Dark Current Reduction and Performance Improvements in Graphene/Silicon Heterojunction Photodetectors Obtained Using a Non-Stoichiometric HfOx Thin Oxide Layer.

Graphene/silicon heterojunction photodetectors suffer from a high dark current due to the high surface states and low barrier height at the interface, which limits their application. In this study, we introduce an HfOx interfacial layer via magnetron sputtering to address this issue. With this new structure, the dark current is reduced by six times under a bias voltage of -2 V. Under 460 nm illumination, the responsivity is 0.228A/W, the detectivity is 1.15 × 1011 cmHz1/2W-1, and the noise equivalent power is 8.75 × 10-5 pW/Hz1/2, demonstrating an excellent weak light detection capability. Additionally, the oxygen vacancies in the HfOx interfacial layer provide a conductive channel for charge carriers, resulting in a 2.03-fold increase in photocurrent and an external quantum efficiency of 76.5%. The photodetector maintains good photoresponse ability at a low bias voltage. This work showcases the outstanding performance of HfOx films as interfacial layer materials and provides a new solution for high-performance photodetectors, as well as a new path to improve the photovoltaic conversion efficiency of solar cells.

Tunable electronic and optical properties of MoTe2/InSe heterostructure via external electric field and strain engineering.

Based on first-principles calculation under density functional theory, the geometry, electronic and optical properties of the MoTe2/InSe heterojunction have been investigated. The results reveal that the MoTe2/InSe heterojunction has a typical type-Ⅱ band alignment and exhibits an indirect bandgap of 0.99 eV. In addition, the Z-scheme electron transport mechanism is capable of efficiently separating photogenerated carriers. The bandgap of the heterostructure changes regularly under applied electric field and exhibits a significant Giant Stark effect. Under an applied electric field of 0.5 V Å-1, the band alignment of the heterojunction shifts from type-Ⅱ to type-I. The application of strain produced comparable changes in the heterojunction. More importantly, the transition from semiconductor to metal is completed in the heterostructure under the applied electric field and strain. Furthermore, the MoTe2/InSe heterojunction retains the optical properties of two monolayers and produces greater light absorption on this basis, especially for UV light. The above results offer a theoretical basis for the application of MoTe2/InSe heterostructure in the next generation of photodetectors.

Atomic Layer Deposition of Ultrathin La2O3/Al2O3 Nanolaminates on MoS2 with Ultraviolet Ozone Treatment.

Due to the chemically inert surface of MoS2, uniform deposition of ultrathin high-κ dielectric using atomic layer deposition (ALD) is difficult. However, this is crucial for the fabrication of field-effect transistors (FETs). In this work, the atomic layer deposition growth of sub-5 nm La2O3/Al2O3 nanolaminates on MoS2 using different oxidants (H2O and O3) was investigated. To improve the deposition, the effects of ultraviolet ozone treatment on MoS2 surface are also evaluated. It is found that the physical properties and electrical characteristics of La2O3/Al2O3 nanolaminates change greatly for different oxidants and treatment processes. These changes are found to be associated with the residual of metal carbide caused by the insufficient interface reactions. Ultraviolet ozone pretreatment can substantially improve the initial growth of sub-5 nm H2O-based or O3-based La2O3/Al2O3 nanolaminates, resulting in a reduction of residual metal carbide. All results indicate that O3-based La2O3/Al2O3 nanolaminates on MoS2 with ultraviolet ozone treatment yielded good electrical performance with low leakage current and no leakage dot, revealing a straightforward approach for realizing sub-5 nm uniform La2O3/Al2O3 nanolaminates on MoS2.

Electric field and uniaxial strain tunable electronic properties of the InSb/InSe heterostructure.

In this study, the InSb/InSe heterostructure is systematically examined in terms of its electronic properties through first-principles calculations. According to our findings, the InSb/InSe heterostructure is a kind of unique direct band gap semiconductor, which has inherent type-II band alignment, resulting in significant photogenerated electron-hole pair separation in space. When the external electric field is applied, the Stark effect is observed in the band gap. Interestingly, in the application of the -0.3 V Å-1 electric field, such a heterostructure is transformed into type-I from type-II. Simultaneously, the band gap is also effectively controlled by uniaxial strain. In particular, high carrier mobility is obtained at a compressive strain of 4% on the Y-axis. To sum up, based on the results in the present work, the InSb/InSe heterostructure can be potentially used in nanoelectronic and optoelectronic devices.

Type-II tunable SiC/InSe heterostructures under an electric field and biaxial strain.

