Photoelectronic Devices Research Articles

Electronic and transport properties of GaAs/InSe van der Waals heterostructure

Recently, the GaAs/InSe heterostructure was synthesized experimentally, and the spatial redistribution of charge and motion of energy-resolved photoelectron was imaged. To gain more insight into the detailed electronic structure and expand knowledge to transport behaviors and physical field tuning effects, we here construct the GaAs/InSe van der Waals heterostructure theoretically and perform investigations in depth, especially focusing on the comprehensive understanding and mechanism analysis of results, trying to create new predictions. The results show that such a heterostructure holds a typical type-II band alignment and its band gap is narrowed significantly as compared with its each component, and the indirect-direct band gap transition is realized, which holds great potential applications in developing excellent photovoltaic materials and new photo-electronic devices. Particularly, the carrier mobility of heterostructure is predicted to be enhanced dramatically to μ > 104 cm2 V−1 s−1, greatly overcoming the intrinsic weakness of InSe monolayer with a very low hole mobility, ~101 cm2 V−1 s−1. Meanwhile, we find that the electronic structure of the heterostructure is flexibly controllable. Under higher compressive strain and whole tensile strain, its band-gap size drops linearly. While by applying an external electric field, the band offset is increased significantly, and the type-II band alignment is well preserved and the band gap drops significantly under positive external electric field, These flexibly tunable properties are more favorable to design the photovoltaic materials and photo-electronic devices.

Photophysics of 2D Organic-Inorganic Hybrid Lead Halide Perovskites: Progress, Debates, and Challenges.

2D organic–inorganic hybrid Ruddlesden–Popper perovskites (RPPs) have recently attracted increasing attention due to their excellent environmental stability, high degree of electronic tunability, and natural multiquantum‐well structures. Although there is a rapid development of photoelectronic applications in solar cells, photodetectors, light emitting diodes (LEDs), and lasers based on 2D RPPs, the state‐of‐the‐art performance is far inferior to that of the existing devices because of the limited understanding on fundamental physics, especially special photophysics in carrier dynamics, excitonic fine structures, excitonic quasiparticles, and spin‐related effect. Thus, there is still plenty of room to improve the performances of photoelectronic devices based on 2D RPPs by enhancing knowledge on fundamental photophysics. This review highlights the special photophysics of 2D RPPs that is fundamentally different from the conventional 3D congeners. It also provides the most recent progress, debates, challenges, prospects, and in‐depth understanding of photophysics in 2D perovskites, which is significant for not only boosting performance of solar cells, LEDs, photodetectors, but also future development of applications in lasers, spintronics, quantum information, and integrated photonic chips.

Artificial Photosynthesis: Is Computation Ready for the Challenge Ahead?

A tremendous effort is currently devoted to the generation of novel hybrid materials with enhanced electronic properties for the creation of artificial photosynthetic systems. This compelling and challenging problem is well-defined from an experimental point of view, as the design of such materials relies on combining organic materials or metals with biological systems like light harvesting and redox-active proteins. Such hybrid systems can be used, e.g., as bio-sensors, bio-fuel cells, biohybrid photoelectrochemical cells, and nanostructured photoelectronic devices. Despite these efforts, the main bottleneck is the formation of efficient interfaces between the biological and the organic/metal counterparts for efficient electron transfer (ET). It is within this aspect that computation can make the difference and improve the current understanding of the mechanisms underneath the interface formation and the charge transfer efficiency. Yet, the systems considered (i.e., light harvesting protein, self-assembly monolayer and surface assembly) are more and more complex, reaching (and often passing) the limit of current computation power. In this review, recent developments in computational methods for studying complex interfaces for artificial photosynthesis will be provided and selected cases discussed, to assess the inherent ability of computation to leave a mark in this field of research.

