Performance Of Phototransistors Research Articles

2D layered halide perovskite for field-effect transistors

Field-effect transistors are crucial components for modern electronics, generating significant research and profitable interest. Metal halide perovskites have recently emerged as a pioneering active material in solar cells, generating interest in their potential use in other electronic and (opto)electronic devices, including field-effect transistors and phototransistors. However, before they can be commercialized, they still face significant challenges owing to their immanent instabilities with respect to heat, moisture, and light. In contrast, due to their exceptional environmental stability, the newly emerging two-dimensional Ruddlesden–Popper type perovskites have garnered significant recognition. The current state of the field is covered in this review article, as are the problems, and a perspective for the scenarios of perovskite field-effect transistors. The effects of temperature, light, and measurement conditions are taken into account, as well as the physics of the device and the fundamental mechanisms that drive these devices, such as ion migration and ionic defects. Subsequently, the performance of perovskite transistors and phototransistors described so far is analyzed and critically evaluated. Finally, the major roadblocks to perovskite transistor advancement are identified and explored. The lessons learned from other perovskite optoelectronic devices are investigated in order to address these obstacles and bring these devices closer to industrial implementation.

Ultrahigh-performance heterojunction bipolar phototransistor enabled by bilateral piezoelectric charge modulation effect

Heterojunction photodiodes based on p-n junction with enhanced piezo-phototronic effect have been extensively studied. However, the photoresponsivity of conventional photodiodes is small due to the natural zero current gain. Heterojunction phototransistor usually has greater photoresponsivity due to the non-zero current gain. More importantly, heterojunction phototransistor owns two interfaces, offering the opportunity to introduce the bilateral piezoelectric charge modulation effect for further performance enhancement compared to the conventional single-interface piezo-phototronic effect in photodiode. In this work, a base-floating heterojunction bipolar phototransistor (FHPT) based on n-ZnO/p-Si/n-ZnO structure with a spectral detection range from ultraviolet (UV)–visible is demonstrated. The positive piezoelectric charge generated at the two interfaces of the collector junction and the emitter junction, combined with the optimal base width and low resistance base doping concentration of the FHPT, leads to an excellent photoresponsivity (18046 A/W, 365 nm), high detectivity (5.7×1012 Jones), and a wider modulation (7120 %). The physical mechanism leading to the ultrahigh performance is attributed to the cooperative positive piezoelectric charge at the two interfaces, simultaneously reducing the effective base width and lowering the emitter junction barrier. This work illustrates the regulation of heterojunction phototransistor performance by the bilateral piezoelectric charge modulation effect, providing insightful guidance to high-performance phototransistor design.

Ultrathin Niobium‐Doped Indium Oxide Active Layer Enables High‐Performance Phototransistors for Driving Quantum‐Dot Light‐Emitting Diodes

AbstractActive materials play a crucial role in the performance of phototransistors. However, the discovery of a novel and versatile active material is a big challenge. For the first time, phototransistors with ultrathin niobium‐doped indium oxide (InNbO) active layer are fabricated. The InNbO phototransistors without additional light‐absorbing layers exhibit the performance with a high average mobility of 22.86 cm2 V−1s−1, a turn‐on voltage of −0.75 V, a low sub threshold swing of 0.18 V/decade, and a high on/off current ratio of 5.74 × 108. Detailed studies show that Nb is the key to suppress the free carrier generation due to the strong bonding strength of Nb─O. In addition, the InNbO phototransistors exhibit a very broad spectral responsivity with a photocurrent of 4.72 × 10−4 A, a photosensitivity of 1.69 × 108, and a high detectivity of 3.33 × 1013 Jones under violet (405 nm) light illumination, which is significantly higher than that of the IGZO phototransistors. Furthermore, an active‐matrix quantum‐dot light‐emitting diode pixel circuit based on InNbO phototransistors is demonstrated. The findings not only indicate that InNbO is a new active material for phototransistors, but also suggest that InNbO‐based phototransistors have a great potential for the next‐generation interactive display technology.

Enhancing the performance of organic phototransistors using a sandwich-heterostructure.

