High-performance Phototransistors Research Articles

Ultra-thin two-dimensional molecular crystals grown on a liquid surface for high-performance phototransistors.

A novel strategy for the growth of molecularly thin two-dimensional molecular crystals (2DMCs) of organic semiconductors with poor solubility was developed. Large-area bilayer 2DMCs were grown on a liquid surface at elevated temperatures, with record mobility and superior photoresponse.

High-Performance Vertical Organic Phototransistors Enhanced by Ferroelectrics

Organic phototransistors with high sensitivity and responsivity to light irradiance have great potential applications in national defense, meteorology, industrial manufacturing, and medical security. However, undesired dark current and photoresponsivity limit their practical applications. Here, a novel vertical organic phototransistor combined with ferroelectric materials is developed. The device structure has nanometer channel length, which can effectively separate photogenerated carriers and reduce the probability of carrier recombination and defect scattering, thus improving the device performance of phototransistors. Moreover, by inserting the poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) ferroelectric layer, the Schottky barrier at the interface between the semiconductor and source can be adjusted by the polarization of the external electric field, which can effectively reduce the dark current of the phototransistor to further improve the device performance. Therefore, our phototransistors exhibit a high photoresponsivity of more than 5.7 × 105A/W, an outstanding detectivity of 1.15 × 1018 Jones, and an excellent photosensitivity of 5 × 107 under 760 nm light illumination, which are better than those of conventional lateral organic phototransistors. This work provides a new approach for the development of high-performance phototransistors, which opens a new pathway for organic phototransistors in practical application.

Light-modulated vertical heterojunction phototransistors with distinct logical photocurrents

The intriguing carrier dynamics in graphene heterojunctions have stimulated great interest in modulating the optoelectronic features to realize high-performance photodetectors. However, for most phototransistors, the photoresponse characteristics are modulated with an electrical gate or a static field. In this paper, we demonstrate a graphene/C60/pentacene vertical phototransistor to tune both the photoresponse time and photocurrent based on light modulation. By exploiting the power-dependent multiple states of the photocurrent, remarkable logical photocurrent switching under infrared light modulation occurs in a thick C60 layer (11 nm) device, which implies competition of the photogenerated carriers between graphene/C60 and C60/pentacene. Meanwhile, we observe a complete positive-negative alternating process under continuous 405 nm irradiation. Furthermore, infrared light modulation of a thin C60 (5 nm) device results in a photoresponsivity improvement from 3425 A/W up to 7673 A/W, and we clearly probe the primary reason for the distinct modulation results between the 5 and 11 nm C60 devices. In addition, the tuneable bandwidth of the infrared response from 10 to 3 × 103 Hz under visible light modulation is explored. Such distinct types of optical modulation phenomena and logical photocurrent inversion characteristics pave the way for future tuneable logical photocurrent switching devices and high-performance phototransistors with vertical graphene heterojunction structures.

Superior phototransistors based on a single ZnO nanoparticle with high mobility and ultrafast response time

We show that devices containing a ZnO single particle exhibit mobility values one order higher than single-crystal nanowires and a record-high photoresponse rise time. This device could be an excellent candidate for high performance phototransistors.

High performance phototransistors with organic/quantum dot composite materials channels

Abstract Nanomaterials, especially quantum dots, have become one of the most great potential channel transport layer materials in the field of photo detection mainly due to their particular light absorption characteristics. However, there are still many disadvantages such as low carrier transport capability possibly attributable to the discontinuity nature of materials. Therefore, particular phototransistors with pentacene/CdSe@ZnS QDs composite materials channels have been prepared by simply blending and spin-coating 6,13-Bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) and QDs solution in weight ratio of 3:1. The particular device architecture with organic/quantum dot composite materials channels effectively combined the high carrier mobility advantage of organic semiconductors with the strong absorption characteristic of quantum dots in specific optical band regions and further overcame the low conductivity shortcomings of pure quantum dot materials. The device with particular pentacene/CdSe@ZnS QDs composite channel exhibited excellent electrical and optical properties with current switch ratio Ion/off of 104, carriers mobility of ~0.161 cm2/V, photosensitivity P of 105, responsivity R of 0.33 mA/W and detectivity D of 1.48 × 1011 Jones at drain voltage of −35 V and light intensity of 1.6 mW/cm2, respectively, indicating that this composite, as one of the most promising channel transport layer material candidates for photodetector, provides one chance to improve the characteristic of photodetector transistors just by using hybrid channel technology.