Centimeter‐Sized Single Crystals of Two‐Dimensional Hybrid Iodide Double Perovskite (4,4‐Difluoropiperidinium)4AgBiI8 for High‐Temperature Ferroelectricity and Efficient X‐Ray Detection

AbstractFerroelectricity and X‐ray detection property have been recently implemented for the first time in hybrid bromide double perovskites. It sheds a light on achieving photosensitive and ferroelectric multifunctional materials based on 2D lead‐free hybrid halide double perovskites. However, the low Tc, small Ps, and relatively low X‐ray sensitivity in the reported bromide double perovskites hinder practical applications. Herein, the authors demonstrate a novel 2D lead‐free iodide double perovskite (4,4‐difluoropiperidinium)4AgBiI8 (1) for high‐performance X‐ray sensitive ferroelectric devices. Centimeter‐sized single crystal of 1 is obtained and exhibits an excellent ferroelectricity including a high Tc up to 422 K and a large Ps of 10.5 μC cm−2. Moreover, due to a large X‐ray attenuation and efficient charge carrier mobility (μ)–charge carrier lifetime (τ) product, the crystal 1 also exhibits promising X‐ray response with a high sensitivity up to 188 μC·Gyair−1 cm−2 and a detection limit below 3.13 μGyair·s−1. Therefore, this finding is a step further toward practical applications of lead‐free halide perovskite in high‐performance photoelectronic devices. It will afford a promising platform for exploring novel photosensitive ferroelectric multifunctional materials based on lead‐free double perovskites.

Applications of Few-Layer Nb2C MXene: Narrow-Band Photodetectors and Femtosecond Mode-Locked Fiber Lasers.

Although the physicochemical properties of niobium carbide (Nb2C) have been widely investigated, their exploration in the field of photoelectronics is still at the infancy stage with many potential applications that remain to be exploited. Hence, it is demonstrated here that few-layer Nb2C MXene can serve as an excellent building block for both photoelectrochemical-type photodetectors (PDs) and mode-lockers. We show that the photoresponse performance can be readily adjusted by external conditions and that Nb2C NSs exhibit a great potential for narrow-band PDs. The demonstrated mechanism was further confirmed by work functions predicted by density functional theory calculations. In addition, as an optical switch for passively mode-locked fiber lasers, ultrastable pulses can be demonstrated in the telecommunication and mid-infrared regions for Nb2C MXene, and as high as the 69th harmonic order with 411 MHz at the center wavelength of 1882 nm can be achieved. These intriguing results indicate that few-layer Nb2C nanosheets can be used as building blocks for various photoelectronic devices, further broadening the application prospects of two-dimensional MXenes.

Improved photovoltage of printable perovskite solar cells via Nb5+ doped SnO2 compact layer

The state-of-the-art perovskite solar cells (PSCs) with SnO2 electron transporting material (ETL) layer displays the probability of conquering the low electron mobility and serious leakage current loss of the TiO2 ETL layer in photoelectronic devices. The rapid development of SnO2 ETL layer has brought perovskite efficiencies >20%. However, high density of defect states and voltage loss of high temperature SnO2 are still latent impediment for the long-term stability and hysteresis effect of photovoltaics. Herein, Nb5+ doped SnO2 with deeper energy level is utilized as a compact ETL for printable mesoscopic PSCs. It promotes carrier concentration increase caused by n-type doping, assists Fermi energy level and conduction band minimum to move the deeper energy level, and significantly reduces interface carrier recombination, thus increasing the photovoltage of the device. As a result, the use of Nb5+ doped SnO2 brings high photovoltage of 0.92 V, which is 40 mV higher than that of 0.88 V for device based on SnO2 compact layer. The resulting PSCs displays outstanding efficiency of 13.53%, which contains an ∼10% improvements compared to those without Nb5+ doping. Our study emphasizes the significance of element doping for compact layer and lays the groundwork for high efficiency PSCs.

Bell-Shaped Electron Transfer Kinetics in Gold Nanoclusters.

