacrylate-1-vinyl-1H-pyrrole-2-carboxylic acid)/carbon nanotube, single-walled)/n-GaAs ([P (EGDMA-VPCA)-SWCNT]/n-GaAs) photodiode structures were fabricated by using surface polymerization method. Electrical and optical properties were measured at several temperatures. Dark and light current characteristics were investigated. Spectral photoresponse measurements of the structure were made at room temperature. The maximum open circuit voltage (Voc) and short-circuit current (Isc) values for the diode under 20 mW/cm2 were obtained to be 0.52 V and 54.63 μA respectively. That showed that the fabricated structure exhibited rectification behavior that makes it a good candidate for optoelectronic device applications.

Ferroelectric, Photoelectric, and Photovoltaic Performance of Silver Niobate Ceramics

AbstractFerroelectrics coupled with solar energy conversion are receiving intensive research interest. However, most ferroelectrics with a large remnant polarization can only harvest ultraviolet light in the solar spectrum. Herein, high‐quality silver niobate (AgNbO3) ceramics prepared by spark plasma sintering is reported with a bandgap of ≈2.75 eV and a long tail absorption until 800 nm, leading to outstanding photoelectric properties featured by the visible‐light response over 550 nm. Instantaneous photoresponse measurement using a 355 nm nanosecond pulse laser shows a fast response speed in nanoseconds. Moreover, the ceramic exhibits an intriguing photovoltaic effect under either electric poling or mechanical polishing. Both approaches have switchable characteristics and produce a stable photovoltage as well as photocurrent, while temperature dependence behavior reveals distinctions between ferroelectric polarization and ferroelastic strains in determining the photovoltaic properties. Piezoelectric force microscopy characterization further confirms distinctions between the underlying mechanisms. The electric poling induced photovoltaic effect stems from the aligned polarization involving the ferroelectric component, whereas the mechanical polishing induced photovoltaic effect is associated with the flexoelectricity induced by strain gradients. These results not only show AgNbO3 to be a promising material for photoelectric application but also deepen the understanding of the mechanism underlying ferroelectric photovoltaics.

Self-powered room temperature broadband infrared photodetector based on MoSe2/germanium heterojunction with 35 A/W responsivity at 1550 nm

A highly efficient room temperature photodetector with broadband (400 nm–1800 nm) photoresponse based on the MoSe2/Ge heterojunction has been reported here. The fabricated MoSe2/Ge heterojunction exhibits high responsivity up to 24 A/W in the near-infrared wavelength range (750 nm) and 35 A/W in the short wavelength infrared range (1550 nm). The interfacial charge transfer at the Ge-MoSe2 heterojunction enables self-powered photo-detection in fabricated devices with zero bias responsivity values of 250 mA/W (750 nm) and 400 mA/W (1550 nm). Transient photoresponse measurements of the MoSe2/Ge heterojunction under the modulated light reveal that the devices are capable of working up to 20 kHz with a fast rise/fall time of 13.5/1.2 μsec. These results demonstrate the feasibility of achieving a high-performance photodetector derived from the MoSe2/Ge heterojunction for broadband infrared detection.

A PEC Sensor Based on Graphene Modified Platinum/N-Silicon Electrode for Sensing of Hydroquinone and Catechol

A graphene (Gr) decorated platinum/n-silicon (Pt/Si) sensor was put forward to detect hydroquinone (HQ) and catechol (CC) in a photoelectron chemical (PEC) way. Platinum film was coated on the polished side of the n-silicon wafer by vacuum evaporation and then Hummer method prepared graphene was used to decorate the Pt/Si wafer to build a Gr-Pt/Si PEC sensor. The morphology of the Gr-Pt/Si was characterized by SEM and the modified graphene was characterized by FTIR. The photoelectric properties of the Gr-Pt/Si were studied by semi-log current-voltage (logI–V) and photo response measurements. The suggested sensor was used to detect HQ and CC in a linear range of 10-300 μM with a detection limit of 1.9μMand 2.4 μM(S/N=3), respectively.

An efficient wide range photodetector fabricated using a bilayer Bi2S3/SnS heterojunction thin film

This study presents a detailed optoelectronic investigation on the bilayer Bi2S3/SnS heterojunction photodetector. The Bi2S3 and SnS nanostructures were synthesized by an ultrasonication method and deposited in the form of thin films by a thermal evaporation system to fabricate the photodetectors. The performed optoelectrical measurements showed that the Bi2S3 and Bi2S3/SnS photodetectors are respectively n- and p-type electrical conductivity. This finding was further confirmed by current–voltage (I–V) analysis, Mott–Schottky plots and photoresponse measurements. According to the obtained gain and sensitivity values, the Bi2S3/SnS heterojunction provides a higher photon-to-electrical carrier conversion relative to the Bi2S3 photodetectord due to the enhanced photogeneration of electron–hole pairs and separation of the photoinduced charge carriers under the influence of the electric field build-in at the heterojunction’s interface. The heterojunction exhibited a remarkable photoresponse from 400 to 800 nm by giving the photocurrent gain (G), sensitivity (S), and external quantum efficiency (EQE) values of 8460%, 450% and 45%, respectively. The obtained results represent the Bi2S3/SnS heterojunction photodetector as a potential candidate for devising high-performance optoelectronic devices.

Fabrication of p-NiO nanoflakes/n-Si(100) heterojunction architecture for high sensitive photodetectors

We report the facile hydrothermal synthesis of p-NiO nanoflakes (NFs)/n-Si (100) heterojunction architecture and its photoresponse behavior. The vertically grown NiO NFs architecture is clearly seen on the Si substrate, as evidenced from the field emission scanning electron microscopy images. The elemental composition of the grown nanostructure on the Si substrate was estimated using energy-dispersive X-ray spectroscopy, and resonant Rutherford backscattering spectrometry measurements. The grazing incidence X-ray diffraction measurement reveals the grown NiO NFs architecture is of face centered cubic phase. The I-V characteristics of p-NiO NFs/n-Si heterojunction architecture shows good rectifying behavior in the dark and the increased photocurrent in the reverse bias imply the formation of p–n junction at the interface of p-NiO NFs and n-Si substrate. The voltage-dependent sensitivity of the device reveals the highest sensitivity at reverse bias of 3 V. The time-dependent photoresponse measurements of the device show good stability and repeatability under blue light illumination. The response and recovery time of the device is found as 6.18 s and 1.83 s under the reverse bias of 3 V. Our experimental studies demonstrate that the fabricated p-NiO NFs/n-Si heterojunction device has considerable promise for the practical photodetector applications.

Effect of Immersion Cycle on Photoelectrochemical Properties of Cu2O Thin Films on Stainless Steel Substrate Prepared by Chemical Bath Deposition Method

Cu2O is a semiconductor that has a band gap 2.2 eV and potentially used as working electrode of PEC cell. Cu2O thin layer is synthesized by chemical bath deposition (CBD) method at the room temperature. The formation of Cu2O thin layer was prepared on a stainless steel substrate. In this work, we investigate the effect of a Cu2O thin layer/stainless steel as a working electrode with immersion cycle variation. The crystal structure was analyzed by XRD. Photoresponse measurement has time response τr of 1.3 s andtime decay τdof 2.9 s with the maximum current of 40 nA.