Heterostructure Phototransistor Research Articles

Record-High Work-Function p-Type CuBiP2 Se6 Atomic Layers for High-Photoresponse van der Waals Vertical Heterostructure Phototransistor.

The notable lack of intrinsic p-type 2D layered semiconductors has hindered the engineering of 2D devices for complementary metal oxide semiconductors (CMOSs). Herein, a novel quaternary intrinsic p-type 2D semiconductor, CuBiP2 Se6 atomic layers, is introduced intothe2D family. The semiconductor displays a high work function of 5.26eV, a moderate hole mobility of 1.72 cm2 V-1 s-1 , and an ultrahigh on/off current exceeding 106 at room temperature. To date, 5.26eV is the highest work-function recorded in p-type 2D materials, indicating the ultrastable p-type behavior of CuBiP2 Se6 . Additionally, a multilayer graphene/CuBiP2 Se6 /multilayer graphene (MLG/CBPS/MLG)-based fully vertical van der Waals heterostructure phototransistor is designed and fabricated. This device exhibits outstanding optoelectronic performance with a responsivity (R) of 4.9 ×104 A W-1 , an external quantum efficiency (EQE) of 1.5 ×107 %, a detectivity (D) of 1.14 ×1013 Jones, and a broad working wavelength (400-1100nm), respectively. This is comparableto state-of-the-art 2D devices. Such excellent performance is attributed to the ultrashort transmit length and nondestructive/defect-free contacts. This leads to faster response speed and eliminates Fermi-levelpinningeffects. Moreover, ultrahigh responsivity and detectivity endow the device with applaudable imaging sensing capability. These results make CuBiP2 Se6 an ideal p-type candidate material for next-generation CMOSs logic devices.

Near-UV Phototransistors Based on an All-Inorganic Lead-Free Cs3Cu2I5/CuTCNQ Hierarchical Heterostructure

With the rapid advances in metal halide perovskite optoelectronics, eliminating toxic lead from perovskites has been an urgent demand. However, state-of-the-art lead-free perovskite photodetectors are still challenged with issues of low photoresponse, poor stability, etc. Here, all-inorganic lead-free perovskite (Cs3Cu2I5) single crystals that possess good stability under air exposure are synthesized via a facile solid reaction method. Meanwhile, a higher photoluminescence quantum yield of 95.2% and a prolonged carrier lifetime of 1.127 μs are obtained by further optimizing the synthesis. Benefiting from the polyporous surface and hollow structure of Cu-7,7,8,8-tetracyanoquinodimethane (CuTCNQ) microtubes, more Cs3Cu2I5 nanocrystals can adhere on the innershell and outershell of CuTCNQ-15 microtubes. This unique structure contributes to the improved efficiency of utilizing incident light and promotes charge carrier generation and transportation. As a result, the hierarchical CuTCNQ/Cs3Cu2I5 (hollow microtube/nanocrystal) heterostructure phototransistor exhibits a high responsivity of 88.36 A W-1 and a large detectivity of 1.66 × 1012 Jones. The proposed lead-free perovskites and mixed-dimensional heterojunctions are promising for sensitive light detection.

Nonvolatile van der Waals Heterostructure Phototransistor for Encrypted Optoelectronic Logic Circuit.

With the rising demand for information security, there has been a surge of interest in harnessing the intrinsic physical properties of device for designing a secure logic circuit. Here we provide an innovative approach to realize the secure optoelectronic logic circuit based on nonvolatile van der Waals (vdW) heterostructure phototransistors. The phototransistors comprising WSe2 and h-BN flakes exhibit electrical tunability of nonvolatile conductance under cooperative operations of electrical and light stimulus. This intriguing feature allows the phototransistor to work as a building block for the design of secure optoelectronic logic circuit in which the information encryption can be directly achieved with a designed secret key. On the basis of this approach, we assemble two phototransistors into an optoelectronic hybrid circuit and implement a functionally complete set of logic gates (i.e., NOR, XOR, and NAND) in a reconfigurable manner. Our findings highlight the potential of nonvolatile phototransistors for the development of reconfigurable secure optoelectronic circuits.

Large-Area Pixelized Optoelectronic Neuromorphic Devices with Multispectral Light-Modulated Bidirectional Synaptic Circuits.