Although metal nanoclusters (MNCs) have shown great promise for the further development of photochemical techniques to be applied in diverse areas (e.g., photoelectronic devices, photochemical sensors, photocatalysts, and energy storage and conversion systems), the fundamental problem of their electron transfer behavior still remains unsolved. Herein, a driving force-dependent photoinduced electron transfer process of gold nanoclusters (AuNCs) is clarified for the first time from a rational-designed opposite-charged system. It was found that the electron transfer dynamic of carboxylated chitosan and dithiothreitol-commodified AuNCs (CC/DTT-AuNCs) can be satisfactorily described by the Marcus electron transfer theory. This proved model was applied to estimate the ultrafast charge separation process between CC/DTT-AuNCs and mitoxantrone, which was confirmed by fluorescence quenching and femtosecond transient absorption spectroscopy measurements. We envision that this work will open a new door for understanding the electron transfer behavior of MNCs and facilitate the design of advanced optoelectronic devices.

A reliable and accurate model of photoelectron yield spectrum and its applications

Experimental and theoretical research on photoelectron yield spectrum play a crucial role in electronic and photo-electronic materials and devices, and the reliable and precise estimation of photoelectron yield via photon energy is very important for detecting microscopic electrical information in photo-electronic materials and devices. Photoelectron yield is defined as the number of electrons emitted by per incident photon. Before this work, the technique was based on the interception of a plot of square root of photoelectron yield versus photon energy for metal-insulator hetero-junction, and that of a plot of cube root of photoelectron yield variation with photon energy for insulator-semiconductor hetero-junction. But, how to intercept the relationship between photoelectron yield and photon energy for semiconductor-semiconductor and metal-semiconductor hetero-junctions has not been known. Besides, many experimental plots of square root and cube root of photoelectron yield against photon energy are available, but none of them is a straight line. In order to obtain a more accurate and reliable barrier height, electrical structure of the junction, the energy level distribution of the energy band offset, defect density in the junction, and the valence band profile through the photoelectric yield spectrum, a reliable and accurate model of photoelectron yield spectrum is established via combining the solution to a differential equation and experimental results. A method is proposed to naturally determine the junction barrier height by using the experimental results of the internal current yield varying with the photon energy. The this method can be used to calculate the junction barrier height as accurately and reliably as possible, and the density and energy level distributions of the effective occupancy states of the electrons in the four junctions are obtained by using this photoelectric yield spectrum model, In addition, based on this model, this paper proves mathematically that the density and energy level distribution of the effective occupancy state of electrons present a peak shape. Therefore, the application prospects of this photoelectric yield spectrum model are demonstrated.

Vertically stacked GaN/WX2 (X = S, Se, Te) heterostructures for photocatalysts and photoelectronic devices.

Tremendous attention has been paid to vertically stacked heterostructures owing to their tunable electronic structures and outstanding optical properties. In this work, we explore the structural, electronic and optical properties of vertically stacked GaN/WX2 (X = S, Se, Te) heterostructures using density functional theory. We find that these stacking heterostructures are all semiconductors with direct band gaps of 1.473 eV (GaN/WTe2), 2.102 eV (GaN/WSe2) and 1.993 eV (GaN/WS2). Interestingly, the GaN/WS2 heterostructure exhibits a type-II band alignment, while the other two stackings of GaN/WSe2 and GaN/WTe2 heterostructures have type-I band alignment. The optical absorption of GaN/WX2 heterostructures is very efficient in the visible light spectrum. Our results suggest that GaN/WX2 heterostructures are promising candidates for photocatalytic water splitting and photoelectronic devices in visible light.

