The unique property of bilayer graphene to show a band gap tunable by external electrical fields enables a variety of different device concepts with novel functionalities for electronic, optoelectronic and sensor applications. So far the operation of bilayer graphene based field effect transistors requires two individual gates to vary the channel's conductance and to create a band gap. In this paper we report on a method to increase the on/off ratio in single gated bilayer graphene field effect transistors by adsorbate doping. The adsorbate dopants on the upper side of the graphene establish a displacement field perpendicular to the graphene surface breaking the inversion symmetry of the two graphene layers. Low temperature measurements indicate, that the increased on/off ratio is caused by the opening of a mobility gap. Beside field effect transistors the presented approach can also be employed for other bilayer graphene based devices like photodetectors for THz to infrared radiation, chemical sensors and in more sophisticated structures such as antidot- or superlattices where an artificial potential landscape has to be created.
The properties of semiconductors can be crucially impacted by midgap states induced by dopants, which can be native or intentionally incorporated in the crystal lattice. For Bernal-stacked bilayer graphene (BLG), which has a tunable bandgap, the existence of midgap states induced by dopants has been conjectured, but never confirmed experimentally. Here, we report scanning tunneling microscopy and spectroscopy results, supported by tight-binding calculations, that demonstrate the existence of midgap states in BLG. We show that the midgap state in BLG -- for which we demonstrate gate-tunability …
Impact of dopant species on the interfacial trap density and mobility in amorphous In-X-Zn-O solution-processed thin-film transistors
In/Zn氧化物与各种X原子的合金化稳定了IXZO结构，但在化合物中产生电子陷阱，降低了电子迁移率。为了评估后者是否与X元素的氧亲和力或离子半径有关，通过溶胶-凝胶过程合成了几个IXZO样品，其中含有大量（14）X元素。IXZO通过XPS、SIMS、DRX和UV光谱表征，并用于制造薄膜晶体管。从TFT电学特性和低频噪声中提取的沟道迁移率和界面缺陷密度NST呈增加趋势，迁移率和NST的值呈指数关系。在In-Ga-Zn-O中获得了最高的迁移率（8.5 cm 2/Vs），并且对于Sb和Sn掺杂的IXZO获得了稍低的值，NST为约2 E12 cm 2/eV，接近于In-Zn-O参考TFT的NST。这是由于Ga、Sb和Sn的电负性高于Zn和In，它们的离子半径值接近In和Zn的离子半径值。因此，Ga，Sb和Sn在溶胶-凝胶过程中诱导的In-O和Zn-O序列的扰动较弱，而X元素具有较低的电负性和不同的离子半径。具有X = Ca、Al、Ni和Cu的TFT表现出最低的迁移率和NST > 1 E13 cm 2/eV，这很可能是由于金属或氧化物簇的形成。
The electronic structures of TiO2/Ti4O7, Ta2O5/TaO2 interfaces and the interfacial effects of dopants
利用屏蔽交换（sX-LDA）泛函研究了TiO 2/Ti4 O 7和Ta 2 O 5/TaO 2界面的电子结构。这两种双层结构都是用于高性能RRAM的有用基础结构。我们发现两个界面的系统费米能都在相应化学计量氧化物的导带边之上。根据Ta 2 O 5和TiO 2中氧空位的电荷跃迁能级，氧空位稳定在-2带电状态。我们建议引入界面掺杂剂使系统费米能级下移，从而使+2电荷氧空位能够稳定，这对于电场下的受控开关是重要的。提出了几种偶极模型来解释界面掺杂引起的费米能级移动。
High mobility and high on/off ratio field-effect transistors based on chemical vapor deposited single-crystal MoS2 grains
我们报告了场效应晶体管（FET）与单晶二硫化钼（MoS 2）的化学气相沉积（CVD）合成的通道。对于双层MoS 2 FET，迁移率为~17 cm ~ 2 V ~（-1）s ~（-1），开/关电流比为~108，这比基于CVD多晶MoS 2膜的FET高得多。通过避免由转移过程引入的晶界和污染的有害影响，直接沉积在SiO2上的CVD MoS 2原子层的质量与最佳剥离的MoS 2薄片相当。结果表明，CVD法是制备高质量MoS_2原子层的一种可行方法。
Organic Electrochemical Transistor Arrays with Integrated Lipid-Sealed Femtolitre Chambers for Simultaneous Electrical and Optical Detection of Membrane Protein Activity
University of New South Wales（新南威尔士大学）；The University of Tokyo（东京大学）
The past decade has seen rapid growth in the research area of graphene and its application to novel electronics. With Moore's law beginning to plateau, the need for post-silicon technology in industry is becoming more apparent. Moreover, existing technology is insufficient for implementing terahertz detectors and receivers, which are required for a number of applications including medical imaging and security scanning. Graphene is considered to be a key potential candidate for replacing silicon in existing CMOS technology as well as realizing field effect transistors for terahertz detection, d…
Explosive crystallization (EC) is often observed when using nanosecond-pulsed melt laser annealing (MLA) in amorphous silicon (Si) and germanium (Ge). The solidification velocity in EC is so fast that a diffusion-less crystallization can be expected. In the contacts of advanced transistors, the active level at the metal/semiconductor Schottky interface must be very high to achieve a sub-10^{-9} ohm.cm2 contact resistivity, which has been already demonstrated by using the dopant surface segregation induced by MLA. However, the beneficial layer of a few nanometers at the surface may be easily co…
