RTD/HPT光控单-双稳转换逻辑单元

以光接收器件代替RTD MOBILE(RTD单-双稳转换逻辑单元)电路中的HEMT或HBT,可构成光控MOBILE电路。在比较了四种光控MOBILE结构的基础上,选择RTD/HPT光控结构,重点分析讨论了RTD/HPT光控MOBILE的工作原理,当光控MOBILE的输入光功率超过一个临界值时,MOBILE的输出电压便会从高电平跳变到低电平;由HPT光增益理论分析了提高HPT性能的措施以及HPT设计中应该注意的问题;介绍了以Si光三极管代替HPT,通过模拟实验,验证了RTD/HPT光控MOBILE的逻辑功能。     

Ultra‐Thin Layered Ternary Single Crystals [Sn(SxSe1−x)2] with Bandgap Engineering for High Performance Phototransistors on Versatile Substrates

2D ternary semiconductor single crystals, an emerging class of new materials, have attracted significant interest recently owing to their great potential for academic interest and practical application. In addition to other types of metal dichalcogenides, 2D tin dichalcogenides are also important layered compounds with similar capabilities. Yet, multi‐elemental single crystals enable to assist multiple degrees of freedom for dominant physical properties via ratio alteration. This study reports the growth of single crystals Se‐doped SnS₂ or SnSSe alloys, and demonstrates their capability for the fabrication of phototransistors with high performance. Based on exfoliation from bulk high quality single crystals, this study establishes the characteristics of few‐layered SnSSe in structural, optical, and electrical properties. Moreover, few‐layered SnSSe phototransistors are fabricated on both rigid (SiO₂/Si) and versatile polyethylene terephthalate substrates and their optoelectronic properties are examined. SnSSe as a phototransistor is demonstrated to exhibit a high photoresponsivity of about 6000 A W^?1 with ultra‐high photogain ≈8.8 × 10⁵, fast response time ≈9 ms, and specific detectivity (D*) ≈8.2 × 10¹² J. These unique features are much higher than those of recently published phototransistors configured with other few‐layered 2D single crystals, making ultrathin SnSSe a highly qualified candidate for next‐generation optoelectronic applications.     

光敏三极管响应速度与器件结构参数的关系

对影响光敏三极管光电响应速度的器件结构进行了理论和计算机数值分析。结果表明 ,与基极电阻和电流增益相关的基区宽度是器件优化设计的重点之一。实验结果与分析结果较好一致。选用合适的基区宽度并采取其他措施 ,可使光敏三极管的响应时间降至 0 .6 μs以下。     

The effect of oxygen content on the performance of low-voltage organic phototransistor memory

Optical writing and electrical erasing organic phototransistor memory (OPTM) is a promising photoelectric device for its novel integration of photosensitive and memory properties. The performance of OPTM can be influenced by the trap density of the gate dielectric layer. Here, we occupy tantalum pentoxide (Ta₂O₅), which is a prospective material in microelectronics field, as the gate dielectric. By increasing the oxygen content from 10% to 50% during the fabrication process of Ta₂O₅, it is found that the mobility and the photoresponsivity of OPTMs are significantly enhanced about 10 times and the retention time is greatly increased to 8.4 × 10⁴ s as well. As far as we know, this is the first example that the modulation of oxygen content can improve the OPTM performance. Furthermore, the change of the oxygen content gives rise to the alteration of the threshold voltage and memory window, of which the absolute values of all the threshold voltage are below 5 V which is low enough to reduce the power consumption. It is found that the oxygen content can influence the surface roughness and surface energy of Ta₂O₅ films, which alter the nucleation and orientation of semiconductor layers, change the contact resistance and modulate the electron trap density in the Ta₂O₅ films.     

Large‐Size Growth of Ultrathin SnS2 Nanosheets and High Performance for Phototransistors

2D SnS₂ nanosheets have been attracting intensive attention as one potential candidate for the modern electronic and/or optoelectronic fields. However, the controllable large‐size growth of ultrathin SnS₂ nanosheets still remains a great challenge and the photodetectors based on SnS₂ nanosheets suffer from low responsivity, thus hindering their further applications so far. Herein, an improved chemical vapor deposition route is provided to synthesize large‐size SnS₂ nanosheets, the side length of which can surpass 150 μm. Then, ultrathin SnS₂ nanosheet‐based phototransistors are fabricated, which achieve high photoresponsivities up to 261 A W^?1 (with a fast rising time of 20 ms and a falling time of 16 ms) in air and 722 A W^?1 in vacuum, respectively. Furthermore, the effects of back‐gate voltage and air adsorbates on the optoelectronic properties of the SnS₂ nanosheet have been systematically investigated. In addition, a high‐performance flexible photodetector based on SnS₂ nanosheet is also fabricated with a high responsivity of 34.6 A W^?1.     

