Development Of High-performance Electronic Devices Research Articles

Schottky-barrier-free contacts with Janus WSSe 2D semiconductor using surface-engineered MXenes

Forming low-barrier contacts at metal/semiconductor interfaces is an important research area. The Fermi level pinning (FLP) effect is induced by strong interactions between 3D metal/semiconductor interfaces. By using a 2D metal in contact with a 2D semiconductor, the FLP effect can be weakened considerably, resulting in a reduction of the Schottky barrier height (SBH). Surface-engineered MXenes are the best electrode materials available presently. Therefore, herein, the interfacial properties of surface-engineered MXenes (M2CT2) (M=Hf, Mo, Ta, Zr, Nb; T = F, OH, O)/Janus WSSe (WSSe) heterostructures are systematically investigated using first-principles calculations. OH-terminated MXenes [M2C(OH)2]/WSSe heterostructures are found to form n-type ohmic contacts, and the tunnelling probabilities are high. O-terminated MXenes (M2CO2)/WSSe heterostructures tend to form p-type ohmic contacts and p-type Schottky contacts with a very low SBH, and the tunnelling probability is low. Conversely, F-terminated MXenes (M2CF2)/WSSe heterostructures form n-type and p-type Schottky contacts readily and n-type ohmic contacts (Hf2CF2/WSSe and Zr2CF2/SWSe heterostructures) partially, and the tunnelling probability is found to be low. In addition, the synergistic action of interface and intrinsic dipoles can effectively tune the contact type and SBH of the M2CT2/WSSe heterostructures, transforming the Mo2CF2/WSSe and Nb2CF2/WSSe heterostructures from n-type to p-type Schottky contacts. Through this novel strategy, an SB-free contact can be readily obtained, especially for OH-terminated MXenes (which are the most ideal electrode materials), followed by O-terminated MXenes. This work provides an important reference for the selection of suitable electrode materials and a novel approach for the development of high-performance electronic devices based on Janus WSSe.

All van der Waals Semiconducting PtSe2 Field Effect Transistors with Low Contact Resistance Graphite Electrodes.

Contact resistance is a multifaceted challenge faced by the 2D materials community. Large Schottky barrier heights and gap-state pinning are active obstacles that require an integrated approach to achieve the development of high-performance electronic devices based on 2D materials. In this work, we present semiconducting PtSe2 field effect transistors with all-van-der-Waals electrode and dielectric interfaces. We use graphite contacts, which enable high ION/IOFF ratios up to 109 with currents above 100 μA μm-1 and mobilities of 50 cm2 V-1 s-1 at room temperature and over 400 cm2 V-1 s-1 at 10 K. The devices exhibit high stability with a maximum hysteresis width below 36 mV nm-1. The contact resistance at the graphite-PtSe2 interface is found to be below 700 Ω μm. Our results present PtSe2 as a promising candidate for the realization of high-performance 2D circuits built solely with 2D materials.

Improved Bending Strength and Thermal Conductivity of Diamond/Al Composites with Ti Coating Fabricated by Liquid-Solid Separation Method.

In response to the rapid development of high-performance electronic devices, diamond/Al composites with high thermal conductivity (TC) have been considered as the latest generation of thermal management materials. This study involved the fabrication of diamond/Al composites reinforced with Ti-coated diamond particles using a liquid-solid separation (LSS) method. The interfacial characteristics of composites both without and with Ti coatings were evaluated using SEM, XRD, and EMPA. The results show that the LSS technology can fabricate diamond/Al composites without Al4C3, hence guaranteeing excellent mechanical and thermophysical properties. The higher TC of the diamond/Al composite with a Ti coating was attributed to the favorable metallurgical bonding interface compounds. Due to the non-wettability between diamond and Al, the TC of uncoated diamond particle-reinforced composites was only 149 W/m·K. The TC of Ti-coated composites increased by 85.9% to 277 W/m·K. A simultaneous comparison and analysis were performed on the features of composites reinforced by Ti and Cr coatings. The results suggest that the application of the Ti coating increases the bending strength of the composite, while the Cr coating enhances the TC of the composite. We calculate the theoretical TC of the diamond/Al composite by using the differential effective medium (DEM) and Maxwell prediction model and analyze the effect of Ti coating on the TC of the composite.

