Heterojunction Phototransistor Research Articles

A Dual Mode MoTe2/WS2/WSe2 Double Van der Waals Heterojunctions Phototransistor for Optical Imaging and Communication

AbstractVan der Waals (vdW) heterostructures, formed by stacking different two‐dimensional (2D) materials, have emerged as a promising platform for next‐generation optoelectronic devices through band engineering. While various all‐2D and mixed‐dimensional heterojunction phototransistors based on p–n junctions or Schottky junctions have been developed, their performance, often constrained by the trade‐off between responsivity (R) and response speed, limits their widespread application. Here, a dual‐mode phototransistor based on a MoTe2/WS2/WSe2 double vdW heterostructure is designed. The bottom WSe2 layer effectively modulates the entire MoTe2/WS2 heterojunction channel, enabling both photoconductive and photovoltaic modes with exceptional optoelectronic properties in a single device. Specifically, the proposed device exhibits a maximum R of 2540 A W−1 and an impressive specific detectivity of 8 × 1012 Jones under the photoconductive mode. Under the photovoltaic mode, it achieves a fast response speed of 35.3/49.1 µs and a high light on/off ratio of 2 × 105. Additionally, the device exhibits latent potential for high‐resolution imaging across various wavelengths and fast optical communication. This work offers a rational alternative for achieving dual‐mode photodetection and highlights its promising application prospects in imaging and optical communication.

Electrically Tunable Multiple-Effects Synergistic and Boosted Photoelectric Performance in Te/WSe2 Mixed-Dimensional Heterojunction Phototransistors.

Mix-dimensional heterojunctions (MDHJs) photodetectors (PDs) built from bulk and 2D materials are the research focus to develop hetero-integrated and multifunctional optoelectronic sensor systems. However, it is still an open issue for achieving multiple effects synergistic characteristics to boost sensitivity and enrich the prospect in artificial bionic systems. Herein, electrically tunable Te/WSe2 MDHJs phototransistors are constructed, and an ultralow dark current below 0.1pA and a large on/off rectification ratio of 106 is achieved. Photoconductive, photovoltaic, and photo-thermoelectric conversions are simultaneously demonstrated by tuning the gate and bias. By these synergistic effects, responsivity and detectivity respectively reach 13.9 AW-1 and 1.37×1012 Jones with 400 times increment. The Te/WSe2 MDHJs PDs can function as artificial bionic visual systems due to the comparable response time to those of the human visual system and the presence of transient positive and negative response signals. This work offers an available strategy for intelligent optoelectronic devices with hetero-integration and multifunctions.

Organic Heterojunction Phototransistors with Bi‐Directional Photoresponse for Vision Biomimetics

AbstractThe scientific community is very interested in artificial visual perception systems because of their neuromorphological capabilities, such as image recognition, learning, and memory. This study reports on an organic heterojunction ambipolar transistor with PTCDI‐C8/C8‐BTBT/PTCDI‐C8 sandwich structure. The proposed transistor efficiently transports both holes and electrons, with a current‐on‐switch ratio of ≈106. Furthermore, hole or electron carrier transmission mechanisms are constructed to achieve the controllable adjustment of bi‐directional photoresponse under identical light illumination conditions by adjusting the gate voltage (positive photoresponse for Vg = 30 V and negative photoresponse for Vg = −30 V). The basic synaptic behaviors are simulated under light illumination, and the power consumption of the device is 18.51 fJ per synaptic event, which is comparable to the energy required for biological synapses. Finally, the simulation of human visual adaptation is completed using the bi‐directional photoresponse effects of the organic heterojunction phototransistor array, which provides a novel idea for neuromorphic visual simulation.

Optimum Ge Profile Design for High-Response SiGe/Si Heterojunction Phototransistor Applicable in Wide Spectral Range of 400–1000 nm

Optimum Ge Profile Design for High-Response SiGe/Si Heterojunction Phototransistor Applicable in Wide Spectral Range of 400–1000 nm

Spacer Engineering Enables Fine‐Tuned Thin Film Microstructure and Efficient Charge Transport for Ultrasensitive 2D Perovskite‐Based Heterojunction Phototransistors and Optoelectronic Synapses