First-principles study of electronic structure and optical properties of monolayer defective tellurene

Monolayer tellurene is a novel two-dimensional semiconductor with excellent intrinsic properties. It is helpful in understanding doping and scattering mechanism to study the electronic structure of defective tellurene, thus it is important for the application of tellurene in electronic and photo-electronic devices. Using first-principles calculation based on the density functional theory, we investigate the effects of commonly seen point defects on the electronic structure and optical properties of monolayer <i>β</i>-Te. Seven kinds of point defects that may be present in <i>β</i>-Te are designed according to the lattice symmetry, including two single vacancies (SV-1, SV-2), two double vacancies (DV-1, DV-2) and three Stone-Wales (SW) defects (SW-1, SW-2, SW-3). It is found that the defect formation energies of these defects are 0.83–2.06 eV, which are lower than that in graphene, silicene, phosphorene and arsenene, suggesting that they are easy to introduce into monolayer <i>β</i>-Te. The two most stable defects are SV-2 and SW-1 where no dangling bond emerges after optimization. The calculated band structures show that all seven defects have little effect on the band gap width of monolayer <i>β</i>-Te, but they can introduce different numbers of impurity energy levels into the forbidden band. Among them, the SV-1, SV-2, DV-1 and SW-2 each act as deep level impurities which can be recombination centers and scattering centers of carriers, SW-1 acts as a shallow level impurity, DV-2 and SW-3 act as both deep level impurity and shallow level impurity. Besides, SW-1, SW-2 and DV-1 can change the band gap of monolayer <i>β</i>-Te from direct band gap to indirect band gap, which may result in the increase of the lifetime of carriers and decrease of photoluminescence of monolayer <i>β</i>-Te. The optical properties of monolayer <i>β</i>-Te, which are sensitive to the change in band structure, are also affected by the presence of defects. New peaks are found in the complex dielectric function and the absorption coefficient of defective monolayer <i>β</i>-Te in an energy range of 0–3 eV, of which the number and the position are dependent on the type of defect. The SV-1, DV-1, DV-2 and SW-2 can enhance the light response, polarization ability and light absorption in the low energy region of monolayer <i>β</i>-Te. This research can provide useful guidance for the applications of <i>β</i>-Te in the electronic and optoelectronic devices.

Кремнієвий p–i–n-фотодіод із підвищеною імпульсною чутливістю

P-n junction semiconductor photodetectors are widely used in various fields of science and technology, including automation and telecontrol, instrumentation equipment, tracking systems, guidance, etc. The most demanded photoelectronic devices are silicon p-i-n photodiodes (PD). Their main field of application are installations using laser beams of near IR optical radiation spectrum, λ = 1060 nm, in particular. The article provides considerations and limit requirements for production of high-responsivity silicon p-i-n photodiodes and making theoretical parameters consistent with real photodiodes made according to the design. Characteristic properties of technology, construction and final parameters of the manufactured four-element segment p–i–n photodiode with a guard ring are described. The authors describe the criteria for choosing the material for making high-responsivity photodiodes. Results of the theoretical design for the capacitance of the photodiode based on the materials of different resistivity are presented. A theoretically possible value for the dark current of the responsive elements and the guard ring is considered for the silicon of 18 kOhm•cm. Criteria for the thickness of the PD crystal and the doped areas that provide for the maximum width of the space-charge region are presented. The dependence of the current pulse monochromatic responsivity from the operating voltage of the photodiode is shown for substrates with different thickness. The photodiodes obtained during this study have the pulse monochromatic responsivity of 0.48 A/W, which is higher than that of commercial products of well-known foreign manufacturers. The results achieved demonstrate that this technology is effective and the assumptions made during the calculation stage are valid.

Nonlinear Optics in Lead Halide Perovskites: Mechanisms and Applications

Because of their unique and excellent photophysical properties, lead halide perovskites are widely used in photoelectronic devices such as photodetectors, light-emitting diodes, solar cells, and la...

