Field-effect Phototransistors Research Articles

Electronic transport characteristics and nanodevice designs for β-HfNCl monolayer

The mechanical properties, electronic structure, electric transport and optoelectronic properties of a recently predicted wide bandgap semiconductor β-HfNCl monolayer are systematically studied by means of first-principles calculations. β-HfNCl monolayer is isotropic in mechanical properties, whose calculated Young’s modulus, shear modulus, and layer modulus of β-HfNCl monolayer are 128.9–129.2, 44.28, and 119.46 N m−1, respectively. An appropriate tensile strain (i.e., beyond 3 %) can induce a transition from indirect bandgap to direct bandgap. In addition, we construct several conceptual nanodevice structures based on β-HfNCl monolayer, such as pn-junction diodes, pin-junction field-effect transistors (FETs) and phototransistors. The electronic transport results reveal that the pn-junction diodes have obvious rectification effect and strong electric anisotropy. Their rectification ratios and electric anisotropy ratio (η) can reach up to 106 and 3.69, respectively. The FETs have an obvious field-effect behavior with a slightly lower rectification ratio (105). Moreover, we investigate the photoelectric response of the phototransistors of β-HfNCl monolayer under the illumination of light. They have a strong response to the light whose energy is larger than the violet light, indicating that the β-HfNCl monolayer can be a platform to detect the ultraviolet light. These findings provide crucial insights into the potential applications of β-HfNCl monolayer in electronic and optoelectronic devices.

Anthracene-[1]benzothieno[3,2-b][1]benzothiophene (BTBT) dyad and triads as p-type semiconductors for organic field-effect transistors and phototransistors

[1]Benzothieno[3,2-b][1]benzothiophene (BTBT) and anthracene (An) are the most promising planar building blocks for constructing p-type small molecules for high-performance organic field-effect transistors (OFETs).

Van der Waals 2D transition metal dichalcogenide/organic hybridized heterostructures: recent breakthroughs and emerging prospects of the device.

The near-atomic thickness and organic molecular systems, including organic semiconductors and polymer-enabled hybrid heterostructures, of two-dimensional transition metal dichalcogenides (2D-TMDs) can modulate their optoelectronic and transport properties outstandingly. In this review, the current understanding and mechanism of the most recent and significant breakthrough of novel interlayer exciton emission and its modulation by harnessing the band energy alignment between TMDs and organic semiconductors in a TMD/organic (TMDO) hybrid heterostructure are demonstrated. The review encompasses up-to-date device demonstrations, including field-effect transistors, detectors, phototransistors, and photo-switchable superlattices. An exploration of distinct traits in 2D-TMDs and organic semiconductors delves into the applications of TMDO hybrid heterostructures. This review provides insights into the synthesis of 2D-TMDs and organic layers, covering fabrication techniques and challenges. Band bending and charge transfer via band energy alignment are explored from both structural and molecular orbital perspectives. The progress in emission modulation, including charge transfer, energy transfer, doping, defect healing, and phase engineering, is presented. The recent advancements in 2D-TMDO-based optoelectronic synaptic devices, including various 2D-TMDs and organic materials for neuromorphic applications are discussed. The section assesses their compatibility for synaptic devices, revisits the operating principles, and highlights the recent device demonstrations. Existing challenges and potential solutions are discussed. Finally, the review concludes by outlining the current challenges that span from synthesis intricacies to device applications, and by offering an outlook on the evolving field of emerging TMDO heterostructures.

Influence of the Bound Electron-Hole Pairs Dissociation Probability Field Dependence Form on the Photocurrent and Spatial Resolution of Organic Field Phototransistors

In this work, numerical simulations are used to study ambipolar organic field-effect phototransistors, in which a spatially localized photoelectric effect can take place. This effect consists in the fact that there is a small spatially localized photosensitive region in the transistor channel, the position of which can be controlled by changing the gate voltage. The purpose of this work is to analyze the relationship between the form of the field dependence of the bound electron-hole pairs (𝑒/ℎ pairs) dissociation probability and characteristics of the studied ambipolar phototransistors such as normalized photocurrent, spatial resolution, and response time. It is shown that the optimal form of the field dependence of 𝑒/ℎ pairs dissociation probability is stepwise-like form, which can provide a high spatial resolution at high values of the normalized photocurrent without degrading the response time of the phototransistor. This shape can be achieved when the organic semiconductor has an extremely narrow distribution of 𝑒/ℎ pairs by size, described by the delta function. Also, on the example of several distributions of various shapes, it is shown that a decrease in the width of the distribution leads to an increase in the spatial resolution. Approaches to the selection and modification of organic semiconductor materials that would provide the most pronounced spatially localized photoelectric effect in ambipolar field-effect transistors are discussed.

