Thin-film Phototransistors Research Articles

Hydrogen chloride treated InAs quantum dot thin film phototransistor for ultrahigh responsivity

Indium Arsenide (InAs) colloidal quantum dots (CQDs) are emerging candidates for infrared photodetector applications owing to their excellent optoelectronic properties and low toxicity. However, low electron mobility stemming from its unique surface chemistry hinders its practical application. Through comprehensive structural and chemical analyses, we optimized the one-step HCl treatment to achieve stoichiometric balance, a well-passivated surface with low defect density, and an improved coupling effect by reducing the interparticle distance. Subsequently, a near infrared photodetector at a wavelength of 980 nm was fabricated with the modified InAs QDs in thin film transistor structure by all-solution process, showing remarkable electron mobility enhancement of up to 3.15 cm2/V∙s. The thin film phototransistor exhibited excellent photoresponse with a responsivity of 5.45 × 103 A/W, external quantum efficiency of 6.90 × 105%, and a linear dynamic range of 50 dB. This achievement represents the highest responsivity observed in an InAs QD-based phototransistor device, demonstrating its potential for lead-free infrared (IR) region optoelectronic applications.

Unraveling the Discrepancy on Persistent Photoconductivity Between Organic Single-Crystal and Thin-Film Phototransistors

Unraveling the Discrepancy on Persistent Photoconductivity Between Organic Single-Crystal and Thin-Film Phototransistors

Effect of SiO2 gate insulator on electrical performance of solution processed SnO2-Based thin film phototransistor

SnO2-based TFTs were fabricated by using the sol-gel spin coating method. SnO2 semiconductor films used as active layers were coated on oxidized Si with different SiO2 thicknesses. AFM was used to analyze the surface morphology. The oxidation states of SnO2 film for Sn3d and O1s were determined by XPS. The parameters demonstrating the electrical performance of a transistor such as mobility (μ), threshold voltage (Vth) and sub-threshold swing (SS) have been determined depending on the thickness of the dielectric layer. The thickness of the dielectric layer played an important role in the device's performance. The highest mobility and Ion/off values were obtained as 7.1 cm2/V.s and 6.98x104 for TFT fabricated with a 150 nm thick SiO2 layer. All the TFTs exhibited photosensing behavior at different light intensities and these results are an indicator that the SnO2 TFT can be effectively utilized in visible photo-detecting device applications.

InP Quantum Dots Tailored Oxide Thin Film Phototransistor for Bioinspired Visual Adaptation

AbstractThe exploration of bionic neuromorphic chips, capable of processing sensory data in a human‐like manner, is both a trend and a challenge. There is a strong demand for phototransistors that offer broadband in‐sensor adaptability. This study introduces a bioinspired vision sensor based on InP quantum dots (QDs)/InSnZnO hybrid phototransistors. This novel design combines the excellent electrical transportation features of oxide semiconductors with the superior optoelectronic response of InP QDs. The resulting hybrid devices exhibit exceptional gate controllability and a robust visible‐light response. These characteristics enable the emulation of multiple functions of the human visual system and the accommodation of varying light intensity environments. Furthermore, the phototransistor array successfully replicates the scotopic and photopic adaptation recognition behaviors of the human retina. Notably, the device demonstrates faultless competency in image processing, achieving an impressive 93% accuracy for digit recognition. These findings contribute to the advancement of bionic neuromorphic chips and offer promising opportunities for future developments in the bioinspired visual system.

47‐1: Ambipolar Gap‐type a‐Si‐TFT Circuit Applied for a Color Ambient Light Sensor

In this paper, we proposed ambient light sensor (ALS) and color temperature sensor (CTS) circuit integrated in the edge of LCD display panel. The designed circuit is based on the thin film transistor (TFT) technology, the photo TFT can produce high photo current under light for sensor realizing ambient light from 0~50000Lux. Also, CTS circuit are based on ALS circuit but covered with color filter. The result shows that CTS can discriminate different color temperature in ambient light. The biggest advantage of this sensor is that it is compatible with TFT process in manufacturing, and it is small in size and high in efficiency. It has the potential to replace photodiode sensors.

Heterojunction solar cell based on donor-acceptor pi-conjugated naphthalene bisbenzimidazole, perylene bisbenzimidazole, and naphthalene imidazole: A spectroscopic, microscopic and DFT assessment.