To weaken the adverse effects of traditional planar heterojunctions on phototransistors, an effective strategy for achieving low dark-current and high photoresponsive organic phototransistors via constructing a sandwich heterostructure is demonstrated. This work offers a new route for the design and development of high-performance phototransistor devices.

Enhanced performance of MoS2 phototransistors with ferroelectric HfLaON as gate dielectric through NH3-plasma treatment followed by rapid thermal annealing

A novel processing method of NH3-plasma treatment followed by rapid thermal annealing (RTA) is used to prepare HfLaON ferroelectric thin films, and obviously enhanced remanent polarization (Pr) and largely decreased gate leakage are obtained. The relevant HfLaON MoS2 phototransistor exhibits a subthreshold swing of 31 mV/dec and remarkable responsivity/detectivity of 941.37 AW−1/3.326 × 1014 cmHz1/2 W−1 at low operating voltages (gate-source voltage of −0.3 V and drain-source voltage of 0.4 V). Meanwhile, the response time of (NH3 plasma + RTA) phototransistor is significantly reduced to 8–12 ms compared to 33∼31 ms for the RTA phototransistor. Microscopic analyses indicate that the involved mechanisms lie in an effective incorporation of N element into the HfLaON thin film to passivate oxygen vacancies and improve interfacial properties. This work provides an effective way to rectify interface issues and optimize the ferroelectric properties of HfLaON thin films, demonstrating a good application prospects of HfO2-based ferroelectric thin films in 2D material-based photodetection field.

Enhancement‐Mode Phototransistors Based on β‐Ga2O3 Microflakes Fabricated by Focused Ion Beams

AbstractThis study introduces focused ion beam (FIB) processing for the first time to etch and thin β‐Ga2O3 microflakes, while exploring the effect of their thicknesses on the phototransistor performance. It is found that when the β‐Ga2O3 microflakes reach a certain thickness, the phototransistors switch from the depletion mode to the enhancement mode, exhibiting extremely low dark current without a gate voltage. The enhancement‐mode phototransistor prepared using this method demonstrates a photo‐dark current ratio as high as 2.3 × 105, a responsivity of 6.3 × 104 A W−1, and an external quantum efficiency of 3.1 × 107% when irradiated with incident light at a wavelength of 254 nm and a power density of 8 µW cm−2. Additionally, the device has a rise time of 43 ms and a fall time of 28 ms, respectively. By using FIB processing to etch and thin β‐Ga2O3 microflakes, this study effectively overcomes the poor controllability and low repeatability associated with the traditional mechanical exfoliation method, as well as the residual impurities from the plasma etching method. This opens up a new avenue for fabricating the high‐performance, low‐dimensional phototransistors based on β‐Ga2O3 with high repeatability and controllability.

Tunable Light Response Modulated by the Organic Interface Charge Transfer Effect

AbstractThe combination of a donor (D) and an acceptor (A) is viewed as a promising approach to achieve high performance phototransistors, owing to their advantages in exciton dissociation and charge trapping. The electronic properties at the D‐A interface can vary substantially with the choice of materials, and how to precisely control the interface properties to achieve a controllable light response behavior is still an open question. Herein, a series of D‐A heterostructure is reported with varying electronic structures of the acceptor and demonstrate the ability to tune the performance and photocurrent decay behaviors. Two distinct types of charge transfer phenomena, ground state, and excited state charge transfer, are identified originating from the specific different energy level alignment and lead to the improved photoresponsivity up to 104 AW−1 and the significantly varied photosensitivity ranging from 102 to approaching 107. Furthermore, the distinct charge transfer scenarios elicit diverse temporal responses, encompassing both short‐term synaptic behavior as well as persistent memory characteristics. These findings shed light on the importance of understanding and controlling charge transfer property for phototransistor performance and applications. The ability to modulate the temporal responses opens up new possibilities for designing devices with desired memory and synaptic functionalities.