Influence of the Bound Electron–Hole Pairs Dissociation Probability Field Dependence Form on the Photocurrent and Spatial Resolution of Organic Field-Effect Phototransistors

Influence of the Bound Electron–Hole Pairs Dissociation Probability Field Dependence Form on the Photocurrent and Spatial Resolution of Organic Field-Effect Phototransistors

Ferroelectric La-doped HfO2 deposited via chemical solution on silicon for tellurium field-effect phototransistors

Chemical solution deposition (CSD) is proven viable, low-cost technique for growing thin films of various functional materials. This technique is also employed in the growth of doped-HfO2, aimed at comprehending the effectiveness of dopants in inducing ferroelectricity in HfO2; various dopants such as Zr, Y, Al, Ce, Ba have been investigated over the years. Herein, we now aim to extend the efficacy of CSD in achieving high ferroelectric output in La-doped HfO2 (HLO) directly on silicon. CSD-HLOs exhibit a remarkable remanent polarization (2Pr) of ≈ 37 µC/cm2 and coercive field (Ec) of ∼ 3 MV/cm. These CSD-HLOs when stacked with HfO2 dielectric and tellurium (Te) p-type semiconducting channel, the resulting field effect transistors (FETs) have not only demonstrated four-fold improvement in the switching characteristics but also substitutionally reduced the leakage currents. The FETs on passivation with Al2O3 demonstrated excellent stability against applied stress and these passivated FETs presented good optical response under blue light through the photogating.

Novel Group-IV Alloy-Based MOS Field-Effect Phototransistors for Near-Infrared Applications

This work describes the novel Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> alloy-based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -metal-oxide-semiconductor phototransistors (nMOSPTs) grown on silicon (Si) substrate via Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> =3.6%) virtual substrate (VS) for near-infrared (NIR) applications. The concept of transferring high-speed optical signals directly to the complementary metal-oxide-semiconductor (CMOS) photodetector paves the way for novel applications of light to aid electrical functions. As a channel material, SiSn is used in the proposed device’s structure. For the purpose of fabricating CMOS devices, the key benefit of using SiSn as a channel material is that it is inexpensive and compatible with Si substrates. In this study, SiSn with 3.6% Sn is introduced as a VS to minimize the lattice mismatch between the Si substrate and Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> =5%- 24% active layer. The bandgap shrinks as Sn is incorporated into Si, which results in a wavelength redshift. As a result, the photodetection range shifts toward a longer wavelength. Moreover, the Sn alloying results in a high absorption coefficient, which increases the responsivity of the device. The designed device is simulated using a commercially available multiphysics tool. The proposed device with a 1000 nm channel length, shows the responsivity and bandwidth of 15.8 A/W and 4.8 GHz, respectively at λ = 850 nm with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_GS</i> = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_DS</i> = 1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> =5%. By increasing the Sn concentration to 24% and gate and drain voltages to 4V, the proposed device achieves the responsivity and bandwidth of 2260 A/W and 61.7 GHz, respectively. Furthermore, it is expected that miniaturization would enhance future devices’ responsivity and bandwidth.