Deep-ultraviolet SnO2 nanowire phototransistors with an ultrahigh responsivity

The effect of interfacial charges between a semiconductor and a dielectric is absolutely crucial for high-performance phototransistors. In this paper, we report a novel deep-ultraviolet photodetector based on one-dimensional SnO2 nanowires (NWs) phototransistors with an ion-gel as the surrounding gate dielectric. The density of trapped carriers induced by light irradiation could be significantly amplified via the use of high-efficiency surrounding electrolyte coupling, thus, enhancing the photogating effect. The as-fabricated devices demonstrated an outstanding responsivity of 2 × 107 A/W under weak light illumination of 18.2 μW/cm2. Based on our systematic investigation of the threshold voltage shift and photodetection performance, we present a theoretical explanation for the high-performance SnO2 NWs phototransistors with the assistance of energy band analysis. The specific configuration and high-efficiency gating of the ion-gel electrolyte were particularly interesting from a photodetection point of view, providing new insights into the design and optimization of deep ultraviolet photodetection.

A gate-free MoS2 phototransistor assisted by ferroelectrics

During the past decades, transition metal dichalcogenides (TMDs) have received special focus for their unique properties in photoelectric detection. As one important member of TMDs, MoS2 has been made into photodetector purely or combined with other materials, such as graphene, ionic liquid, and ferroelectric materials. Here, we report a gate-free MoS2 phototransistor combined with organic ferroelectric material poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)). In this device, the remnant polarization field in P(VDF-TrFE) is obtained from the piezoelectric force microscope (PFM) probe with a positive or negative bias, which can turn the dipoles from disorder to be the same direction. Then, the MoS2 channel can be maintained at an accumulated state with downward polarization field modulation and a depleted state with upward polarization field modulation. Moreover, the P(VDF-TrFE) segregates MoS2 from oxygen and water molecules around surroundings, which enables a cleaner surface state. As a photodetector, an ultra-low dark current of 10–11 A, on/off ration of more than 104 and a fast photoresponse time of 120 μs are achieved. This work provides a new method to make high-performance phototransistors assisted by the ferroelectric domain which can operate without a gate electrode and demonstrates great potential for ultra-low power consumption applications.

Dual-Band, High-Performance Phototransistors from Hybrid Perovskite and Organic Crystal Array for Secure Communication Applications.

High-performance phototransistors made from organic semiconductor single crystals (OSSCs) have attracted much attention due to the high responsivity and solution-processing capability of OSSCs. However, OSSC-based phototransistors capable of dual-band spectral response remain a difficult challenge to achieve because organic semiconductors usually possess only narrow single-band absorption. Here, we report the fabrication of high-performance, dual-band phototransistors from a hybrid structure of a 2,7-dioctyl[1]benzothieno[3,2- b][1]benzothiophene (C8-BTBT) single-crystal array coated with CH3NH3PbI3 nanoparticles (NPs) synthesized by a simple, one-step solution method. In contrast to C8-BTBT and CH3NH3PbI3 NPs with respective absorption in the ultraviolet (UV) and visible (vis) region, their hybrid structure shows broad absorption covering the entire UV-vis range. The hybrid-based phototransistors exhibit an ultrahigh responsivity of >1.72 × 104 A/W in the 252-780 nm region, which represents the best performance for solution-processing, broadband photodetectors. Moreover, integrated phototransistor circuitries from the hybrid CH3NH3PbI3 NPs/C8-BTBT single-crystal array show applications for high-security communication.

Perovskite-WS2 Nanosheet Composite Optical Absorbers on Graphene as High-Performance Phototransistors.