Lead Sulfide Quantum Dots Mode Locked, Wavelength-Tunable Soliton Fiber Laser

We fabricate an oleic acid capped colloidal lead sulfide quantum dots (PbS QDs) by modified hot-injection method, and then drop them on the end of fiber connector to construct the fiber-based PbS QDs saturable absorber (SA). The modulation depth and saturation intensity of the PbS QDs SA are about 30% and 1.88 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The strong quantum confinement effect in PbS QDs enables wideband tunability. We get subpicosecond soliton pulses, wavelength-tunable between 1530 nm and 1560 nm, with stable mode-locking, by adjusting the orientations of the polarization controller. These results contribute to study the nonlinear optical properties of zero-dimensional nanomaterials and provide new opportunities for the applications of broadband photoelectronic devices.

Investigation of the electronic structure of two-dimensional GaN/Zr2CO2 hetero-junction: Type-II band alignment with tunable bandgap

By applying first-principles calculations, we construct the GaN/Zr2CO2 hetero-junction and explore its electronic structure properties. Band structure calculations indicate that GaN/Zr2CO2 junction possesses type-II band alignment. The valence band maximum (VBM) is dominated by GaN and the conduction band minimum (CBM) dominated by Zr2CO2. The large binding energy and short inter-layer spacing distance suggest that there exists chemical adsorption between the two layers beyond van der Waals (vdW) interaction. Furthermore, large conduction band offset (CBO) (2.70 eV) and powerful built-in electric field (2.34 eV) indicate that the GaN/Zr2CO2 hetero-junction may be an excellent candidate for the photo-electronic device or photocatalyst applications. We also investigated the influence of biaxial strain on the band structure of GaN/Zr2CO2. The bandgap of the GaN/Zr2CO2 hetero-junction can be tailored by biaxial strain effectively. Especially, the bandgap closes up at the compressive strain of −5%, Our calculations demonstrate that the GaN/Zr2CO2 hetero-junction is promising for tunable high-performance optoelectronic nanodevices.

Flexible and high-performance broadband nanoflowers tin sulfide photodetector

A significant prerequisite for the development of a high-performance photodetector remains its low dark current value, because it promotes sensitivity and signal-to-noise ratio, in addition to low detectability light power density. Nevertheless, the fabricated photodetectors, which are based on deposited tin sulfide (SnS) films onto a flexible (PET at pH 5) and glass substrates, exhibited relatively high dark current values around (0.2 µA) and (several µA), respectively. This study proposes a novel approach for a better control of the photoresponse characteristics of nanostructured SnS film which resulted from reducing the deposition growth rate by adjusting the pH of the reaction solution to 5.8. The film was deposited onto a flexible substrate of polyethylene terephthalate (PET) using an inexpensive chemical bath deposition method. The as-fabricated photodetector exhibited a low dark current value approximately (~ 24 nA) at 5 V bias voltage and a good response in a broad range covering the UV up to the near-infrared. Besides, light-emitting diodes (380, 530, 750, and 850 nm) were used to investigate the photoresponse characteristics of the photodetector. The latter manifested fast photoresponse times (rise and decay) and good sensitivity for all used illumination wavelengths. Furthermore, under various illumination power densities of 850 nm, the photocurrent manifested a good dependence upon power density. Based on the obtained excellent photoresponse characteristics, this photodetector is promising for the photoelectronic flexible device in the UV–Vis–NIR range.

Development of High Performance C-Rich a-SiC Semiconductors with Narrow-Optical Gap By Control of Its Phase Structure