This study represents detailed vibrational analysis of naphthalene bisbenzimidazole (NBBI), perylene bisbenzimidazole (PBBI), and naphthalene imidazole (NI) by vibrational spectroscopic (Fourier Transform Infrared (FT-IR) and Raman), Atomic Force Microscopic (AFM) and quantum chemical studies for the first time. These sorts of compounds provide an opportunity to build potential n-type organic thin film phototransistors which can be used as organic semiconductors. Optimized molecular structures and vibrational wavenumbers of these molecules in their ground states have been calculated by Density Functional Theory (DFT) using B3LYP functional with 6-311++G(d,p) basis set. Finally, theoretical UV-Visible spectrum was predicted and Light Harvesting Efficiencies (LHE) were evaluated. AFM analysis revealed that PBBI has the highest surface roughness thus exhibits an increase in high Jsc value and high conversion efficiency.

High Performance Graphene-C60 -Bismuth Telluride-C60 -Graphene Nanometer Thin Film Phototransistor with Adjustable Positive and Negative Responses.

Graphene is a promising candidate for the next-generation infrared array image sensors at room temperature due to its high mobility, tunable energy band, wide band absorption, and compatibility with complementary metal oxide semiconductor process. However, it is difficult to simultaneously obtain ultrafast response time and ultrahigh responsivity, which limits the further improvement of graphene photoconductive devices. Here, a novel graphene/C60 /bismuth telluride/C60 /graphene vertical heterojunction phototransistor is proposed. The response spectral range covers 400-1800nm; the responsivity peak is 106 A W-1 ; and the peak detection rate and peak response speed reach 1014 Jones and 250 µs, respectively. In addition, the regulation of positive and negative photocurrents at a gate voltage is characterized and the ionization process in impurities of the designed phototransistor at a low temperature is analyzed. Tunable bidirectional response provides a new degree of freedom for phototransistors' signal resolution. The analysis of the dynamic change process of impurity energy level is conducted to improve the device's performance. From the perspective of manufacturing process, the ultrathin phototransistor (20-30nm) is compatible with functional metasurface to realize wavelength or polarization selection, making it possible to achieve large-scale production of integrated spectrometer or polarization imaging sensor by nanoimprinting process.

Efficient UV-Sensitive Si-In-ZnO-Based Photo-TFT and Its Behavior as an Optically Stimulated Artificial Synapse

Integration of optoelectronic synaptic devices as neuromorphic vision sensors has currently attracted significant attention due to their ability of imitating human visual systems. Low-power-consuming UV-sensitive phototransistors fabricated using amorphous oxide semiconductors are one of the potential contenders for the development of optically stimulated synaptic devices. Herein, amorphous Si-In-ZnO (a-SIZO)-based UV-sensitive photo thin-film transistors (photo-TFTs) were fabricated, which exhibited an efficient spectral photoresponsivity of 4.93 × 103 A/W and detectivity of 5.47 × 1015 jones at 350 nm wavelength. Considerable photoresponse in the visible range (450–650 nm) was also observed. The presence of persistent photoconductivity (PPC) in the photoresponse characteristics enabled the photo-TFT to perform simultaneously as an optically stimulated artificial synapse. The typical synaptic behaviors such as excitatory post-synaptic current (EPSC), pair-pulse facilitation (PPF), short-term plasticity (STP) to long-term plasticity (LTP), etc. were demonstrated efficiently by the fabricated photo-TFT, indicating its learning and memorizing capabilities similar to a biological synapse. The concurrent demonstration of efficient UV range photoresponse and optically stimulated synaptic behavior enables the a-SIZO-based photo-TFT as a promising pathway toward the development of artificial visual sensors which can be integrated into future neuromorphic systems.

Performance analysis of a new Mid-Infrared phototransistor based on combined graded band gap GeSn sensitive-film and IGZO TFT platform