Future prospects of MXenes: synthesis, functionalization, properties, and application in field effect transistors.

MXenes are a family of two-dimensional (2D) materials that have drawn a lot of interest recently because of their distinctive characteristics and possible uses in a variety of industries. This review emphasizes the bright future prospects of MXene materials in the realm of FETs. Their remarkable properties, coupled with their tunability and compatibility, position MXenes as promising candidates for the development of high-performance electronic devices. As research in this field continues to evolve, the potential of MXenes to drive innovation in electronics becomes increasingly evident, fostering excitement for their role in shaping the future of electronic technology. This paper presents a comprehensive overview of MXene materials, focusing on their synthesis methods, functionalization strategies, intrinsic properties, and their promising application in Field Effect Transistors (FETs).

Electrical contact properties of 2D metal-semiconductor heterojunctions composed of different phases of NbS<sub>2</sub> and GeS<sub>2</sub>

Metal-semiconductor heterojunction (MSJ) is the basis for developing novel devices. Here, we consider different two-dimensional van der Waals MSJs consisting of different-phase metals H- and T-NbS<sub>2</sub> and semiconductor GeS<sub>2</sub>, and conduct an in-depth study of their structural stabilities, electronic and electrical contact properties, with an emphasis on exploring the dependence of the electrical contact properties of the MSJs on the different phases of metals. Calculation results of their binding energy, phonon spectra, AIMD simulations, and mechanical properties show that both heterojunctions are highly stable, which implies that it is possible to prepare them experimentally and feasible to use them for designing electronic devices. The intrinsic H-NbS<sub>2</sub>/GeS<sub>2</sub> and T-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunctions form p-type Schottky contacts and quasi-n-type Ohmic contacts, respectively. It is also found that their Schottky barrier heights (SBHs) and electrical contact types can be effectively modulated by an applied electric field and biaxial strain. For example, for the H-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, Ohmic contact can be achieved regardless of applying a positive/negative electric field or planar biaxial compression, while for the T-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, Ohmic contact can be achieved only at a very low negative electric field. The planar biaxial stretching can achieve quasi-Ohmic contact. In other words, when the semiconductor GeS<sub>2</sub> monolayer is used as the channel material of the field effect transistor and contacts different metal NbS<sub>2</sub> monolayers to form the MSJ, the interfacial Schottky barriers are distinctly different, and each of them has its own advantages in different situations (intrinsic or physically regulated). Therefore, this study is of great significance for understanding the physical mechanism of the electrical contact behaviors for H(T)-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, especially for providing the theoretical reference for selecting suitable metal electrodes for the development of high-performance electronic devices.

Exploring the phase behavior of C8-BTBT-C8 at ambient and high temperatures: insights and challenges from molecular dynamics simulations.

C8-BTBT-C8 is one promising candidate for the development of high-performance electronic devices based on thin-film technologies. Its monoclinic polymorph has a well-established role in thin-film growth. Yet, quite little information is available about its dynamics on the molecular scale, and the structures of the mesophases which form at high temperature (about 100 K above ambient temperature). The present study is devoted to the analysis of such phases, with the ultimate goal of developing molecular models. Already at ambient temperature, our molecular dynamics simulations reveal a rich conformational behavior of the alkyl side chains, with gauche conformations as leading structural defects. Heating promotes the formation of a stacking faulted mesophase (380 K), and a smectic phase, at 385 K, upon side chain melting. Although more disordered, this phase bears several analogies with the smectic A phase, experimentally observed at 382.5 K. At higher temperatures, the increase in configurational disorder is brought by molecular diffusion and other phenomena, finally leading to an isotropic molten phase. Our in-depth analysis, complemented by hot-stage polarizing microscopy data, provides interesting insights into this material, highlighting the challenges associated with the modeling of soft semiconducting systems.