Valley-Landscape Engineering in Bilayer WSe$_2$ Gate-All-Around Transistors
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)（物质·材料纳米构筑研究中心，日本国立材料研究所）；Kwansei Gakuin University（关西学院大学）
Porous graphene structures, also termed graphene nanomeshes (GNMs), are garnering increasing interest due to their potential application to important technologies such as chemical sensing, ion-filtration, and nanoelectronics. Semiconducting GNMs designed to have fractional eV band gaps are good candidates for graphene-based electronics, provided that a mechanism for their stable and controlled doping is developed. Recent work has shown that controlled passivation of the edges of subnanometer pores and subsequent doping by atoms or molecules gives rise to {\it p}- and {\it n}-doped GNM structur…
Layer-by-layer growth of highly aligned MoS$_2$ nanoribbon arrays
Kyushu University（九州大学）；The University of Osaka（大阪大学）；University of Tsukuba（筑波大学）；Pohang University of Science and Technology (POSTECH)（浦项科技大学）；Kumamoto University（熊本大学）；National Institute of Advanced Industrial Science and Technology (AIST)（国立产业技术综合研究所）
Cr resonant impurity for studies of band inversion and band offsets in IV-VI semiconductors
Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所）；Center for Science and Innovation in Spintronics, Tohoku University（东北大学自旋电子学科学与创新中心）；Research Institute of Electrical Communication, Tohoku University（东北大学电气通信研究所）；International Research Centre MagTop, Institute of Physics Polish Academy of Sciences（波兰科学院物理研究所磁顶国际研究中心）；ENSEMBLE3 Centre of Excellence for Nanophotonics, Advanced Materials and Novel Crystal growth-based Technologies（纳米光子学、先进材料及新型晶体生长技术卓越中心 ENSEMBLE3）；Faculty of Physics, University of Warsaw（华沙大学物理学院）
Investigation of nitrogen polar p-type doped GaN/AlxGa(1-x)N superlattices for applications in wide-bandgap p-type field effect transistors
本论文研究了N极性调制掺杂p-AlGaN/GAN超晶格的MOCVD生长及其电学性质。空穴层电荷密度和迁移率作为SL中的p型掺杂剂Mg的浓度和SL周期数的函数进行了研究。进行室温霍尔测量以确定空穴迁移率和薄层电荷密度。当空穴密度随着SL周期数的增加而增加时，空穴迁移率基本上不受影响，对于Mg调制掺杂为7.5e18 cm-3的N极性SL，在同时具有6.5e13 cm-2的高空穴密度时，空穴迁移率高达18 cm 2/Vs。对于可比较的均匀掺杂的Ga极性SL样品，测量到11 cm 2/Vs的迁移率。还报道了GAN/AlGaN材料系统的最低薄层电阻为5 kOhm/sq。测试结构的晶体管也被制造来研究这些SL结构的适用性，其中平面器件导致5 mA/mm的电流，并且FinFET结构导致超过100 mA/mm的电流。
Low-energy electron-irradiation effect on transport properties of graphene field effect transistor
我们研究了低能量电子束照射到10 keV的石墨烯基场效应晶体管的影响。我们制造金属双层电极以接触$_2$上的单层和双层石墨烯薄片，获得比接触电阻率$ρ_c \simeq 19 kΩμm^2$和高达4000 cm $^2$ V $^{-1}$ s $^{-1}$的载流子迁移率。通过使用高掺杂的p-Si/SiO $_2$衬底作为背栅，我们分析了器件的输运特性以及对压力和电子轰击的依赖性。我们表明，低能量照射是有害的晶体管电流能力，导致接触电阻的增加和载流子迁移率的减少，即使在电子剂量低至30 $e^-/nm^2$。我们还表明，经过几次重复的电气测量后，被照射的设备恢复到原始状态。
Penta-graphene (PG) is a carbon allotrope that has recently attracted the attention of the materials science community due to its interesting properties for renewable energy applications. Although unstable in its pure form, it has been shown that functionalization may stabilize its structure. A question that arises is whether its outstanding electronic properties could also be further improved using such a procedure. As PG bilayers present both sp$^2$ and sp$^3$ carbon planes, it consists of a flexible candidate for functionalization tuning of electromagnetic properties. In this work, we perfo…
When twisted to angles near 1°, graphene multilayers provide a new window on electron correlation physics by hosting gate-tuneable strongly-correlated states, including insulators, superconductors, and unusual magnets. Here we report the discovery of a new member of the family, density-wave states, in double bilayer graphene twisted to 2.37°. At this angle the moiré states retain much of their isolated bilayer character, allowing their bilayer projections to be separately controlled by gates. We use this property to generate an energetic overlap between narrow isolated electron and hole bands …
High-level first-principles computations predict blue phosphorene bilayer to be a two-dimensional metal. This structure has not been considered before and was identified by employing a block-diagram scheme that yields the complete set of five high-symmetry stacking configurations of buckled honeycomb layers, and allows their unambiguous classification. We show that all of these stacking configurations are stable or at least metastable configurations both for blue phosphorene and gray arsenene bilayers. For blue phosphorene, the most stable stacking configuration has not yet been reported, and …