Correlative Spatial Mapping of Optoelectronic Properties in Large Area 2D MoS2 Phototransistors

Abstract2D materials‐based device performance is significantly affected by film non‐uniformity, especially for large area devices. Here, it investigates the dependence of large area 2D MoS2 phototransistor performance on film morphology through correlative mapping. Monolayer MoS2 films are quazi‐epitaxially synthesized on C‐plane sapphire (Al2O3 ) substrates by chemical vapor deposition, and the growth time and molybdenum trioxide MoO3 precursor volume are varied to obtain variations in film morphology. Raman, photoluminescence, transmittance, and photocurrent maps are generated and compared with each other to obtain a holistic understanding of large area 2D optoelectronic device performance. For example, it shows that the photoluminescence peak shift and intensity can be used to investigate strain and other defects across multiple film morphologies, giving insight into their effects on the photogenerated current in these devices. It also combines photocurrent and absorption maps to generate large area high‐resolution external quantum efficiency and internal quantum efficiency maps for the devices. This study demonstrates the benefit of correlative mapping in the understanding and advancement of large area 2D material‐based electronic and optoelectronic devices.

Improving phototransistor performance with polymer-quantum dot hybrid technology

Herein, the infrared photodetection performance of the HgTe quantum dots embedded in a polymer matrix was studied using an FDTD solution. The role of P3HT polymer in the hybrid structure was investigated by focusing on optical enhancements. The simulation explored critical parameters such as photo absorption capabilities, electric field distribution, and electrical generation rate. Also, the effect of phase separation level on device performance was studied by changing the quantum dot cluster size. A phototransistor was fabricated using the hybrid structure with silver electrodes to examine the theoretical works. Incorporating P3HT polymer into the active medium of the device showed significant improvement in current density value at room temperature.

Enhancing the Performance of Organic Phototransistors Based on Oriented Floating Films of P3HT Assisted by Al-Island Deposition.

The fabrication of high-performance Organic Phototransistors (OPTs) by depositing Al-islands atop Poly(3-hexylthiophene) (P3HT) thin film coated using the unidirectional floating-film transfer method (UFTM) has been realized. Further, the effect of Al-island thickness on the OPTs' performance has been intensively investigated using X-ray photoelectron spectroscopy, X-ray Diffraction, Atomic force microscopy and UV-Vis spectroscopy analysis. Under the optimized conditions, OPTs' mobility and on-off ratio were found to be 2 × 10-2 cm2 V-1 s-1 and 3 × 104, respectively. Further, the device exhibited high photosensitivity of 105, responsivity of 339 A/W, detectivity of 3 × 1014 Jones, and external quantum efficiency of 7.8 × 103% when illuminated with a 525 nm LED laser (0.3 mW/cm2).

Electronic Modulation of Semimetallic Electrode for 2D van der Waals Devices

The 2D semimetallic electrodes have been employed to show outstanding contact properties with 2D semiconducting transition‐metal dichalcogenides (TMDCs) channel, leading to large enhancement of 2D transistor and phototransistor performance. Herein, an innovative concept is established for a unique 2D semimetallic electrode‐2D TMDC channel (2D–2D) device configuration where the electronic structures of 2D semimetallic electrodes are systematically modulated to improve the contact properties with 2D monolayer molybdenum disulfide (MoS2) channel. The 2D semimetallic copper sulfide (CuS) electrodes are doped with iodine atoms by a direct exposure of iodine gas. The contact properties and charge‐transport behavior in the 2D–2D field‐effect transistors (FETs) are highly improved, which is attributed to the favorable energy band alignment and associated material properties between the iodine‐doped CuS (CuS–I) electrodes and 2D channel. The 2D–2D FETs show a high on current, high on/off ratio, and twofold improvement in mobility. Furthermore, 2D–2D phototransistors and flexible/transparent photodetectors are fabricated using the CuS–I/MoS2, which also performed outstanding photoresponsivity characteristics and mechanical durability under external bending strain conditions. These findings demonstrate a promising pathway that under the 2D–2D configuration, the electronic modulation by the iodine atoms may enable the development of future 2D electronic applications.