The complete hardware implementation of an optoelectronic neuromorphic computing system is considered as one of the most promising solutions to realize energy-efficient artificial intelligence. Here, a fully light-driven and scalable optoelectronic neuromorphic circuit with metal-chalcogenide/metal-oxide heterostructure phototransistor and photovoltaic divider is proposed. To achieve wavelength-selective neural operation and hardware-based pattern recognition, multispectral light modulated bidirectional synaptic circuits are utilized as an individual pixel for highly accurate and large-area neuromorphic computing system. The wavelength selective control of photo-generated charges at the heterostructure interface enables the bidirectional synaptic modulation behaviors including the excitatory and inhibitory modulations. More importantly, a 7 × 7 neuromorphic pixel circuit array is demonstrated to show the viability of implementing highly accurate hardware-based pattern training. In both the pixel training and pattern recognition simulation, the neuromorphic circuit array with the bidirectional synaptic modulation exhibits lower training errors and higher recognition rates, respectively.

In₂Se₃/Silicon-on-Insulator Heterojunction Phototransistor for Low Noise Dual-Band Detection

In this study, high-performance In2Se3/Silicon-on-Insulator (SOI) heterojunction field-effect transistor photodetector is fabricated. The In2Se3/Si heterostructure phototransistor exhibits dual-band detection with a maximum responsivity of 12 A/W and 41 A/W for illumination of 405 nm and 800 nm wavelengths, respectively. This phototransistor has shown a lower noise-equivalent power of 6.8 fW.Hz $^{-1/2}$ and higher detectivity of $2.9\times 10^{13}$ cm.Hz $^{1/2}\text{W}^{-1}$ . Flicker noise dominates the In2Se3/SOI phototransistor with a corner frequency of 3 Hz. The device’s enhanced performance is due to the improved synergistic effect with efficient electron-hole dissociation in the heterojunction. This heterostructure based photodetector can be of great interest for dual-band (Ultra-violet and visible) detection in imaging, optical communication and healthcare applications.

Fabrication of a γ-In2Se3/Si heterostructure phototransistor for heart rate detection

A γ-In2Se3/Si heterostructure phototransistor presents a high responsivity arising from the photogating effect. It shows potential applications in real-time and accurate health monitoring, such as heart rate detection.

Enhanced photoresponse of TiO2/MoS2 heterostructure phototransistors by the coupling of interface charge transfer and photogating

Two-dimensional (2D) MoS2 with appealing physical properties is a promising candidate for next-generation electronic and optoelectronic devices, where the ultrathin MoS2 is usually laid on or gated by a dielectric oxide layer. The oxide/MoS2 interfaces widely existing in these devices have significant impacts on the carrier transport of the MoS2 channel by diverse interface interactions. Artificial design of the oxide/MoS2 interfaces would provide an effective way to break through the performance limit of the 2D devices but has yet been well explored. Here, we report a high-performance MoS2-based phototransistor with an enhanced photoresponse by interfacing few-layer MoS2 with an ultrathin TiO2 layer. The TiO2 is deposited on MoS2 through the oxidation of an e-beam-evaporated ultrathin Ti layer. Upon a visible-light illumination, the fabricated TiO2/MoS2 phototransistor exhibits a responsivity of up to 2,199 A/W at a gate voltage of 60 V and a detectivity of up to 1.67 × 1013 Jones at a zero-gate voltage under a power density of 23.2 µW/mm2. These values are 4.0 and 4.2 times those of the pure MoS2 phototransistor. The significantly enhanced photoresponse of TiO2/MoS2 device can be attributed to both interface charge transfer and photogating effects. Our results not only provide valuable insights into the interactions at TiO2/MoS2 interface, but also may inspire new approach to develop other novel optoelectronic devices based on 2D layered materials.