1. Introduction For the expansion of application fields (ex. tailor-made photocatalysts and high-efficiency laser) of semiconductor, novel semiconductor materials with variable optical gaps in the range from 1.2 to 3.0 eV is necessary to be developed. The promising candidate of these semiconductor is carbon-rich amorphous silicon-carbon alloy (C-rich a-SiC).[1] The optical gaps (Eog) of C-rich a-SiC can be changed from 1.2 to 2.7 eV by changing the Si/C ratio. Hetero-junction solar cell comprising N-doped C-rich a-SiC with Eog = 2.7 eV and p-type Si have been reported to show the function of photon to electron conversion.[2] However, solar cells comprising N-doped C-rich a-SiC with Eog from 1.2 to 1.7 eV showed extremely lower conversion efficiencies. Therefore, all of these C-rich a-SiC with Eog from 1.2 to 2.7 eV may not be applied to photoelectronic devices. The objective of this study is to realize C-rich a-SiC with lower Eog (frim 1.2 to 1.7 eV) that have higher semiconductor property and are able to be applied to photoelectronic devices. a-SiC has a multiphase structure in which amorphous Si-C network (Si:C = x:1-x), sp2-hybridized carbon cluster (sp 2 clusters), and silicon-like clusters (Si-cluster) coexist. It has been reported that excess sp2 cluster worked as a recombination center of photoexcited carries. It results in the degradation of efficiencies of photon to electron conversion. In order to realize C-rich a-SiC with lower Eog and higher photon to electron conversion efficiency, the synthesis method that can enhance of ratio of C/Si in amorphous Si-C network and suppress the formation of sp 2 clusters in C-rich a-SiC is necessary to be developed. In this study, CVD synthesis using high-frequency and lower power r. f. plasma was tried to be adopted to induce two types of structural change at C-rich a-SiC. High-frequency and lower power r. f. plasma can avoid the formation of sp 2 clusters in C-rich a-SiC. It results in the semiconductor materials with lower Eog and higher photon to electron conversion efficiency.2. Experimental Nitrogen-doped C-rich a-SiC thin films were synthesized by radio frequency plasma enhanced chemical vapor deposition system (RF-PeCVD) (13.56 MHz, SAMCO Co., Ltd. Model BPD-1) using tetramethylsilane, 1,1,3,3-tetrametyldisilazane and n-hexanes as source materials. C-rich a-SiC thin films were deposited on glass plate and boron-doped silicon (100) substrate (resistivity of 2 W cm) after an in-situ sputter cleaning with argon ions. Substrate temperature was kept at 160 degree C during CVD deposition. The frequency of r.f. power supply was set at 60 MHz and r.f power were changed from 5 to 26 W. The deposition time was 80 minutes. Transmission spectra of N-doped C-rich a-SiC deposited on glass substrates were examined by UV-Vis spectrophotometer (JASCO Co., Ltd. V-670). The performance of heterojunction solar cells was investigated by current-voltage (I-V) measurement (KEYSIGHT, B2901A) with simulated AM 1.5 sunlight (ASAHI SPECTRA, HAL-320). 3. Results and Discussion Eog estimated from transmission spectra (Fig. 1) of resulting N-doped C-rich a-SiC were found to be in the range from 1.40 to 2.96 eV, as shown in Table 1. Eog was able to be controlled to lower value (1.4 eV) thorough the change of the S/C ratios in C-rich a-SiC (by changing the volume ratio of n-hexane in source materials). All hetero-junction solar cells comprising N-doped C-rich a-SiC with various Eog and p-type Si crystal were confirmed to show the function of photon-to electron conversion (Table 1). The improvement of function of photon to electron conversion at C-rich a-SiC with lower Eog (ca. 1.4 eV) might be caused by the suppression of the recombination of photo-exited electrons and holes. In Figure 1, the absorption peak of sp 2 clusters was observed at 1.1 eV and was clearly separated from the absorption peak of amorphous Si-C network (observed at 2.6 eV). The intensity decrease and peak shift to lower energy side of the absorption of sp 2 clusters in Fig. 1 indicates the decrease of the amount of sp 2 clusters and the enlargement of size of sp 2 clusters. These structural change might cause the suppression of recombination of photo-carriers. The relation between Eog and open circuit voltage of solar cell was consistent with estimated value from electronic structure of C-rich a-SiC. It was summarized that the development of C-rich a-SiC semiconductors with lower Eog (in the range from 1.4 to 1.7 eV) that are able to be applied to photo-electronic devices was successfully achieved. 4.