Effects of Asymmetric Source-Drain Electrodes and Their Modifications on the Operation of Organic Phototransistors

Asymmetric source and drain (S-D) electrodes and their interfacial modifications have significant effects on the charge injection and transport in organic field-effect transistors, however their effects on the operation and performance of organic phototransistors (OPTs) are unknown. Herein, OPTs with symmetric (Ag-Ag, Au-Au) and asymmetric (Au-Ag, Au-bathocuproine (BCP)/Ag, Au/MoO3-BCP/Ag) S-D electrodes were fabricated and their performances were investigated. The results demonstrated that the devices with asymmetric S-D electrodes are superior than their counterparts with symmetric S-D electrodes. Among the three devices with asymmetric S-D electrodes Au-BCP/Ag device exhibits the highest photo responsivity of 36.6 A/W and external quantum efficiency of 7000%, meanwhile Au-BCP/Ag and Au/MoO3-BCP/Ag device exhibit significantly larger specific detectivity than Au-Ag device. The result gives an important guideline for designing high performance OPTs.

Boosting Phototransistor Performance in Monolayer TMDs via Multiple Reflections from DBR.

Transition-metal dichalcogenides (TMDs) are intensively studied for high-performance phototransistors. However, the device performance is limited by the single photoexcitation. Here, we show a unique strategy in which phototransistor performance can be boosted by fabricating the device on top of a distributed Bragg reflector (DBR). Monolayer molybdenum disulfide (MoS2) and tungsten disulfide (WS2) phototransistors were fabricated on DBR and SiO2 substrates for comparison. Furthermore, phototransistor performances including photocurrent, responsivity, photoinduced mobility, and subthreshold swing highlight 582 times enhancement in photoresponsivity ratio and 350 times enhancement in photocurrent ratio in the DBR sample using transparent graphene electrode and hBN encapsulation.

Comprehensive analysis of optoelectronic performance of ultraviolet phototransistors based on AlGaN/GaN heterostructure

Optoelectronic performance of ultraviolet phototransistors (UVPTs) based on AlGaN/GaN high-electron-mobility transistor (HEMT) configuration is comprehensively studied under different illumination wavelengths, light power densities, gate biases, and drain voltages. A special photoresponse mechanism combining photovoltaic effect and photoconductive effect is proposed to explain the variation of detection performance with the optical and electrical conditions. By comparing the photoreponse characteristics under typical illumination wavelengths of 310 and 360 nm, the optoelectronic properties of the HEMT-based UVPTs are deeply revealed and summarized. This work can provide suggestions and guidelines for designing of AlGaN/GaN-based UVPTs in III–V integrated photonic systems.

Performance enhancement of multilayer MoS2 phototransistors via photoresist encapsulation

We propose the encapsulation of bottom-gate multilayer MoS2 phototransistors with an AZ®5214E photoresist as an effective device design to enhance the optoelectronic properties of the phototransistors. The photoresist-encapsulated MoS2 phototransistors, based on mechanically exfoliated MoS2 crystals, exhibited an improved device performance. After the photoresist encapsulation, the responsivity and detectivity of the device increased by seven-fold to 3.2 × 103 A W−1 and by five-fold to 2.3 × 1012 Jones, respectively, under a 650-nm laser with an incident power density of 2.1 mW cm−2. We attribute the observed enhancement in the phototransistor performance to the enhanced electrical properties owing to the n-type doping via photoresist encapsulation. These results demonstrate that MoS2 phototransistors can achieve high performance without complicated device architecture and process, and thus, photoresist encapsulation presents an effective method for developing high-performance two-dimensional optoelectronic devices.

Analysis of the Effect of Adding PNP Phototransistors on Fiber Optic Systems

This study analyzes the performance of PNP phototransistors made of Gallium Arsenide (GaAs) and Silicon (Si). Based on the analysis for gallium arsenide and silicon PNP phototransistors, the emitter current at the output is greater than the photon current at the incident. With?= 1017?3;?= 1016?3and?= 1019?3;?= 1016?3The input current for GaAs material is 1.6865×10?7 ., respectively?and 8.0331×10?6A. With the addition of internal gain on the GaAs material, namely; common-base internal gain (?)= 0.9991; 0.8974 and the common-emitter internal gain(?)=1125; 8.7488, then each output current is 1.8973×10?4?and 7.028×10?5?. With the addition of the internal gain on the phototransistor, we get SNR = 26256 and 8022.As for the silicone material with?= 1017m3;?= 1016?3and?= 1019?3;?= 1016?3the input current and output current are respectively 1.0766×10?7?and 1,266×10?6?. With the internal gain on the silicon material, namely; for common-base internal gain(?)=0.9994; 0.9220 and the common-emitter internal gain(?)= 1563; 11,818, then the output currents are 1.6831×10?4A and 1.4827×10?5A, respectively. With the addition of the internal gain, the SNR for silicon is 8.3766×10?5 and 3.3609×10?6, respectively.