In this paper, a novel InGaZnO (IGZO) thin-film Mid-Infrared phototransistor (TF MIR PT) based on GeSn capping layer with band-gap grading (BGG) aspect is proposed and numerically investigated. Accurate numerical models are developed to study the device characteristics, where the sensor optical properties under MIR light exposure are investigated using FDTD method. Importantly, a new systematic approach based on introducing a new Figure of Merit (FoM) parameter combining noise effects, power consumption and IR photoresponse characteristics is proposed to efficiently investigate the device performance. It is found that the use of IGZO TFT platform combined with BGG GeSn sensitive layer paves the way for achieving enhanced IR photodetection characteristics, while maintaining low dark-noise effects and reduced power consumption. Moreover, it is revealed that the use of GeSn capping layer with BGG paradigm enables extended spectral sensitivity to MIR ranges, showing a high cutoff wavelength of 2.4 μm. Besides, the proposed GeSn/IGZO TF MIR PT demonstrates a giant responsivity of 550 A/W at a specific wavelength value of 1.7 μm, detectivity of 2.5 × 1014 Jones and over than 168 dB of signal-to-noise ratio. Therefore, these findings open the perspective for the design of alternative MIR sensors, offering improved photoresponse, low noise and reduced power consumption, which are highly suitable for newly emerging CMOS-compatible optical communication and optoelectronic applications.

Development of all-solution processed CdSe thin film phototransistors with hybrid TiSiOx-PVP dielectric gate

We report a simple solution process to obtain hybrid TiSiOx-PVP dielectric films, at different molar concentrations, for dielectric gate applications in CdSe-based photo TFT. A set of hybrid films was deposited by spinning the precursor solutions with 1:1:1, 1:2:1, and 1:2:2 molar concentrations of PVP:SiO2:TiO2, respectively. These samples were analyzed by several experimental techniques. MIM and MIS capacitors were assembled to determine the hybrid films dielectric properties. The leakage current density was in the range of 10−8-10−5 A/cm2 at an electric field from 0 to 0.2 MV/cm, with a dielectric constant in the range from 4 to 8 at 1 MHz, depending on the composition. The hybrid layers were applied to the fabrication of solution-processed CdSe TFT on ITO-coated glass substrates. The all-solution processed TFT showed the capability for photodetection in a wide light wavelength range, operating at low voltage with very low hysteresis, mobility of 0.17 cm2/Vs, low threshold voltage of 1 V, low subthreshold swing of 0.17 V/dec, and on/off current ratio of 105.

Hybrid visible-blind ultraviolet photodetector based on NiO thin-film phototransistor and p-NiO/n-Si heterojunction diode

A hybrid visible-blind ultraviolet (UV) photodetector, which combines a p-NiO/n-Si heterojunction diode and NiO-based thin-film phototransistor, was proposed, and its optoelectronic properties were studied. The hybrid photodetector exhibited a high quantum efficiency and photocurrent gain. The p-NiO/n-Si heterojunction separates the photogenerated electron–hole pairs, thereby reducing the recombination probability of the electron–hole pairs and enhancing photocurrent gain. In the hybrid photodetector, the ratio of the photo current to dark current (IP/ID) increased with an increase in the drain source voltage (VDS) because more photogenerated holes were extracted. Responsivity decreased with increasing positive gate voltage (VG) owing to the depleted channel layer. Conversely, the responsivity increases with increasing negative VG because more holes are accumulated at the surface of the NiO channel layer. The UV (280 nm)/visible (500 nm) rejection ratio is as high as 700–850, indicating that the prepared hybrid device is a good visible-blind photodetector. Detectivity increased from 6.72 × 1012 to 2.23 × 1013 Jones by decreasing VG from 10 to −10 V. Band diagrams of p-NiO/n-Si heterojunction diodes and NiO-based thin-film phototransistors were proposed to elucidate the mechanism of the photocurrent gain in the prepared hybrid photodetector.

Bio-Inspired In-Sensor Compression and Computing Based on Phototransistors.

The biological nervous system possesses a powerful information processing capability, and only needs a partial signal stimulation to perceive the entire signal. Likewise, the hardware implementation of an information processing system with similar capabilities is of great significance, for reducing the dimensions of data from sensors and improving the processing efficiency. Here, it is reported that indium-gallium-zinc-oxide thin film phototransistors exhibit the optoelectronic switching and light-tunable synaptic characteristics for in-sensor compression and computing. Phototransistor arrays can compress the signal while sensing, to realize in-sensor compression. Additionally, a reservoir computing network can also be implemented via phototransistors for in-sensor computing. By integrating these two systems, a neuromorphic system for high-efficiency in-sensor compression and computing is demonstrated. The results reveal that even for cases where the signal is compressed by 50%, the recognition accuracy of reconstructed signal still reaches ≈96%. The work paves the way for efficient information processing of human-computer interactions and the Internet of Things.