In this study, first-principles calculations based on the density functional theory (DFT) are exploited to investigate the electronic capabilities of SiC/InSe heterostructures. According to our results, the SiC/InSe heterostructure possesses an inherent type-II band alignment, which displays a noticeable Stark effect on the band gap under a stable electric field. Besides, the heterostructure exhibits a low carrier effective mass and a narrower band gap when it is subject to tensile strain. More interestingly, the transition from an indirect to a direct band gap occurs when 8% of compressive strain is applied. Taken together, findings in this study indicate that the SiC/InSe heterostructure opens up a new avenue for its application in the fields of optoelectronics and microelectronics.

Band alignment control in a blue phosphorus/C2N van der Waals heterojunction using an electric field.

Well-controlled band engineering of a blue phosphorus/C2N van der Waals (vdW) heterojunction is investigated by density functional theory (DFT) calculations. The heterojunction has a natural type-II band alignment with a direct band gap value of 1.514 eV, which gives the enormous potential for solar cell applications. When the heterojunction is under solar illumination, the photogenerated electron-hole pairs can separate out on the disparate monolayers effectively. It induces the formation of spatially indirect excitons. Furthermore, it is found that the band gap of this heterojunction exhibits approximately linear variation with respect to the perpendicular external electric field. Very interestingly, a band alignment change from type-II to type-I occurs at an applied electric field of -0.2 V Å-1. This characteristic provides an attractive possibility to obtain novel multifunctional devices.

Tunable electronic properties of an Sb/InSe van der Waals heterostructure by electric field effects.

The electronic properties of an Sb/InSe heterostructure are investigated by using the density functional theory method. A type-II staggered-gap band alignment is achieved from the Sb/InSe vdW heterostructure with the Sb layer dominates the lowest energy holes as well as the lowest energy electrons are contributed by the InSe layer, which facilitates the spatial effective separation of photogenerated electron-hole pairs. Additionally, an indirect-direct band gap transition can be triggered via varying the interlayer distance. More fascinatingly, the characteristic of type-II band alignment is robust, while the band gap values are tunable with respect to a moderate external electric field, even leading to an intriguing semiconductor-metal transition at a strong electric field. These results are expected to provide meaningful guidelines for the design of novel nanoelectronic and optoelectronic devices based on the Sb/InSe heterostructure.

Erratum: Publisher's Note: "A particle manipulation method and its experimental study based on opposed jets" [Biomicrofluidics 12, 024110 (2018)].

[This corrects the article DOI: 10.1063/1.5020600.].

A particle manipulation method and its experimental study based on opposed jets.

A particle manipulation method was presented in this paper based on opposed jets. In such a method, particles were trapped near the stagnation point of the flow field and moved by controlling the position of the stagnation point. The hold direction of the flow to the particle was changed by changing the orientation of the opposed-jet flow field where a particle is trapped. Subsequently, the directional and quantitative movement of the particle in any direction was achieved. Taking micron particles as examples, we analyzed the control mechanism of particles based on opposed jets and evaluated the influence of jet velocity, inner diameter, distance of end face, radial error, and position of capillaries on the particle control performance by simulations. The feasibility of the proposed method was proved by a great number of experiments, and the results demonstrated that particles with the arbitrary size and shape can be trapped and moved directionally and quantitatively by constructing an opposed-jet flow field. The trapping and position control of particles can be manipulated without any contact with proper flow field parameters.

Fabrication of Self-Powered Fast-Response Ultraviolet Photodetectors Based on Graphene/ZnO:Al Nanorod-Array-Film Structure with Stable Schottky Barrier.

A Schottky UV photodetector based on graphene/ZnO:Al nanorod-array-film (AZNF) structure has been fabricated. Different from the previously reported graphene/ZnO photodetectors, this photodetector has a stable Schottky barrier which does not disappear under UV light. Thus, the UV photodetector can work as a high-performance self-powered device. The key to improve the stability of the Schottky barrier is a two-step surface treatment process. As a result, the self-powered photodetector exhibits a UV-to-visible rejection ratio of about 1 × 102, a responsivity of 0.039 A W1-, a short rise time of 37 µs, and a decay time of 330 µs. Furthermore, the photodetector is able to keep the responsivity under low light conditions. In comparison with the previously reported graphene/ZnO UV photodetectors, the photodetector exhibits a higher responsivity at zero bias and a faster response speed. This study provides a potential way to fabricate high-performance self-powered UV photodetectors.