First-principles investigations of structural and electronic properties of SnAs/SnAsCl heterostructure

In this work, we investigate the tunable structural and electronic properties of SnAs monolayer through chlorinated functionalization and the SnAs/SnAsCl heterostructure construction. Through chlorinated functionalization, we observe a remarkable transformation of the SnAs monolayer into a semiconducting SnAsCl monolayer with a direct band gap of 1.32 eV. This demonstrates the potential for controlling and tuning the electronic properties of SnAs through surface functionalization. Moreover, depending on the specific stacking patterns in the SnAs/SnAsCl heterostructure, we observe the formation of either Ohmic contact or Schottky contact. Particularly noteworthy is the presence of ultra-low Schottky barriers, measured at 0.03 eV, charge transport efficiency and improving device performance. The SnAs/SnAsCl heterostructure exhibits small tunneling probability, indicating a relatively low electron transparency. These findings pave the way for the development of high-performance electronic devices utilizing these heterostructures and offer promising opportunities for future technological advancements.

Thermal performance of an ultra-thin flat heat pipe with striped super-hydrophilic wick structure

• The UTFHP with striped super-hydrophilic wick structure was developed. • The mesh number of N = 200 and passage width of P = 1.5 mm is the best wick structure. • The UTFHP could tolerate 8 W heating load with the minimum thermal resistance of 0.26 K/W. The development of high-performance electronic devices requires high heat transfer components with small thickness and high thermal performance. This paper presented an ultra-thin flat heat pipe (UTFHP), and the total thickness and inner height is respectively 0.68 mm and 0.48 mm. The striped-channel structure was developed to withdraw the deformation of UTFHP and reduce the flow resistance. In order to improve the capillary performance of mesh wick, the oxidation treatment was finished by the thermal oxidation method. The thermal performance of UTFHPs was investigated under natural convection cooling condition. The effects of mesh structure, passage width and filling ratio on the thermal resistance and temperature distribution were analyzed. It is found that the UTFHP with mesh number of N = 200 and passage width P = 1.5 mm showed the best thermal performance under the filling ratio of φ = 57%. The minimum thermal resistance was 0.26 K/W with a maximum temperature of 74.07 °C at 8 W heating load, indicating that the proposed UTFHP was able to be a reliable candidate for the thermal management of electronic devices with high heat transfer rates.

Wide Band Gap P3S Monolayer with Anisotropic and Ultrahigh Carrier Mobility.

Phosphorene has offered an additional advantage for developing new optoelectronic devices due to its anisotropic and high carrier mobility. However, its instability in air causes a rapid degradation of the performance of the device. Thus, improving the stability of phosphorene while maintaining its original properties has become the key to the development of high-performance electronic devices. Herein, we propose that the formation of two-dimensional (2D) P-rich P-S compounds could achieve this goal. First-principles swarm-structural searches revealed two previously unkonwn P3S and P2S monolayers. The P3S monolayer, consisting of n-bicyclo-P6 units along the armchair direction, exhibits anisotropic and wide band gap characteristics. Interestingly, its carrier mobility reaches 1.11 × 104 cm2 V-1 s-1 and is much higher than in phosphorene. Its electronic band gap and optical absorption coefficients in the ultraviolet region reach 2.71 eV and 105 cm-1, respectively. Additionally, the P3S monolayer has a high structural stability and resistance to air oxidation.