Metaheuristic-based decision maker framework for the development of multispectral IGZO thin-film phototransistors

A new multispectral InGaZnO (IGZO) thin-film phototransistor (TF PT) based on a graded band-gap (GBG) SiGe capping layer with metallic nanoparticles (MNPs) is proposed. An accurate drain-current model is developed to investigate the device performances, where the optical characteristics under different light excitations (530 nm, 820 nm, and 1550 nm) are analyzed using the 3-D Finite-difference time-domain method (FDTD). It is found that the proposed device shows high photoresponse characteristics. Besides, it is revealed that the GBG configuration, MNPs spatial distribution and size can induce a complex behavior, which influences the device photoresponse over multiple spectral bands. Importantly, an iterative decision-maker framework based on the Multi-Objective Genetic Algorithm (MOGA) metaheuristic approach is implemented to design efficient multispectral IGZO TF PT. It is demonstrated that the proposed MOGA-based scheme paves the way for the designer to identify the appropriate GBG profile and MNPs spatial distribution for highly-responsive devices at selective Visible and IR wavelengths and to realize high-performance multispectral sensors. The proposed approach based on combining the proposed IGZO TF PT structure with MOGA metaheuristic computation opens up a new strategy for the design and experimental fabrication of high-performance multispectral optoelectronic devices.

DFT-FDTD modeling of a new broadband mid-infrared IGZO thin-film phototransistor based on black phosphorus capping layer incorporating intermediate metallic film

Here we present a new broadband mid-Infrared (mid-IR) InGaZnO (IGZO) thin-film phototransistor (TF PT) based on both Black Phosphorus (BP) capping layer incorporating gold (Au) intermediate ultrathin-film. The electronic and optical properties of bulk BP are carried out using density functional theory (DFT) computations, including Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA) and the screened hybrid (YS-PBE0) functionals with van der Waals correction. It is found that BP exhibits interesting performances for mid-IR optoelectronic applications, at room temperature. To enhance the absorption of the BP material for broadband mid-IR spectrum, a new strategy is proposed by optimizing the sensitive layer using finite-difference time-domain (FDTD) modeling and particle swarm optimization (PSO) approaches. The photoresponse properties of the optimized broadband mid-IR IGZO TF PT with BP/Au/BP capping layer are carefully analyzed. It is found that the proposed device shows high photodetection performances with a high current ratio exceeding 180 dB over a wide voltage window. Besides, it is revealed that the introduced ultrathin Au layer within BP enhances the absorbance capability over the mid-IR spectrum, which significantly improves the performance of the broadband mid-IR sensor. Therefore, the proposed approach based on combining DFT analysis with FDTD simulation supported by PSO optimization opens up a new strategy for the development of high-performance optoelectronic devices.

Tail state mediated conduction in zinc tin oxide thinfilm phototransistors under below bandgap optical excitation

We report on the appearance of a strong persistent photoconductivity (PPC) and conductor-like behaviour in zinc tin oxide (ZTO) thinfilm phototransistors. The active ZTO channel layer was prepared by remote plasma reactive sputtering and possesses an amorphous structure. Under sub-bandgap excitation of ZTO with UV light, the photocurrent reaches as high as ~ 10−4 A (a photo-to-dark current ratio of ~ 107) and remains close to this high value after switching off the light. During this time, the ZTO TFT exhibits strong PPC with long-lasting recovery time, which leads the appearance of the conductor-like behaviour in ZTO semiconductor. In the present case, the conductivity changes over six orders of magnitude, from ~ 10−7 to 0.92/Ω/cm. After UV exposure, the ZTO compound can potentially remain in the conducting state for up to a month. The underlying physics of the observed PPC effect is investigated by studying defects (deep states and tail states) by employing a discharge current analysis (DCA) technique. Findings from the DCA study reveal direct evidence for the involvement of sub-bandgap tail states of the ZTO in the strong PPC, while deep states contribute to mild PPC.

Efficiency enhancement of organic thin-film phototransistors due to photoassisted charge injection

Understanding the underlying physics of charge transport in organic semiconductors under illumination is important for the development of novel optoelectronic applications. We study the effects of monochromatic light in the visible spectrum on the channel of an organic thin-film transistor based on 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene. When the channel of the transistor was illuminated with red, green, or blue light, more charge carriers were measured than what exciton generation from photon absorption alone could provide, leading to a photon-to-charge-carrier conversion efficiency much larger than 100%. We explain this phenomenon using a model incorporating space-charge limited photocharges and enhanced hole injection from the source electrode due to lowering of the potential barrier by photogenerated electrons.