Abstract2D Ruddlesden–Popper phase layered perovskites (RPLPs) hold great promise for optoelectronic applications. In this study, a series of high‐performance heterojunction phototransistors (HPTs) based on RPLPs with different organic spacer cations (namely butylammonium (BA+), cyclohexylammonium (CyHA+), phenethylammonium (PEA+), p‐fluorophenylethylammonium (p‐F‐PEA+), and 2‐thiophenethylammonium (2‐ThEA+)) are fabricated successfully, in which high‐mobility organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b]benzothiophene is adopted to form type II heterojunction channels with RPLPs. The 2‐ThEA+‐RPLP‐based HPTs show the highest photosensitivity of 3.18 × 107 and the best detectivity of 9.00 × 1018 Jones, while the p‐F‐PEA+‐RPLP‐based ones exhibit the highest photoresponsivity of 5.51 × 106 A W−1 and external quantum efficiency of 1.32 × 109%, all of which are among the highest reported values to date. These heterojunction systems also mimicked several optically controllable fundamental characteristics of biological synapses, including excitatory postsynaptic current, paired‐pulse facilitation, and the transition from short‐term memory to long‐term memory states. The device based on 2‐ThEA+‐RPLP film shows an ultra‐high PPF index of 234%. Moreover, spacer engineering brought fine‐tuned thin film microstructures and efficient charge transport/transfer, which contributes to the superior photodetection performance and synaptic functions of these RPLP‐based HPTs. In‐depth structure‐property correlations between the organic spacer cations/RPLPs and thin film microstructure/device performance are systematically investigated.

High‐Performance N‐MoSe2/P‐GeSn/N‐Ge van der Waals Heterojunction Phototransistor for Short‐Wave Infrared Photodetection

AbstractIn this work, a high‐performance two‐terminal n‐MoSe2/p‐GeSn/n‐Ge van der Waals (vdW) heterojunction phototransistor (HPT) is proposed and demonstrated for short‐wave infrared (SWIR) detection. With a high Sn content of 17.1% in the GeSn base region, the cutoff wavelength is extended to beyond 2400 nm. The substantial electron/hole injection ratio resulting from the large bandgap offset between the MoSe2 emitter and the GeSn base enables the harvesting of high photocurrent gain. A record high responsivity of 12.75 A W−1 and an excellent specific detectivity of 1.74 × 1010 Jones at 2250 nm are achieved under a collector‐emitter bias of 1.0 V at room temperature. A response time of 462 µs at 1550 nm outbalancing that of most vdW junction‐based devices is obtained for the non‐optimized devices. Those results show that the mixed‐dimensional GeSn HPT is one of the promising candidates for detection of infrared band above 2 µm.

High Current Operation in Type-II InP/GaAsSb/InGaAs Double Heterojunction Phototransistors

High Current Operation in Type-II InP/GaAsSb/InGaAs Double Heterojunction Phototransistors

Visible to Short‐Wave Infrared Broadband p‐WSe2/n‐Ge Heterojunction Phototransistor with an Annular Shallow‐Trench Schottky Barrier Collector

Van der Waals (vdW) heterostructures based on two‐dimensional materials and conventional group IV semiconductors have shown great potential for wide spectrum, highly sensitive photodetectors owing to their broadband absorption, high‐quality interface, and compatibility with complementary metal‐oxide‐semiconductor (CMOS) technology. Herein, a unique heterojunction phototransistor composed of an indium tin oxide capped p‐WSe2/n‐Ge vdW heterojunction serving as the emitter and an annular shallow‐trench Al/Ge Schottky junction acting as the collector is proposed. The mixed‐dimensional phototransistor exhibiting high responsivities up to 66 A W−1 at 405 nm and 124 A W−1 at 1,550 nm demonstrates a brilliant wide spectrum response performance. The high photocurrent gain can be attributed to the extra‐large carrier injection ratio of the heterojunction. The short transient response time in the order of 100 μs is achieved with the modified lateral electrical field by the annular shallow‐trench Schottky barrier collector. The combination of p‐WSe2/n‐Ge vdW heterojunction and the annular shallow‐trench Al/n‐Ge Schottky junction renders a low‐cost, high‐performance photodetector fabricated in a simple and CMOS compatible way for visible to short‐wave infrared broadband detection.

Chiroptical Synaptic Heterojunction Phototransistors Based on Self-Assembled Nanohelix of π-Conjugated Molecules for Direct Noise-Reduced Detection of Circularly Polarized Light.

High-performance chiroptical synaptic phototransistors are successfully demonstrated using heterojunctions composed of a self-assembled nanohelix of a π-conjugated molecule and a metal oxide semiconductor. To impart strong chiroptical activity to the device, a diketopyrrolopyrrole-based π-conjugated molecule decorated with chiral glutamic acid is newly synthesized; this molecule is capable of supramolecular self-assembly through noncovalent intermolecular interactions. In particular, nanohelix formed by intertwinded fibers with strong and stable chiroptical activity in a solid-film state are obtained through hydrogen-bonding-driven, gelation-assisted self-assembly. Phototransistors based on interfacial charge transfer at the heterojunction from the chiroptical nanohelix to the metal oxide semiconductor show excellent chiroptical detection with a high photocurrent dissymmetry factor of 1.97 and a high photoresponsivity of 218 A W-1 . The chiroptical phototransistor demonstrates photonic synapse-like, time-dependent photocurrent generation, along with persistent photoconductivity, which is attributed to the interfacial charge trapping. Through the advantage of synaptic functionality, a trained convolutional neural network successfully recognizes noise-reduced circularly polarized images of handwritten alphabetic characters with better than 89.7% accuracy.