High-responsivity phototransistors with a structure of perovskite-WS2 nanosheet composite optical absorber and a reduced graphene oxide (rGO) channel layer is demonstrated via a facile and low-cost solution-processing method. The WS2 nanosheets are dispersed within the perovskite matrix, forming the perovskite-WS2 bulk heterojunction (BHJ). The hybrid phototransistor exhibits excellent figures of merit including high photoresponsivity of 678.8 A/W, high specific detectivity of 4.99 × 1011 Jones, high EQE value of 2.04 × 105% and rapid response to photoswitching. The high photoresponsivity could be attributed to the WS2 nanosheets induced photo-generated electron-hole separation promotion effects due to the selective electron trapping effects in the WS2 nanosheets, together with the high carrier mobility of the rGO channel. This work provides a promising platform for constructing high-responsivity photodetectors.

High-Performance Organic Phototransistors With Vertical Structure Design

In this paper, a novel vertical phototransistor was reported and compared with planar phototransistors for the first time. As compared with the planar phototransistors, the vertical ones exhibited much better photoelectric performance, which is attributed to an ultrashort photo-generated holes transfer distance and a stronger excitons dissociating electrical field due to their ultrashort channel length (tens of nanometers). Moreover, in order to examine the transport and trapping of different carrier charges separately, the impact of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) dopant on the performance of planar and vertical phototransistors was investigated. The vertical devices exhibited an ultrahigh responsivity (~6600 A/W) as well as an excellent detectivity ( $\sim 7\times 10^{15}~\text{Jones}$ ) and a fast photoresponse (rise time of 0.28 s), whereas slight changes were observed in the planar ones with doping of PCBM. The high performance of the blend vertical phototransistors is due to the trapping of the photo-generated electrons with PCBM and the effective transport of holes due to the ultrashort channel length. This paper provided a promising pathway for low-cost, high-performance phototransistors.

Enhancement-mode CdS nanobelts field effect transistors and phototransistors with HfO2 passivation

As typical direct bandgap II–VI semiconductors, quasi-one dimensional CdS nanowires, nanobelts, and nanorods have shown great potential in electronic and optoelectronic applications. However, most nano-scale CdS Field Effect Transistors (FETs) work in the depletion-mode (D-mode) due to the high unintentional n-type doping concentration, which results in high power consumption under off-state. In addition, the large dark current limits to the specific detectivity when they are fabricated into phototransistors. Here, we have synthesized single crystal CdS nanobelts (NBs) on a SiO2/Si substrate via chemical vapor deposition. The CdS NB FETs were fabricated with HfO2 as a passivation layer. It is found that the working mode of the FETs was transformed from the D-mode to the enhancement-mode with the threshold voltage changing from −22.6 to 0.7 V due to the decrease in the defect density. The HfO2 passivated CdS NB phototransistor shows a responsivity of 4.7 × 104 A/W and an ultrahigh detectivity of 9.07 × 1014 Jones at the source-drain voltage of 1 V under an illumination wavelength of 450 nm. Our work demonstrates an effective way to achieve enhancement-mode CdS FETs and high performance phototransistors.

Halide-Induced Self-Limited Growth of Ultrathin Nonlayered Ge Flakes for High-Performance Phototransistors.

2D nonlayered materials have attracted intensive attention due to their unique surface structure and novel physical properties. However, it is still a great challenge to realize the 2D planar structures of nonlayered materials owing to the naturally intrinsic covalent bonds. Ge is one of them with cubic structure impeding its 2D anisotropic growth. Here, the ultrathin single-crystalline Ge flakes as thin as 8.5 nm were realized via halide-assisted self-limited CVD growth. The growth mechanism has been confirmed by experiments and theoretical calculations, which can be attributed to the preferential growth of the (111) plane with the lowest formation energy and the giant interface distortion effect of the Cl-Ge motif. Excitingly, a Ge flake-based phototransistor shows excellent performances such as a high hole mobility of ∼263 cm2 V-1 s-1, a high responsivity of ∼200 A/W, and fast response rates (τrise = 70 ms, τdecay = 6 ms), suggesting its great potential in the applications of electronics and optoelectronics.