High performance InGaN/GaN visible-light field effect phototransistor using polarization induced virtual photogate

Visible-light field effect phototransistors (FEPTs) with high detectivity and high speed are fabricated using a polarization induced photogate in a simple In0.15Ga0.85N/GaN heterostructure, where the pure polarization electric field acts as a virtual photogate of the FEPT and the total In0.15Ga0.85N layer plays the roles of absorber and channel. Experimental results show that the polarization electric field from high quality pseudo-crystalline InGaN/GaN structure can fully deplete the channel layer and leads to an ultra-low dark current. Furthermore, the channel conductivity can be significantly promoted with visible-light illumination. Therefore, the FEPT achieves a high visible-light gain of 6.0 × 104 and a superhigh shot noise limited specific detectivity of 1.5 × 1016 Jones, as well as a high speed with 15 ns/160 ns rise/fall time. The results not only present huge potential in visible-light photodetection, but also provide an insight into the application of polarization effects in wide bandgap semiconductors.

Simulating the obstacle avoidance behavior day and night based on the visible-infrared MoS2/Ge heterojunction field-effect phototransistor

Simulating the obstacle avoidance behavior day and night based on the visible-infrared MoS2/Ge heterojunction field-effect phototransistor

AlGaN solar-blind phototransistor capable of directly detecting sub-fW signals: self-depletion and photorecovery of full-channel 2DEG enabled by a quasi-pseudomorphic structure

Heterojunction field-effect phototransistors using two-dimensional electron gas (2DEG) for carrier transport have great potential in photodetection owing to its large internal gain. A vital factor in this device architecture is the depletion and recovery of the 2DEG under darkness and illumination. This is usually achieved by adding an external gate, which not only increases the complexity of the fabrication and the electrical connection but also has difficulty ensuring low dark current (I dark ). Herein, a quasi-pseudomorphic AlGaN heterostructure is proposed to realize the self-depletion and photorecovery of the 2DEG, in which both the barrier and the channel layers are compressively strained, making the piezoelectric and spontaneous polarization reverse, thus depleting the 2DEG and tilting the entire barrier and channel band to form two built-in photogates. The fabricated solar-blind phototransistors exhibit a very low I dark below 7.1×10−10 mA/mm, a superhigh responsivity (R) of 2.9×109 A/W, a record high detectivity (D*) of 4.5×1021 Jones, and an ultrafast response speed at the nanosecond level. The high performance is attributed to the efficient depletion and recovery of the full 2DEG channel by the two photogates, enabling direct detection of the sub-fW signal. This work provides a simple, effective, and easily integrated architecture for carrier control and supersensitive photodetection based on polarization semiconductors.

Polarity-Tunable Field Effect Phototransistors.

Field-effect phototransistors feature gate voltage modulation, allowing dynamic performance control and significant signal amplification. A field-effect phototransistor can be designed to be inherently either unipolar or ambipolar in its response. However, conventionally, once a field-effect phototransistor has been fabricated, its polarity cannot be changed. Herein, a polarity-tunable field-effect phototransistor based on a graphene/ultrathin Al2O3/Si structure is demonstrated. Light can modulate the gating effect of the device and change the transfer characteristic curve from unipolar to ambipolar. This photoswitching in turn produces a significantly improved photocurrent signal. The introduction of an ultrathin Al2O3 interlayer also enables the phototransistor to achieve a responsivity in excess of 105 A/W, a 3 dB bandwidth of 100 kHz, a gain-bandwidth product of 9.14 × 1010 s-1, and a specific detectivity of 1.91 × 1013 Jones. This device architecture enables the gain-bandwidth trade-off in current field-effect phototransistors to be overcome, demonstrating the feasibility of simultaneous high-gain and fast-response photodetection.

Chiral photocurrent in a Quasi-1D TiS3 (001) phototransistor

The presence of in-plane chiral effects, hence spin–orbit coupling, is evident in the changes in the photocurrent produced in a TiS3(001) field-effect phototransistor with left versus right circularly polarized light. The direction of the photocurrent is protected by the presence of strong spin–orbit coupling and the anisotropy of the band structure as indicated in NanoARPES measurements. Dark electronic transport measurements indicate that TiS3 is n-type and has an electron mobility in the range of 1–6 cm2V−1s−1. I–V measurements under laser illumination indicate the photocurrent exhibits a bias directionality dependence, reminiscent of bipolar spin diode behavior. Because the TiS3 contains no heavy elements, the presence of spin–orbit coupling must be attributed to the observed loss of inversion symmetry at the TiS3(001) surface.