Importance of separating contacts from the photosensitive layer in heterojunction phototransistors

Abstract — We simulate the detection of light in solution-processed poly(3-hexylthiophene) (P3HT)-capped indium oxide (In 2 O 3 ) phototransistors with and without direct electrical contact between the P3HT and the source and drain contacts. Under illumination, the photogenerated carriers enhance the drain current of the transistor, enabling photodetection. We demonstrate improved phototransistor performance by eliminating direct electrical contact between the P3HT and the source and drain contacts due to the inhibition of hole current flow between the contacts in the off-state. The photoresponsivity and detectivity are improved by up to 2.5 and 7 orders of magnitude, respectively, and reach a maximum of 4.4 A/W and 8.7 × 10 17 Jones. Photodetection down to incident light powers as low as 5 pW/cm 2 is possible in the absence of direct contacts while detection is limited to 50 μW/cm 2 otherwise. We determine the photoresponse rise and fall time as 0.4 μs and 0.6 μs, respectively. Our study highlights the importance of using source/drain contacts that are separated from the photosensitive layer to realize optimal phototransistor performance. • Heterostructure phototransistor performance improved. • Off-state current reduced by 9 orders of magnitude. • Photodetectivity improved by 7 orders of magnitude. • Photodetection to powers as low as 5 pW/cm 2 .

Flexible Quasi-2D Perovskite/IGZO Phototransistors for Ultrasensitive and Broadband Photodetection.

Organic-inorganic hybrid perovskites (PVKs) have recently emerged as attractive materials for photodetectors. However, the poor stability and low electrical conductivity still restrict their practical utilization. Owing to the quantum-well feature of two-dimensional (2D) Ruddlesden-Popper PVKs (2D PVKs), a promising quasi-2D PVK/indium gallium zinc oxide (IGZO) heterostructure phototransistor can be designed. By using a simple ligand-exchange spin-coating method, quasi-2D PVK fabricated on flexible substrates exhibits a desirable type-II energy band alignment, which facilitates effective spatial separation of photoexcited carriers. The device exhibits excellent photoresponsivity values of >105 A W-1 at 457 nm, and broadband photoresponse (457-1064 nm). By operating the device in the depletion regime, the specific detectivity is found to be 5.1 × 1016 Jones, which is the record high value among all PVK-based photodetectors reported to date. Due to the resistive hopping barrier in the quasi-2D PVK, the device can also work as an optoelectronic memory for near-infrared information storage. More importantly, the easy manufacturing process is highly beneficial, enabling large-scale and uniform quasi-2D PVK/IGZO hybrid films for detector arrays with outstanding ambient and operation stabilities. All these findings demonstrate the device architecture here provides a rational avenue to the design of next-generation flexible photodetectors with unprecedented sensitivity.

Narrow‐Band QD‐Enhanced PIN Metal‐Oxide Heterostructure Phototransistor with the Assistance of Printing Processes

AbstractInfrared (IR) phototransistors are important building blocks for the true integration of flat‐panel optoelectronic detectors. Although significant progress is made in obtaining an InGaZnO active layer with IR response, the utilization of a high‐performance detector still has many challenges due to low efficiency, high power consumption, and lagging detection speed. Herein, a positive‐intrinsic‐negative (PIN) heterostructure phototransistor directly modulating the charges' transfer barrier with low power consumption (1 nW), high efficiency (EQE > 700%), a 200 Hz detecting bandwidth, and high detectivity (1 × 1011 cm Hz1/2 W−1) at an IR wavelength (1.5 µm in the high‐frequency circumstance) is demonstrated. These excellent sensing properties of the PIN phototransistor, together with its advantages of low power consumption and versatility, make the use of a heterostructure a powerful strategy for the development of on‐chip optoelectronic detectors.

Phototransistors with Negative or Ambipolar Photoresponse Based on As‐Grown Heterostructures of Single‐Walled Carbon Nanotube and MoS2

AbstractA facile synthesis method for the heterostructures of single‐walled carbon nanotubes (SWCNTs) and few‐layer MoS2 is reported. The heterostructures are realized by in situ chemical vapor deposition of MoS2 on individual SWCNTs. Field effect transistors based on the heterostructures display different transfer characteristics depending on the formation of MoS2 conduction channels along SWCNTs. Under light illumination, negative photoresponse originating from charge transfer from MoS2 to SWCNT is observed while positive photoresponse is observed in MoS2 conduction channels, leading to ambipolar photoresponse in devices with both SWCNT and MoS2 channels. The heterostructure phototransistor, for negative photoresponse, exhibits high responsivity (100–1000 AW−1) at low bias voltages (0.1 V) in the visible spectrum (500–700 nm) by combining high mobility conduction channel (SWCNT) with efficient light absorber (MoS2).