High Performance Flexible Organic Phototransistors with Ultrashort Channel Length

Organic phototransistors with high responsivity and sensitivity to light irradiance have great potential applications in environmental monitoring, space exploration, security, image sensors and healthcare systems. In this manuscript, a novel polymer bulk heterojunction field effect phototransistor with ultrashort channel length (tens of nanometers) and ultrahigh sensitivity to visible light was proposed. Due to the nanoscale channel and bulk heterojunction structure, a high-performance phototransistor with high responsivity of 750 A/W, photosensitivity of 1.0 × 106, and detectivity as high as 4.54 × 1015 Jones was demonstrated under 720 nm light illumination with 0.1 mW/cm2 intensity, which was even better that those lateral organic phototransistors. Moreover, organic phototransistors with ultrashort channel length were investigated for the first time on a flexible substrate, which exhibited outstanding mechanical flexibility due to their unique designs. Further investigation of the correlation between th...

High-performance phototransistor based on individual high electron mobility MnWO4 nanoplate

MnWO4 nano-materials have been attracting intensive attention as a potential candidate for modern electronic and optoelectronic nanodevices. However, the availability of highly crystalline MnWO4 nanostructures with controllable geometry shapes still remains a great challenge and further hinders their technologically important applications in optoelectronic devices. Herein, large yield and crystalline MnWO4 nanoplates with regular crystal facets are synthesized on Ti substrate based on a conventional plasma electrolytic oxidation (PEO) process followed by a thermal annealing method. The phototransistor based on individual high electron mobility MnWO4 nanoplate has been fabricated and it shows a classical n-type semiconductor behavior with superior field emission transistor (FET) properties including a very low threshold voltage of 1 V and a high peak transconductance of 2.7 μS. Furthermore, the MnWO4 phototransistor also exhibits fast photoresponse time and high photoresponsivity under light illumination. All these unique characteristics of incident-light control and gate regulation from the MnWO4 nanoplate are expected to further promote its potential applications in multifunctional optoelectronic devices in the future.

Visible to near-infrared photodetectors based on MoS2 vertical Schottky junctions

Over the past few years, two-dimensional (2D) nanomaterials, such as MoS2, have been widely considered as the promising channel materials for next-generation high-performance phototransistors. However, their device performances still mostly suffer from slow photoresponse (e.g. with the time constant in the order of milliseconds) due to the relatively long channel length and the substantial surface defect induced carrier trapping, as well as the insufficient detectivity owing to the relatively large dark current. In this work, a simple multilayer MoS2 based photodetector employing vertical Schottky junctions of Au-MoS2-ITO is demonstrated. This unique device structure can significantly suppress the dark current down to 10−12 A and enable the fast photoresponse of 64 μs, together with the stable responsivity of ∼1 A W−1 and the high photocurrent to dark current ratio of ∼106 at room temperature. This vertical-Schottky photodetector can also exhibit a wide detection range from visible to 1000 nm. All these results demonstrate clearly that the vertical Schottky structure is an effective configuration for achieving high-performance optoelectronic devices based on 2D materials.

High-Performance Inorganic Perovskite Quantum Dot-Organic Semiconductor Hybrid Phototransistors.

All-inorganic lead halide perovskite quantum dots (IHP QDs) have great potentials in photodetectors. However, the photoresponsivity is limited by the low charge transport efficiency of the IHP QD layers. High-performance phototransistors based on IHP QDs hybridized with organic semiconductors (OSCs) are developed. The smooth surface of IHP QD layers ensures ordered packing of the OSC molecules above them. The OSCs significantly improve the transportation of the photoexcited charges, and the gate effect of the transistor structure significantly enhances the photoresponsivity while simultaneously maintaining high Iphoto /Idark ratio. The devices exhibit outstanding optoelectronic properties in terms of photoresponsivity (1.7 × 104 A W-1 ), detectivity (2.0 × 1014 Jones), external quantum efficiency (67000%), Iphoto /Idark ratio (8.1 × 104 ), and stability (100 d in air). The overall performances of our devices are superior to state-of-the-art IHP photodetectors. The strategy utilized here is general and can be easily applied to many other perovskite photodetectors.