Design electrical model noise and perform nonlinearities of SiGe bipolar phototransistor

This study uses a new model developed in this paper to investigate the performance of a heterojunction phototransistor (HPT) on SiGe technology. An electrical model of an optical window phototransistor was developed based on the Ebers & Moll model, and its performance was evaluated by examining the error vector magnitude (EVM) when integrated into a mobile communication setup. Simulations showed that the HPT exhibited an EVM lower than 8%, enabling 64-Quadrature Amplitude Modulation (64-QAM) modulation for the mobile network. The third-order intercept point (IP3) measured 22 dBm, making the HPT suitable for Radio over Fiber (RoF) links in the detection block. The noise model of the HPT was also studied, resulting in a favorable power spectral density (PSD) that facilitates accurate modeling and prediction of the noise behavior of HPTs across various applications. This study provides valuable insights into the performance of HPTs on SiGe technology, enabling the development of more precise and efficient models for future research and practical applications. The results carry significant implications for the use of HPTs in optical communication systems.

Ultrasensitive Phototransistor Based on Laser-Induced P-Type Doped WSe2/MoS2 Van der Waals Heterojunction

Out-of-plane p-n heterojunctions based on two-dimensional layered materials (2DLMs) with unusual physical characteristics are attracting extensive research attention for their application as photodetectors. However, the present fabrication method based on 2DLMs produces out-of-plane p-n homojunction devices with low photoresponsivity and detectivity. This work reports an ultrasensitive phototransistor based on a laser-induced p-doped WSe2/MoS2 van der Waals heterojunction. The laser treatment is used for p-doping WSe2 nanoflakes using high work function WOx. Then, an n-type MoS2 nanoflake is transferred onto the resulting p-doped WSe2 nanoflake. The built-in electric field of p-doped WSe2/MoS2 is stronger than that of pristine WSe2/MoS2. The p-n junction between p-doped WSe2 and MoS2 can separate more photogenerated electron–hole pairs and inject more electrons into MoS2 under laser illumination than pristine WSe2/MoS2. Thus, a high photoresponsivity (R) of ~1.28 × 105 A·W−1 and high specific detectivity (D*) of ~7.17 × 1013 Jones are achieved under the illumination of a 633 nm laser, which is approximately two orders higher than the best phototransistor based on a WSe2/MoS2 heterojunction. Our work provides an effective and simple method to enhance photoresponsivity and detectivity in two-dimensional (2D) heterojunction phototransistors, indicating the potential applications in fabricating high-performance photodetectors based on 2DLMs.

Porous Metal-organic-framework/ReS2 Heterojunction Phototransistor for Polarization-sensitive Visual Adaptation Emulation.

Visual adaptation allows organisms to accurately perceive the external world even in dramatically changing environments, from dim starlight to bright sunlight. In particular, polarization-sensitive visual adaptation can effectively process the polarized visual information that is ubiquitous in nature. However, such an intriguing characteristic still remains to be a great challenge in the semiconductor device. Herein, a novel porous metal-organic-framework phototransistor with anisotropic-ReS2 -based heterojunction is demonstrated for the polarization-sensitive visual adaptation emulation. The device exhibits the intriguing polarized sensitivity and adaptive ability due to its strong anisotropic and trapping-detrapping characteristics, respectively. A series of polarization-sensitive neuromorphic behaviors like polarization-perceptual excitatory postsynaptic current, multimode adjustable dichroic ratio, and reconfigurable sensory adaption, are experimentally demonstrated through this porous heterojunction phototransistor. More importantly, with the polarization-electricity cooperation strategy, the advanced polarization-sensitive visual adaptation with strong bottom-gate control and environment dependence is successfully realized for the first time. These results represent a significant step toward the new generation of intelligent visual perception systems in autonomous navigation and human-machine interaction, etc. This article is protected by copyright. All rights reserved.

Nanographene-Based Heterojunctions for High-Performance Organic Phototransistor Memory Devices.