Ultrasensitive Heterojunctions of Graphene and 2D Perovskites Reveal Spontaneous Iodide Loss

Summary Despite the demonstrated high efficiency of perovskite solar cells and light-emitting devices, the understanding of the intrinsic stability of perovskites is far from complete. In this work, using an ultrasensitive, exfoliated 2D perovskite single-crystal sheet/graphene heterostructure device, we reveal spontaneous iodide loss as an important degradation pathway of 2D perovskite single crystals, which n-dopes the perovskite semiconductor by generating positively charged iodide vacancies. Furthermore, we show that covering perovskites with graphene can suppress the iodide loss, significantly improving perovskite stability. A perovskite phototransistor is demonstrated with a graphene/2D perovskite/graphene structure, which shows no degradation after 75 days. Our work not only provides important insights for future stable perovskite optoelectronic device development, but also demonstrates the potential of graphene as a promising sensitive diagnostic tool for device and material degradation studies.

Highly Efficient and Air-Stable Infrared Photodetector Based on 2D Layered Graphene-Black Phosphorus Heterostructure.

The presence of a direct band gap and high carrier mobility in few-layer black phosphorus (BP) offers opportunities for using this material for infrared (IR) light detection. However, the poor air stability of BP and its large contact resistance with metals pose significant challenges to the fabrication of highly efficient IR photodetectors with long lifetimes. In this work, we demonstrate a graphene-BP heterostructure photodetector with ultrahigh responsivity and long-term stability at IR wavelengths. In our device architecture, the top layer of graphene functions not only as an encapsulation layer but also as a highly efficient transport layer. Under illumination, photoexcited electron-hole pairs generated in BP are separated and injected into graphene, significantly reducing the Schottky barrier between BP and the metal electrodes and leading to efficient photocurrent extraction. The graphene-BP heterostructure phototransistor exhibits a long-term photoresponse at near-infrared wavelength (1550 nm) with an ultrahigh photoresponsivity (up to 3.3 × 103 A W-1), a photoconductive gain (up to 1.13 × 109), and a rise time of about 4 ms. Considering the thickness-dependent band gap in BP, this material represents a powerful photodetection platform that is able to sustain high performance in the IR wavelength regime with potential applications in remote sensing, biological imaging, and environmental monitoring.

ZrO2 quantum dots/graphene phototransistors for deep UV detection

ZrO2 is a promising material for deep-UV detection application, yet the low carrier density and high crystal lattice defects hinder the device performance. Graphene is an attractive material for photoactive and charge transport layers in photodetectors, but the photoresponsivity have been limited by the weak light absorption, no wavelength selectivity. Here, we demonstrate heterostructure phototransistors consist of graphene as the conducting channel, which is covered by a film of ZrO2 quantum dots as the light absorption layer. Light absorption in the quantum dots layer creates electron-hole pairs. Under the built-in electric field, the electrons are trapped in ZrO2 acting as an additional light tunable gate, whereas the holes are transferred towards the graphene. The ZnO2/Graphene heterostructure, with a high photoresponsivity of 22AW−1 and wavelength selectivity to deep UV wavelength range (220–250nm) at low operating voltage, is promising to be integrated into solution processed and low-cost optoelectrical devices.

Large-Scale Synthesis of a Uniform Film of Bilayer MoS2 on Graphene for 2D Heterostructure Phototransistors

The large-scale synthesis of atomically thin, layered MoS2/graphene heterostructures is of great interest in optoelectronic devices because of their unique properties. Herein, we present a scalable synthesis method to prepare centimeter-scale, continuous, and uniform films of bilayer MoS2 using low-pressure chemical vapor deposition. This growth process was utilized to assemble a heterostructure by growing large-scale uniform films of bilayer MoS2 on graphene (G-MoS2/graphene). Atomic force microscopy, Raman spectra, and transmission electron microscopy characterization demonstrated that the large-scale bilayer MoS2 film on graphene exhibited good thickness uniformity and a polycrystalline nature. A centimeter-scale phototransistor prepared using the G-MoS2/graphene heterostructure exhibited a high responsivity of 32 mA/W with good cycling stability; this value is 1 order of magnitude higher than that of transferred MoS2 on graphene (2.5 mA/W). This feature results from efficient charge transfer at the interface enabled by intimate contact between the grown bilayer MoS2 (G-MoS2) and graphene. The ability to integrate multilayer materials into atomically thin heterostructures paves the way for fabricating multifunctional devices by controlling their layer structure.