Isotope Engineered Fluorinated Single and Bilayer Graphene: Insights into Fluorination Selectivity, Stability, and Defect Passivation.

Tailoring the physicochemical properties of graphene through functionalization remains a major interest for next-generation technological applications. However, defect formation due to functionalization greatly endangers the intrinsic properties of graphene, which remains a serious concern. Despite numerous attempts to address this issue, a comprehensive analysis has not been conducted. This work reports a two-step fluorination process to stabilize the fluorinated graphene and obtain control over the fluorination-induced defects in graphene layers. The structural, electronic and isotope-mass-sensitive spectroscopic characterization unveils several not-yet-resolved facts, such as fluorination sites and CF bond stability in partially-fluorinated graphene (F-SLG). The stability of fluorine has been correlated to fluorine co-shared between two graphene layers in fluorinated-bilayer-graphene (F-BLG). The desorption energy of co-shared fluorine is an order of magnitude higher than the CF bond energy in F-SLG due to the electrostatic interaction and the inhibition of defluorination in the F-BLG. Additionally, F-BLG exhibits enhanced light-matter interaction, which has been utilized to design a proof-of-concept field-effect phototransistor that produces high photocurrent response at a time <200 µs. Thus, the study paves a new avenue for the in-depth understanding and practical utilization of fluorinated graphenic carbon.

Binder polymer influence on the electrical and UV response of organic field-effect transistors

Organic field-effect transistors (OFETs) and phototransistors using blends of Ph-BTBT-10 with binding polymers are prepared. We show that tuning the nature of the polymer is a useful tool to optimise the OFET performance and photoresponsivity.

α-In2O3 monolayer: A promising material as field-effect phototransistor and out-of-plane piezoelectric device

Two-dimensional (2D) semiconductors have opened promising avenues for designing advanced functional devices due to their novel electronic features. In this work, the 2D α-In2O3 monolayer is systematically studied using first-principles calculations. Our calculations show that the α-In2O3 monolayer exhibits a stable configuration with good oxidation resistance. The electronic structure calculations identify that α-In2O3 monolayer is a semiconductor with a direct bandgap of 1.41 eV, which makes the α-In2O3 monolayer to be as a promising candidate in modern bottom/top gate technologies. Interestingly, the partial charge density shows that the valence band maximum and conduction band minimum locate at the different atomic region, and the electron carrier mobility of the α-In2O3 monolayer is much larger than hole carrier mobility, indicating that the electrons and holes can be effectively separated. Additionally, the α-In2O3 monolayer has excellent optical absorption coefficient among the infrared and visible range. Hence, the α-In2O3 monolayer can be used as field-effect phototransistor. Moreover, the asymmetric atomic-layer configuration and strong inner covalent bond of the α-In2O3 monolayer induce a superior out-of-plane piezoelectric response (e31 = 1.81 × 10-10C·m−1, d31 = -0.89 pm·V−1), make α-In2O3 monolayer as a promising material as out-of-plane piezoelectric device.

ReS2 Nanosheet-Based Channels for Two-Dimensional Field Effect Transistors and Phototransistors with High Photoresponsivity

ReS₂ Nanosheet-Based Channels for Two-Dimensional Field Effect Transistors and Phototransistors with High Photoresponsivity

Investigation of β-Gallium oxide based tunnel field effect phototransistor for solar blind UV detection

In this study, a novel β-Ga2O3 based Tunnel field effect phototransistor (Ga2O3-TFET) has been explored and proposed for detection of solar blind UV radiations. β-Ga2O3 owes the advantage of being an effective photoabsorber material for detecting solar blind radiations and rejecting wavelengths outside this range under the application of high voltage requirements. Hence, for the first time β-Ga2O3 along with TFET has been investigated to reduce the required bias voltages with steep switching characteristics from dark state to illuminated state and ultrahigh photoresponsivity. Moreover, Thickness optimization of Ga2O3 plays a vital role for the proposed phototransistor since the photogeneration inside the Ga2O3 develops an effective optical voltage for the operation of the device. Consequently, small dark current of (8.9310−16 A/µm), less required bias voltage (1.19 V), ultrahigh photosensitivity (1.17 ×1011), high responsivity (1.046 ×105 A/W) and detectivity (2.01 ×1017 Jones) at an optimized thickness of 90 nm has been observed. The dynamic characteristics of the proposed phototransistor show a low response time of 5 ms that would promote its development for detection of solar blind UV radiation.