Organic phototransistors can enable many important applications such as nonvolatile memory, artificial synapses, and photodetectors in next-generation optical communication and wearable electronics. However, it is still a challenge to achieve a big memory window (threshold voltage response ∆Vth ) for phototransistors. Here, a nanographene-based heterojunction phototransistor memory with large ∆Vth responses is reported. Exposure to low intensity light (25.7µWcm-2 ) for 1 s yields a memory window of 35V, and the threshold voltage shift is found to be larger than 140V under continuous light illumination. The device exhibits both good photosensitivity (3.6 × 105 ) and memory properties including long retention time (>1.5 × 105 s), large hysteresis (45.35V), and high endurance for voltage-erasing and light-programming. These findings demonstrate the high application potential of nanographenes in the field of optoelectronics. In addition, the working principle of these hybrid nanographene-organic structured heterojunction phototransistor memory devices is described which provides new insight into the design of high-performance organic phototransistor devices.

High-Performance Solar-Blind UV Phototransistors Based on ZnO/Ga2O3 Heterojunction Channels.

High-performance phototransistor-based solar-blind (200-280 nm) ultraviolet (UV) photodetectors (PDs) are constructed with a low-cost thin-film ZnO/Ga2O3 heterojunction. The optimized PD shows high spectral selectivity (R254/R365 > 1 × 103) with a photo-to-dark current ratio of ∼104, a responsivity of 113 mA/W, a detectivity of 1.25 × 1012 Jones, and a response speed of 41 ms under 254 nm UV light irradiation. It is found that the gate electrode of a three-terminal phototransistor can amplify the responsivity and increase the photo-to-dark current ratio because of the different densities of field-induced electrons at different gate biases. In addition, the built-in electric field at the ZnO/Ga2O3 heterojunction interface can control the distribution of the photoinduced electrons and the total conductivity of the heterojunction, which can further enhance device performance. Together with the simple fabrication process, the achieved results suggest that the three-terminal ZnO/Ga2O3 heterojunction phototransistor is a promising candidate for highly sensitive solar-blind PDs.

Hybrid Interfacial Engineering: An Enabling Strategy for Highly Sensitive and Stable Perovskite Quantum Dots/Organic Heterojunction Phototransistors

All-inorganic lead halide perovskite quantum dots (PQD) have attracted tremendous research interest in the field of phototransistors due to their excellent optoelectronic properties. However, the inefficient charge transport/extraction and high trap-state density of the assembled PQD films seriously limit the photoresponsivity of PQD-based phototransistors. Herein, we demonstrate that these limits can be overcome by adopting a novel device architecture composed of a polar-polymer capping layer on a PQD/organic semiconductor (OSC) heterojunction. The polar polymer film plays the role of both electron trapping and encapsulation, whereas OSC provides the fast transport tracks for charges and PQD serves as the photoactive materials. Owing to the balanced dynamic processes of photogenerated charges, highly sensitive photodetection is achieved, as demonstrated by the peak photosensitivity of 1.5 × 104, a photoresponsivity of 2.1 × 104 A/W, a detectivity of 1 × 1015 Jones, and a high gain of 6.4 × 104 under weak incident light of 3 μW/cm2. Additionally, the phototransistors exhibit superior stability and reproducibility with negligible changes in the output current both in darkness and under illumination after storing for 4 months. The results demonstrate the promising potentials of the polar polymer/PQD/OSC heterojunction for high-performance photodetectors, and the mechanism and strategy described here can be applied to other kinds of quantum dots-based optoelectronic devices.

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.

Ga2O3/GaN-based solar-blind phototransistors fabricated using a thermal oxidation process performed on the GaN p-n junction layers

In this article, β-Ga2O3/GaN-based solar-blind phototransistors are fabricated using a thermal oxidation process performed on the p-GaN layer of a p-GaN/n-GaN junction to form the β-Ga2O3/p-GaN/n-GaN heterostructure. The thermal-oxidized β-Ga2O3 films exhibit a (2̅01)-orientated crystal phase and high-resistivity property. The high-resistivity β-Ga2O3 layer can be converted into an n-type β-Ga2O3 layer through Si ion implantation and a subsequent thermal annealing process. The typical electron concentration and mobility of the Si-implanted β-Ga2O3 are as high as 3.2 × 1020 cm−3 and 177 cm2v−1s−1, respectively. The n-type β-Ga2O3 and unimplanted β-Ga2O3 layers serve as the collector associating with the p-GaN and n-GaN layers, which function as the base and emitter, respectively, to construct the heterojunction phototransistors (HPTs). The HPTs exhibit a distinct cut-off wavelength at around 260 nm, indicating that the photocurrents result from the β-Ga2O3 layers rather than the p-GaN and n-GaN layers. The HPTs also show a significant bias-dependent responsivity in the deep UV (λ < 260 nm) region. This increased responsivity can be attributed to band discontinuity, resulting in the accumulation of photogenerated carriers at the β-Ga2O3/p-GaN interface. The preliminary results suggest that the β-Ga2O3/GaN-based HPTs can be achieved through the thermal oxidation of a p-GaN/n-GaN epitaxial structure.