Fluorinated Dielectrics‐Modulated Organic Phototransistors and Flexible Image Sensors

AbstractIt is generally believed that the incorporation of fluorine functional groups into dielectrics can effectively impede the charge‐trapping process and improve carrier mobility. However, the relationship between the device performance and fluorinated groups is still not clear and also the modulation effect of fluorine functional groups on photogenerated charge carrier in phototransistors has not yet been investigated. Herein, phototransistors are constructed by using three kinds of gate dielectric layers with different fluorinated groups to exploit the effect of fluorine functional groups. It is concluded that the presence of fluorinated groups indeed increases the transistor mobility and optical figures of merit in phototransistors compared to the device with a fluorine‐free dielectric layer. Concurrently, the exciton binding energy is increased with the addition of fluorinated groups, resulting in the decrease of phototransistor performance compared with less content of fluorinated groups due to the synergistic balance effect of fluorine functional groups. The results further clarify how the fluorine functional groups optimize the interface of organic phototransistors and modulate the photoelectric performance.

Diffusion interface layer controlling the acceptor phase of bilayer near-infrared polymer phototransistors with ultrahigh photosensitivity

The narrow bandgap of near-infrared (NIR) polymers is a major barrier to improving the performance of NIR phototransistors. The existing technique for overcoming this barrier is to construct a bilayer device (channel layer/bulk heterojunction (BHJ) layer). However, acceptor phases of the BHJ dissolve into the channel layer and are randomly distributed by the spin-coating method, resulting in turn-on voltages (Vo) and off-state dark currents remaining at a high level. In this work, a diffusion interface layer is formed between the channel layer and BHJ layer after treating the film transfer method (FTM)-based NIR phototransistors with solvent vapor annealing (SVA). The newly formed diffusion interface layer makes it possible to control the acceptor phase distribution. The performance of the FTM-based device improves after SVA. Vo decreases from 26 V to zero, and the dark currents decrease by one order of magnitude. The photosensitivity (Iph/Idark) increases from 22 to 1.7 × 107.

Impact of base bias current and incident optical power on the InP/InGaAs heterojunction phototransistor performances

In this article, the optical and electrical properties of NPN InP/InGaAs heterojunction bipolar phototransistor (HPT) are studied by two dimensional semiconductor simulation. The phototransistor is modelled using a numerical method, and the results are presented and discussed. This model is based on heterojunction bipolar transistor (HBT) model with the consideration of the optical beam effect. Responsivity of 12.62 A/W for 1100 nm light is achieved when the thickness of base layer is 50 nm. A good qualitative agreement of the numerical and analytical simulated value of both collector current and responsivity as a function of the wavelength with the existing experimental data was achieved. We present a comparative analysis of our obtained solutions at IB = 5 μA with that simulated at IB = 100 μA and we found that the value of optical power (Popt) giving high injection into a phototransistor at IB = 5 μA is three times higher than that at IB = 100 μA. The effects of both the base bias current and the incident optical power on the device performance are investigated. The simulation results, which are presented and compared at low, ideal and high base bias current, show that the highest photocurrent and optical gain are obtained when the base bias current reaches the ideal region. The HPT optical characteristics such as the electrical characteristics of HBT are affected by the high injection effect (Kirk effect).

Electrode‐Induced Self‐Healed Monolayer MoS2 for High Performance Transistors and Phototransistors (Adv. Mater. 41/2021)

Self-Healing Devices An innovative concept of a self-healed electrode-channel system employing ultrathin metallic copper monosulfide (CuS) and monolayered molybdenum disulfide (MoS2) is demonstrated by John Hong, SeungNam Cha, and co-workers in article number 2102091 for the design of defect-curable transistors and phototransistors. Excess sulfur adatoms from the CuS electrode spontaneously heal the defect sites in the MoS2 channel for record-high transistor and phototransistor performance.