High photoresponsivity in CH3NH3PbI3-XClx perovskite vertical field effect photo transistors

The synthesis of organic-inorganic hybrid perovskites has greatly facilitated the development of high-performance optoelectronic devices such as photovoltaics, light-emitting diodes, lasers, and photodetectors. We report a CH3NH3PbI3-xClx vertical-structure field-effect phototransistor (VFEPT) using Au/Ag NWs as transparent source electrode (TSE) and exhibiting wideband absorption in the 380 to 800 nm range. Due to the ultra-short channel (78 nm) of VFEPT, multiple circulating holes in laser-induced electron-hole pairs, thus achieving excellent photoconductivity. We further tested the photoelectric performance of VFEPT, which showed that the device had the responsivity (R) is 82.99A/W, the external quantum efficiency (EQE) is 3.3 × 104% and the specific detectivity (D*) is 1.86 × 1012 Jones at VG = -2V, VSD = −5V. When VG = 2.5 V, VSD = 5 V, R reaches 109.15 A/W, EQE reaches 3.3 × 104% and D* reaches 2.45 × 1012 Jones. Organic-inorganic hybrid perovskites provide a new approach for high-performance vertical-structured ultra-short channel perovskite photodetectors.

Effective integration of a MOSFET phototransistor to a GaN LED for UV sensing.

In this Letter, we report an effective monolithic integration of a metal oxide semiconductor field effect (MOSFET) phototransistor (PT) and a light-emitting diode (LED) on a GaN-on-Si LED epitaxial (epi) wafer. Avoiding additional growth or Si diffusion, the PT was directly fabricated on the LED epi layer, providing a cost-effective and facile method. As a driver, the PT could modulate both peak value of the light intensity and output current of the integrated LED. As an ultraviolet (UV) detector, our PT showed sufficient responsivity. It was found that the gate-voltage-dependent photocurrent-response of the device had a shorter response time, and a higher responsivity was obtained at a higher gate-voltage bias. The device demonstrated a switching effect that the photoinduced current from the PT drove the LED when the UV lamp was turned on, whereas the photoinduced current stopped driving upon powering off the UV lamp. The experiment proved that the integrated device working as a UV detector exhibited a fast response time and a longstanding stability. We anticipate that such an approach could have potential applications for UV light detection and visible light communication (VLC).

Role of Junctionless Mode in Improving the Photosensitivity of Sub-10 nm Carbon Nanotube/Nanoribbon Field-Effect Phototransistors: Quantum Simulation, Performance Assessment, and Comparison.

In this article, ultrascaled junctionless (JL) field-effect phototransistors based on carbon nanotube/nanoribbons with sub-10 nm photogate lengths were computationally assessed using a rigorous quantum simulation. This latter self-consistently solves the Poisson equation with the mode space (MS) non-equilibrium Green’s function (NEGF) formalism in the ballistic limit. The adopted photosensing principle is based on the light-induced photovoltage, which alters the electrostatics of the carbon-based junctionless nano-phototransistors. The investigations included the photovoltage behavior, the I-V characteristics, the potential profile, the energy-position-resolved electron density, and the photosensitivity. In addition, the subthreshold swing–photosensitivity dependence as a function of change in carbon nanotube (graphene nanoribbon) diameter (width) was thoroughly analyzed while considering the electronic proprieties and the quantum physics in carbon nanotube/nanoribbon-based channels. As a result, the junctionless paradigm substantially boosted the photosensitivity and improved the scaling capability of both carbon phototransistors. Moreover, from the point of view of comparison, it was found that the junctionless graphene nanoribbon field-effect phototransistors exhibited higher photosensitivity and better scaling capability than the junctionless carbon nanotube field-effect phototransistors. The obtained results are promising for modern nano-optoelectronic devices, which are in dire need of high-performance ultra-miniature phototransistors.