A SiGe/Si Phototransistor With High FOM of Gain*VA Using 0.35-μm BiCMOS Technology

A novel SiGe/Si phototransistor with high figure of merit (FOM) of gain*early voltage for optical communication was designed and fabricated in a standard 0.35- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> BiCMOS process. A compound base consisting of a P-Si layer and a P+-SiGe layer was designed to achieve a good optical response through relieving the negative influence induced by doped ion’s mutual diffusion in device fabrication. The fabricated surface-illuminated SiGe/Si heterojunction phototransistor (HPT) was measured under 850-nm incident light with a variety of optical powers at 1-V collector bias. When the incident optical power was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.29~\mu \text{W}$ </tex-math></inline-formula> , the collector current reached <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.45~\mu \text{A}$ </tex-math></inline-formula> . The maximum gain exceeded 6.925 with the dark current of about 100 pA. The FOM of gain*early voltage of the proposed SiGe/Si HPT can achieve 100.97. Its optical DC and RF responses under high light power were analyzed with a physically based simulation model, which considered the process effects of device fabrication detailed. The optical gain may promote to 13.3 but with the deteriorated output performance and a smaller early voltage. The maximum optical characteristic frequency may reach 17.6 GHz.

Operation voltage and illumination intensity dependent space-charge limited current conductions in vertical organic phototransistors based on CuPc/C60 heterojunction and graphene

For a trap-free single layer single carrier (hole-only or electron-only) organic device of thickness d, dielectric constant εr, and mobility μ, the relation of current density j with voltage V is described by the well-known Mott–Gurney equation, j=9ε0εrμV2/8d3, which can be rewritten as j=GV, where G=9ε0εrμ/8d3 can be called space-charge limited (SCL) conductance. We investigated the current–voltage characteristics of vertical organic heterojunction phototransistors based on graphene as the source and C60/copper phthalocyanine (CuPc) heterojunction as the photoactive layer. We found that the drain current vs drain voltage (Id-Vd) characteristic is composed of two distinct SCL conductions with SCL-conductance being strongly dependent on the gate voltage and illumination intensity. At low gate voltages, the Id-Vd curve can be divided into two sections of SCL current conduction with different SCL-conductance: the lower conductance in the lower drain voltage range and the higher conductance in the higher drain voltage range. Both low and high SCL-conductance increase with the gate voltage and illumination intensity. However, as the gate voltage increases to a certain threshold, the two SCL sections unify to only one with the conductance being between them. Our findings implicate that the current conduction of an ideal vertical organic phototransistor (VOPT), whose source/organic interface contact is Ohmic and organic semiconductor is trap free, can be well modeled by the SCL conduction theory with carrier density dependent mobility, which is strongly related to the gate voltage and illumination intensity, and that the mobility of VOPTs at a certain gate voltage can be extracted by the Mott–Gurney equation.

Ultrafast and Polarization-Sensitive ReS2/ReSe2 Heterostructure Photodetectors with Ambipolar Photoresponse.

Recently, two-dimensional (2D) van der Waals (vdWs) heterostructures provided excellent and fascinating platforms for advanced engineering in high-performance optoelectronic devices. Herein, novel ReS2/ReSe2 heterojunction phototransistors are constructed and explored systematically that display high responsivity, wavelength-dependent ambipolar photoresponse (negative and positive), ultrafast and polarization-sensitive detection capability. This photodetector exhibits a positive photoresponse from UV to visible spectrum (760 nm) with high photoresponsivities about 126.56 and 16.24 A/W under 350 and 638 nm light illumination, respectively, with a negative photoresponse over 760 nm, which is mainly ascribed to the ambipolar photoresponse modulated by gate voltage. In addition, profound linear polarization sensitivity is demonstrated with a dichroic ratio of about ∼1.2 at 638 nm and up to ∼2.0 at 980 nm, primarily owing to the wavelength-dependent absorption anisotropy and the stagger alignment of the crystal. Beyond static photodetection, the dynamic photoresponse of this vdWs device presents an ultrafast and repeatable photoswitching performance with a cutoff frequency (f3dB) exceeding 100 kHz. Overall, this study reveals the great potential of 2D ReX2-based vdWs heterostructures for high-performance, ultrafast, and polarization-sensitive broadband photodetectors.