Back contact modification of the optoelectronic device with transition metal dichalcogenide VSe2 film drives solar cell efficiency

VSe2 is with high electrical conductivity and high work function, thus it is beneficial for the carrier transport in the optoelectronic devices. However, the performance and mechanism of its effect on the photoelectronic devices conversion efficiency is still beyond understood. In this work, we fabricate VSe2 film between back contact and absorber layer Cu2ZnSn(S,Se)4 (CZTSSe) film. We demonstrate that the VSe2 film in back contact region increases solar cell efficiency by 39%. Besides improving the carrier transport in the back contact region, the increasing can also be attributed to the reduction of the decomposition reaction of CZTSSe during the nucleation of CZTSSe as VSe2 fabricated between back contact and absorber layer. The present work not only provides an effective method to improve the performance of the optoelectronic device, but also shows an attractive application of metallic TMDs in optoelectronic device and solar cell energy generation.

Tuning the Work Function of the Metal Back Contact toward Efficient Cu2ZnSnSe4 Solar Cells

Carrier collection is crucial for thin film photoelectronic devices. As photoelectronic devices, the undesirable energy band structure between the metal contact and p‐type absorber is a serious limitation to boost the open‐circuit voltage (VOC) of thin film solar cells. Herein, the carrier collection near the back contact of a kesterite solar cell is promoted by tailoring the work function of the back contact. By diffusing P into Mo back contact of the kesterite solar cell, the work function of the Mo back contact is increased from 4.68 to 5.62 eV and the diffused P bonds with Mo as anions, thus resulting in the energy band bending upward at the back interface and enabling the fluent transmission of holes. The efficiency of Cu2ZnSnSe4 solar cells increases from 6.8% to 11.28%. The results expand the path to improving carrier collection in solar cells and electronic devices utilizing metal film contacts.

A fresh-bias photoresponse of graphene field-effect transistor: An electrical tunable fast dipole moment generation

A unique extra photoresponse of graphene field-effect transistor to the first laser pulse after a switch of back-gate voltage (VBG) is reported and explored here. It is referred as fresh-bias photoresponse (FBPR). FBPR suggests a unique prompt charge transfer process triggered by laser illumination with the help of the VBG and the transferred charge holds as far as the VBG holds unchanged. The responsible charge transfer process is proposed between ester oxygen and carbonyl carbon atoms in the ester side chains of poly(methyl methacrylate) (PMMA) molecule. The proposed mechanism explains perfectly all of the features of FBPR. The charge transfer process generates an inter-molecular dipole moment of PMMA. Such dipole moment generation is much fast than that introduced by a photo-triggered isomerization reaction of photochromic molecule, which have been used in graphene based photodetectors. This mechanism is further confirmed by the test result of a control device with mechanically exfoliated graphene channel and a control device fabricated on hexagonal boron nitride substrate. The mechanism behind FBPR may provide a new way of developing phototransistors, photodetectors or photoelectronic memory devices in the future.

Direct ion-beam deposition of Ag nanoparticles using a solid-state silver ion source

Ion beam technology has shown itself worth to be an efficient method to produce nanoparticles embedded in dielectrics for photoelectronic devices. However, direct ion-beam deposition of nanoparticles (NPs) on the surface of dielectrics is rarely reported because the conventional metal ion source runs into difficulties to generate low energy (<10 keV) ion-beams. Herein, Ag NPs are directly deposited on the surface of Si substrates using the recently developed solid electrolyte ion source (SEIS), which possesses advantages of compactness, simple working conditions, and ability of emitting ion-beam at an energy of few keV. The composition, morphology and size of the synthesized Ag NPs are studied. Precise control of the NPs size including in-plane diameter and height is achieved by a modulation of the ion implantation dose. Localized maskless deposition of metal films on semiconductor surface is also expected using the SEIS device.