High-photosensitivity polymer thin-film transistors based on poly（3-hexylthiophene）

Polymer thin-film transistors(PTFTs) based on poly(3-hexylthiophene) are fabricated by the spin-coating process,and their photo-sensing characteristics are investigated under steady-state visible-light illumination.The photosensitivity of the device is strongly modulated by gate voltage under various illuminations.When the device is in the subthreshold operating mode,a significant increase in its drain current is observed with a maximum photosensitivity of 1.7×10 3 at an illumination intensity of 1200 lx,and even with a relatively high photosensitivity of 611 at a low illumination intensity of 100 lx.However,when the device is in the on-state operating mode,the photosensitivity is very low:only 1.88 at an illumination intensity of 1200 lx for a gate voltage of-20 V and a drain voltage of -20 V.The results indicate that the devices could be used as photo-detectors or sensors in the range of visible light.The modulation mechanism of the photosensitivity in the PTFT is discussed in detail.     

The understanding of the memory nature and mechanism of the Ta2O5-gate-dielectric-based organic phototransistor memory

The memory nature and mechanism of the Ta₂O₅-gate-dielectric-based organic phototransistor memory (OPTM) have been studied. The UV–Vis absorption spectra and the X-ray photoelectron spectroscopy indicate that Ta₂O₅ owns positive interfacial charge because of the existence of Ta–OH. The hydroxide results in oxygen deficiency in Ta₂O₅ which is proposed to trap electrons. The characteristics of Ta₂O₅-based capacitor and the energy level alignment at Ta₂O₅–pentacene interface reveal that the electron-injection process is favorable which stimulates the electron-trapping process in Ta₂O₅. The Kelvin probe force microscopy of the Ta₂O₅-pentacene interface certificates the electron-injection and electron-trapping processes as well. It is the positive charges in Ta₂O₅ and energy level alignment that lead to the memory effect of Ta₂O₅-gate-dielectric-based OPTM. Compared to Ta₂O₅, polymethyl methacrylate (PMMA) does not have so strong a positive interface. Accordingly, PMMA films of different thickness are adopted on Ta₂O₅ to tune the Ta₂O₅-pentacene interface, offering control of the memory properties including the memory window and retention time. The understanding of the mechanism is at the forefront of devising high-performance OPTM devices.     

High-sensitive phototransistor based on vertical HfSe2/MoS2 heterostructure with broad-spectral response

Van der Waals heterostructures based on the two-dimensional (2D) semiconductor materials have attracted increasing attention due to their attractive properties. In this work, we demonstrate a high-sensitive back-gated phototransistor based on the vertical HfSe₂/MoS₂ heterostructure with a broad-spectral response from near-ultraviolet to near-infrared and an efficient gate tunability for photoresponse. Under bias, the phototransistor exhibits high responsivity of up to 1.42×10³ A/W, and ultrahigh specific detectivity of up to 1.39×10¹⁵ cm·Hz^1/2·W^-1. Moreover, it can also operate under zero bias with remarkable responsivity of 10.2 A/W, relatively high specific detectivity of 1.43×10¹⁴ cm·Hz^1/2·W^-1, ultralow dark current of 1.22 fA, and high on/off ratio of above 10⁵. These results should be attributed to the fact that the vertical HfSe₂/MoS₂ heterostructure not only improves the broadband photoresponse of the phototransistor but also greatly enhances its sensitivity. Therefore, the heterostructure provides a promising candidate for next generation high performance phototransistors.     

Highly sensitive near infrared organic phototransistors based on conjugated polymer nanowire networks

Highly sensitive near-infrared (NIR) organic phototransistors (OPTs) were fabricated using nanowire network based on a narrow bandgap donor-acceptor (D-A) polymer as the photoactive channel. The D-A polymer nanowire network-based NIR-OPTs exhibit high responsivity of ∼246 A/W under an NIR illumination source (850 nm) with a light intensity of ∼0.1 mW/cm². This value is over one order of magnitude higher than that of the structurally identical planar D-A polymer thin film OPTs. The high performance of the nanowire network-based phototransistors is attributed to the excellent hole transport ability, reduced density of the structural defects in the polymer nanowires, and improved contact at the channel layer/electrode interfaces. The high sensitivity and low cost solution-fabrication process render this OPT technology appealing and practically viable for application in large area NIR sensors.     

Quantum Dot–Carbon Nanotube Hybrid Phototransistor with an Enhanced Optical Stark Effect

Enhanced carrier–carrier interactions in hybrid nanostructures exhibit exceptional electronic and optoelectronic properties. Carbon nanotubes demonstrate excellent switching behavior with high on/off ratio and high mobility but do not show photoresponse in the visible range, whereas quantum dots (QDs) shows excellent optical response in various optical ranges which can be tuned with diameter. Here, a simple and effective way to develop hybrid phototransistors with extraordinary optoelectronic properties is presented by decorating semiconducting QDs on the surface of a single‐walled carbon nanotube (SWCNT). This hybrid structure demonstrates clear negative photoresponse and optical switching behavior, which could be further tuned by applying external gate bias in the future. A clear type conversion of SWCNT transistor from p‐type to n‐type caused by a charge transfer from attached QDs to CNT is demonstrated. Moreover, this hybrid structure also demonstrates an enhancement in ‘optical Stark effect’ without applying any external electric field. Charged SWCNT surface plays a key role behind the enhancement of optical Stark effect in QDs. The carrier dynamics of the QD and CNT heterostructures system highlights the potential application opportunity of the quantum dot systems, which can be adaptable to the current technologies.