The Ge-ZnSe heterojunction has been prepared by vacuum evaporation of the ZnSe onto single-crystal p-type germanium substrates.' The growth conditions have been studied in terms of epitaxial growth on different crystallographic orientations in degrees of vacuum down to the ultra-highvacuum region. Measurements have also been made of the electrical characteristics, capacitance properties, and photoelectric response of the diode. From these measurements a realistic band model has emerged involving intrinsic and extrinsic defects present in the bulk and interfacial region of the zinc selenide. The results of this investigation are compared with those from devices grown by vapour phase epitaxy283 and the data presented suggests that a Mott-type barrier4 rather than a Schottky barrier is present at the germanium-zinc-selenide interface. Techniques have been developed for the removal of this Mott barrier and the resulting change in the physical properties and band structure will be given. Possible applications of heterojunctions with this particular band structure will be discussed. 295, 1968. ', N.M. Schottky-barrier diodes of chromium on n-type epitaxial gallium arsenide phosphide (GaAsP) were studied from 25" to 440°C. The diodes showed significant rectification properties up to a temperature of 440°C. At high temperature the reverse leakage current was 1.15 milliamperes at 25 volts with a diode area of 1.14 X 10-3 cm2 as compared with 0.25 microampere at room temperature.The chromium was evaporated from a tungsten filament in a vac-ion system at a pressure of less than 10-8 Torr. Silver was alloyed into the GaAs substrate to provide a good ohmic contact over the entire temperature range. The epitaxial layer was 200 Hm thick.The slope of the In current versus voltage curves was l.lkT/q. The barrier height for the chromium contact was 1.15 eV from the capacitancevoltage measurements and 1.05 eV from the current-voltage measurements.From the plot of ln(JJT2) versus 1/T, where J, is current density and T is temperature, the effective Richardson constant for these diodes is approximately 2.5 A/crnz/'KZ. The calculated value of carrier concentration from the capacitance-voltage curves was 8 X 1015/cm3. The reversebreakdown voltage of the diodes was in excess of BO volts a t room temperature. 146
The applications of any two-dimensional (2D) semiconductor devices cannot bypass the control of metal-semiconductor interfaces, which can be severely affected by complex Fermi pinning effects and defect states. Here, we report a near-ideal rectifier in the all-2D Schottky junctions composed of the 2D metal 1 T′-MoTe2 and the semiconducting monolayer MoS2. We show that the van der Waals integration of the two 2D materials can efficiently address the severe Fermi pinning effect generated by conventional metals, leading to increased Schottky barrier height. Furthermore, by healing original atom-vacancies and reducing the intrinsic defect doping in MoS2, the Schottky barrier width can be effectively enlarged by 59%. The 1 T′-MoTe2/healed-MoS2 rectifier exhibits a near-unity ideality factor of ~1.6, a rectifying ratio of >5 × 105, and high external quantum efficiency exceeding 20%. Finally, we generalize the barrier optimization strategy to other Schottky junctions, defining an alternative solution to enhance the performance of 2D-material-based electronic devices.
Monolayer 2D semiconductors (e.g., MoS2) are of considerable interest for atomically thin transistors but generally limited by insufficient carrier mobility or driving current. Minimizing the lattice defects in 2D semiconductors represents a common strategy to improve their electronic properties, but has met with limited success to date. Herein, a hidden benefit of the atomic vacancies in monolayer 2D semiconductors to push their performance limit is reported. By purposely tailoring the sulfur vacancies (SVs) to an optimum density of 4.7% in monolayer MoS2, an unusual mobility enhancement is obtained and a record‐high carrier mobility (>115 cm2 V−1 s−1) is achieved, realizing monolayer MoS2 transistors with an exceptional current density (>0.60 mA µm−1) and a record‐high on/off ratio >1010, and enabling a logic inverter with an ultrahigh voltage gain >100. The systematic transport studies reveal that the counterintuitive vacancy‐enhanced transport originates from a nearest‐neighbor hopping conduction model, in which an optimum SV density is essential for maximizing the charge hopping probability. Lastly, the vacancy benefit into other monolayer 2D semiconductors is further generalized; thus, a general strategy for tailoring the charge transport properties of monolayer materials is defined.
Solution self-assembly of coil-crystalline diblock copolypeptoids has attracted increasing attention due to its capability to form hierarchical nanostructures with tailorable morphologies and functionalities. While the N-substituent (or side chain) structures are known to affect the crystallization of polypeptoids, their roles in dictating the hierarchical solution self-assembly of diblock copolypeptoids are not fully understood. Herein, we designed and synthesized two types of diblock copolypeptoids, i.e., poly( N -methylglycine)- b -poly( N -octylglycine) (PNMG- b -PNOG) and poly( N -methylglycine)- b -poly( N -2-ethyl-1-hexylglycine) (PNMG- b -PNEHG), to investigate the influence of N-substituent structure on the crystalline packing and hierarchical self-assembly of diblock copolypeptoids in methanol. With a linear aliphatic N-substituent, the PNOG blocks pack into a highly ordered crystalline structure with a board-like molecular geometry, resulting in the self-assembly of PNMG- b -PNOG molecules into a hierarchical microflower morphology composed of radially arranged nanoribbon subunits. By contrast, the PNEHG blocks bearing bulky branched aliphatic N-substituents are rod-like and prefer to stack into a columnar hexagonal liquid crystalline mesophase, which drives PNMG- b -PNEHG molecules to self-assemble into symmetrical hexagonal nanosheets in solution. A combination of time-dependent small/wide-angle X-ray scattering and microscopic imaging analysis further revealed the self-assembly mechanisms for the formation of these microflowers and hexagonal nanosheets. These results highlight the significant impact of the N-substituent architecture (i.e., linear versus branched) on the supramolecular self-assembly of diblock copolypeptoids in solution, which can serve as an effective strategy to tune the geometry and hierarchical structure of polypeptoid-based nanomaterials.
Flexible optoelectronics, as promising components hold shape‐adaptive features and dynamic strain response under strain engineering for various intelligent applications. 2D materials with atomically thin layers are ideal for flexible optoelectronics because of their high flexibility and strain sensitivity. However, how the strain affects the performance of 2D materials‐based flexible optoelectronics is confused due to their hypersensitive features to external strain changes. It is necessary to establish an evaluation system to comprehend the influence of the external strain on the intrinsic properties of 2D materials and the photoresponse performance of their flexible optoelectronics. Here, a focused review of strain engineering in 2D materials‐based flexible optoelectronics is provided. The first attention is on the mechanical properties and the strain‐engineered electronic properties of 2D semiconductors. An evaluation system with relatively comprehensive parameters in functionality and service capability is summarized to develop 2D materials‐based flexible optoelectronics in practical application. Based on the parameters, some strategies to improve the functionality and service capability are proposed. Finally, combining with strain engineering in future intelligence devices, the challenges and future perspective developing 2D materials‐based flexible optoelectronics are expounded.
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