MoS2-InGaZnO Heterojunction Phototransistors with Broad Spectral Responsivity.

We introduce an amorphous indium-gallium-zinc-oxide (a-IGZO) heterostructure phototransistor consisting of solution-based synthetic molybdenum disulfide (few-layered MoS2, with a band gap of ∼1.7 eV) and sputter-deposited a-IGZO (with a band gap of ∼3.0 eV) films as a novel sensing element with a broad spectral responsivity. The MoS2 and a-IGZO films serve as a visible light-absorbing layer and a high mobility channel layer, respectively. Spectroscopic measurements reveal that appropriate band alignment at the heterojunction provides effective transfer of the visible light-induced electrons generated in the few-layered MoS2 film to the underlying a-IGZO channel layer with a high carrier mobility. The photoresponse characteristics of the a-IGZO transistor are extended to cover most of the visible range by forming a heterojunction phototransistor that harnesses a visible light responding MoS2 film with a small band gap prepared through a large-area synthetic route. The MoS2-IGZO heterojunction phototransistors exhibit a photoresponsivity of approximately 1.7 A/W at a wavelength of 520 nm (an optical power of 1 μW) with excellent time-dependent photoresponse dynamics.

Optimization of InP–InGaAs HPT Gain: Design of an Opto-Microwave Monolithic Amplifier

We have designed an opto-microwave monolithic amplifier with emphasis on the definition of the opto-microwave power gain. First, we present physical simulations of an InP-InGaAs heterostructure phototransistor (HPT), which enable the structural analysis of the composition and behavior of the phototransistor. From these simulations and from both electrical and optical measurements, we next established a large-signal model, which adds photoelectric effect to an HBT model. Small-signal opto-microwave S-parameters of the HPT are first defined and then related to the small-signal opto-microwave power gain of the phototransistor. Relations are given to enable optimum loads on the base and collector ports to be found so that the opto-microwave gain can be optimized. An opto-microwave amplifier is then designed, realized, and measured with a setup based on the beating of two lasers.

Low-power phototransceiver arrays with vertically integrated resonant-cavity LEDs and heterostructure phototransistors

Low-power phototransceivers and phototransceiver arrays, with vertically integrated high-gain heterojunction phototransistors (HPTs) and resonant-cavity light-emitting diodes (RCLEDs), are demonstrated. A tunnel junction was used as a low resistance interconnect between the two devices. The input and output wavelengths are 0.63-0.85 and 0.98 μm, respectively. The phototransceiver exhibits an optical gain of 13 dB and power dissipation of 400 μW for an input power of 5 μW. The phototransceiver arrays demonstrate good uniformity, low optical crosstalk, and imaging capabilities.

Si-BASED OPTOELECTRONIC DEVICES AND THEIR ATTRACTIVE APPLICATIONS*)

The semiconductor photonics and optoelectronics which have a great significance in the development of advanced high technology of information systems will be discussed in this paper. The emphasis will be put on the recent research carried out in our laboratory in enhanced luminescence from low dimensional materials such as SiGe/Si and Er-doped Si-rich SiO2/Si and Er-doped SixNy/Si. A ring shape waveguide structure, used to promote the effective absorption coefficient in PIN photodetector for 1.3 mu m wavelength and a resonant cavity enhanced structure, used to improve the quantum efficiency and response in heterostructure photo-transistor (HPT), are also proposed in this paper.

Optoelectronic data filter for selection and projection

Database processing, like the majority of nonnumerical applications, exhibits a high degree of functional parallelism but does not require complex operations; therefore it is amenable to optical solutions. The architecture of an optoelectronic filter that is capable of performing selection and projection operations on a two-dimensional data array in a relational database environment is presented. The system receives input from a parallel optical memory, one page at a time, and performs logic operations by using optoelectronic smart pixels based on heterostructure phototransistors and vertical-cavity surfaceemitting lasers. Combinations of AND and XOR gates are used to realize row-lcolumn masking and comparisons of input data against user-supplied search arguments. The main goal of the filter is to reduce the effective data rate between the highly parallel optical storage and the low input data rate conventional electronic computer, thus efficiently interfacing currently available photonic and electronic technologies.