Enhanced infrared photoresponse of a new InGaZnO TFT based on Ge capping layer and high-k dielectric material

In this paper, a novel InGaZnO (IGZO) Infrared (IR) thin-film Phototransistor (Photo-TFT) consisting of Germanium capping layer (Ge-CL) and high-k dielectric material is proposed and numerically investigated. The role of introducing Ge-CL/IGZO heterojunction and high-k dielectric such as HfO 2 , ZrO 2 , Ta 2 O 5 and TiO 2 in achieving the dual benefit of IR photodetection ability and reduced dark noise effects is demonstrated. It is found that the proposed Ge-CL/IGZO Photo-TFT with appropriate gate oxide material can offer high detectivity of 2.3 × 10 14 Jones, superior current ratio exceeding 200 dB and high IR responsivity of 4.1 × 10 2 A/W. These enhancements are attributed to a mixture of two effects; firstly, the introduction of p-type Ge-CL leads to form a p-n junction with IGZO, thus enhancing the separation and transfer mechanisms of photo-induced electron/hole pairs. Secondly, the use of high-k dielectric materials enables better control of the channel conductivity , allowing reduced power consumption. Therefore, we believe that the use of Ge-CL with suitable high-k dielectric material pinpoints a new pathway to design high IR photoresponse sensors based on cost-effective IGZO TFT building block, which makes it potential alternative for high-performance optoelectronic systems. • A new high-performance IGZO-TFT-IR sensor is proposed. • The proposed sensor demonstrates high IR responsivity of 4.1 × 10 2 A/W. • A superb detectivity and an ultrahigh I ON /I OFF ratio are recorded. • The proposed sensor is a promising alternative for low power consumption photosensors.

Imaging Array and Complementary Photosensitive Inverter Based on P-Type SnO Thin-Film Phototransistors

P-type tin monoxide (SnO) thin-film phototransistors were developed with high photoresponsivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.94\times 10^{{5}}$ </tex-math></inline-formula> A/W and high detectivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.82\times 10^{{14}}$ </tex-math></inline-formula> Jones, and these values are, to the best of our knowledge, among the highest for the reported oxide-semiconductor-based phototransistors. The excellent performances of these phototransistors were further demonstrated by incorporating the devices into a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${10}\times {10}$ </tex-math></inline-formula> array to successfully image a letter “A” pattern. Furthermore, by integration of n-type indium gallium zinc oxide and p-type SnO thin-film phototransistors, we realized a complementary photosensitive inverter. The inverter exhibits excellent photoresponse with a high voltage gain rate change of 194%. Our results indicates that the SnO based phototransistors have great potential in thin-film photoelectronic circuits and systems.

Organic single crystal phototransistors: Recent approaches and achievements

Organic phototransistors (OPTs), compared to traditional inorganic counterparts, have attracted a great deal of interest because of their inherent flexibility, light-weight, easy and low-cost fabrication, and are considered as potential candidates for next-generation wearable electronics. Currently, significant advances have been made in OPTs with the development of new organic semiconductors and optimization of device fabrication protocols. Among various types of OPTs, small molecule organic single crystal phototransistors (OSCPTs) standout because of their exciting features, such as long exciton diffusion length and high charge carrier mobility relative to organic thinfilm phototransistors. In this review, a brief introduction to device architectures, working mechanisms and figure of merits for OPTs is presented. We then overview recent approaches employed and achievements made for the development of OSCPTs. Finally, we spotlight potential future directions to tackle the existing challenges in this field and accelerate the advancement of OSCPTs towards practical applications.

The Characteristics of Aluminum-Gallium-Zinc-Oxide Ultraviolet Phototransistors by Co-Sputtering Method

In this thesis, Aluminum-Gallium-Zinc oxide (AGZO) photo thin film transistors (PTFTs) fabricated by the co-sputtered method are investigated. The transmittance and absorption show that AGZO is highly transparent across the visible light region, and the bandgap of AGZO can be tuned by varying the co-sputtering power. The AGZO TFT demonstrates high performance with a threshold voltage (VT) of 0.96 V, on/off current ratio of 1.01 × 107, and subthreshold swing (SS) of 0.33 V/dec. Besides, AGZO has potential for solar-blind applications because of its wide bandgap. The AGZO PTFT of this research can achieve a rejection ratio of 4.31 × 104 with proper sputtering power and a rising and falling time of 35.5 s and 51.5 s.