Dual-Gate Phototransistor With Perovskite Quantum Dots-PMMA Photosensing Nanocomposite Insulator

Dual-gate InGaZnO thin-film-transistors were fabricated to demonstrate their feasibility as phototransistors by fully exploiting the perovskite quantum dots (QDs) with superior quantum yield. Here, we show that by coupling the top-gate photo sensing polymethyl methacrylate (PMMA)/CsPbBr3 QDs hybrid insulator with the classic SiO2 bottom-gate insulator, the phototransistor can exhibit a combination of excellent detective performance ( $3.75\times 10^{12}$ Jones detectivity and $1\times 10^{3}\text{A}$ /W responsivity) and electrical performance (small 3-V threshold voltage, 0.53-V/decade substhreshold slop, and 0.1-V hysteretic threshold voltage’s shift). Additionally, this dual-gate phototransistor exhibits high stability and accelerated detecting speed ( $ ) due to the inorganic perovskite QDs/PMMA hybrid gate insulator. Our results suggest that in a proper device architecture, perovskite nanomaterials can be promising candidates for cost-effective, high-performance phototransistor.

A new high-performance phototransistor design based on both surface texturization and graded gate doping engineering

In this paper, we propose a new optically controlled field effect transistor, OC-FET, based on both surface texturization and graded gate doping engineering. The proposed design consists of a gate with both graded doping and surface texturization aspects to ensure high efficient light absorption and low dark current, respectively. Moreover, using an analytical investigation, an overall performance comparison of the proposed dual texturized gate (DTG) OC-FET device and conventional OC-FETs has been studied in order to confirm the enhanced optical and electrical performance of the proposed design in terms of increased photoresponsivity (R), optical gain $$(G), I_{ON}/I_{OFF}$$(G),ION/IOFF ratio, drain current driving capability $$(I_{DMAX})$$(IDMAX) and high signal to noise ratio. Simulations show very good agreement between the results of the developed analytical models and those of TCAD software for wide range of design parameters. The developed analytical models are used to formulate the objective functions to optimize the device performance using a multi-objective genetic algorithm (MOGA). The proposed MOGA-based approach is used to search the optimal design parameters, for which the electrical and optical device performance is maximized. The obtained superior electrical performance suggests that our DTG OC-FET offers great promise as optical sensors and transducers for CMOS-based optical communications.

Synthesis and application of benzooxadiazole-based conjugated polymers in high performance phototransistors

Benzooxadiazole and benzothiadiazole based conjugated polymers have been synthesized and used for the fabrication of high performance phototransistors.

Role of metal contacts in high-performance phototransistors based on WSe2 monolayers.

Phototransistors based on monolayer transition metal dichalcogenides (TMD) have high photosensitivity due to their direct band gap transition. However, there is a lack of understanding of the effect of metal contacts on the performance of atomically thin TMD phototransistors. Here, we fabricate phototransistors based on large-area chemical vapor deposition (CVD) tungsten diselenide (WSe2) monolayers contacted with the metals of different work function values. We found that the low Schottky-contact WSe2 phototransistors exhibit a very high photo gain (10(5)) and specific detectivity (10(14)Jones), values higher than commercial Si- and InGaAs-based photodetectors; however, the response speed is longer than 5 s in ambient air. In contrast, the high Schottky-contact phototransistors display a fast response time shorter than 23 ms, but the photo gain and specific detectivity decrease by several orders of magnitude. Moreover, the fast response speed of the high Schottky-contact devices is maintained for a few months in ambient air. This study demonstrates that the contact plays an important role in TMD phototransistors, and barrier height tuning is critical for optimizing the photoresponse and photoresponsivity.