Spontaneous Adsorption of Graphene Oxide on Multiple Polymeric Surfaces

The controllable integration of low-dimensional nanomaterials on solid surfaces is pivotal for the fabrication of next-generation miniaturized electronic and optoelectronic devices. For instance, organization of two-dimensional (2D) nanomaterials on polymeric surfaces paves the way for the development of flexible electronics for applications in wearable devices. Nevertheless, the understanding of the molecular interactions between these nanomaterials and the polymeric surfaces remains limited, which impedes the rational design of 2D nanomaterial-based functional coatings. In the current work, we report that graphene oxide (GO) nanosheets, in their dispersion phase, can be adsorbed on multiple polymeric surfaces in a spontaneous manner. Both experimental findings and simulational results indicate that the main driving force is hydrogen bonding interactions, although other molecular interactions such as polarity and dispersion ones contribute to the adsorption as well. The relatively high hydrogen bonding interactions cause not only increased GO surface coverage but also enhanced GO adsorption kinetics on polymeric surfaces. The adsorbed GO layers are robust, which can be explained by the large aspect ratios of GO nanosheets and the presence of multiple spots for molecular interactions. As a proof of concept, GO-covered polymethyl methacrylate effectively decreases surface static charges when compared with its pristine counterpart. The integration of the GO constituents turns many inert polymeric substrates into multifunctional hybrids, and the functional groups on GO can be used further to bridge with additional functional materials for the development of high-performance electronic devices.

Performance assessment of thermoelectric self-cooling systems for electronic devices

Due to the development of high-performance electronic devices, there exists a continuous need for effective and efficient cooling systems capable of removing large amounts of heat. A thermoelectric self-cooling system with forced air cooling based on a finned plate heat sink (case-a) and a water cooling based on a microchannel heat sink (case-b) is evaluated through a thermodynamic model. This article investigates the effect of the thermoelement geometry concerning its length and cross-section on the cooling capability of a self-cooling system for a wide range of heat fluxes (10 W to 200 W). Also, the effect of the efficiency related to the DC/DC converter between the thermoelectric generator and pumping devices is included in the analyses. The results show that shorter thermoelements with bigger cross-sections contribute to lower global thermal resistance and lower overheating of the electronic device. However, through the aspect ratio of the thermoelements (δ = cross-section/length), a practical limit was found defining how much shorter the thermoelement must be to satisfy a temperature constraint through the self-cooling condition for different fill factors, which corresponds to δ≤20. Beyond this limit, the performance of the self-cooling system is affected by the low conversion of heat into electricity used to run the pumping devices. The results also demonstrate for δ = 20 and fill factor equal to 0.95, that the temperature constraint (373 K) is satisfied for a heat flux equal to 124 W (case-a) and 173 W (case-b) when the efficiency of the DC/DC converter is 10%. Instead, a DC/DC converter with the highest efficiency (95%) rises the heat flux to 161 W (case-a) and 200 W (case-b), satisfying the constraint. Finally, this article summarizes the maximum heat flux for different thermoelements aspect ratios (δ ≤ 20) and fill factors where the self-cooling system for both cases satisfies a temperature constraint.

Influence of Thermal Annealing on the PdAl/Au Metal Stack Ohmic Contacts to p-AlGaN

In this study, a PdAl (20 nm)/Au (30 nm) metal stack scheme is used for forming low-ohmic-resistance contact on Mg-doped (1.5 × 1017 cm−3) p-type AlGaN at various annealing temperatures. Using a circular-transmission line model, the specific contact resistance (ρc) of PdAl/Au/p-AlGaN ohmic contact is determined via the current–voltage (I–V) characteristics. As-deposited contacts demonstrate non-linear behavior. However, the contact exhibits linear I–V characteristics with excellent ohmic contact of ρc = 1.74 × 10−4Ωcm2, when annealed at 600 °C for 1 min in a N2 atmosphere. The Ga and Al vacancies created at the PdAl/Au and p-AlGaN interfaces, which act as acceptors to increase the hole concentration at the interface. The out-diffusion of Ga as well as in-diffusion of Pd and Au to form interfacial chemical reactions at the interface is observed by X-ray photoelectron spectroscopy (XPS) measurements. The phases of the Ga–Pd and Ga–Au phases are detected by X-ray diffraction (XRD) analysis. Morphological results show that the surface of the contact is reasonably smooth with the root-mean-square roughness of 2.89 nm despite annealing at 600 °C. Based on the above experimental considerations, PdAl/Au/p-AlGaN contact annealed at 600 °C is a suitable p-ohmic contact for the development of high-performance electronic devices.

Effect of Thermal Grease on Thermal Conductivity for Mild Steel and Stainless Steel by ASTM D5470

Thermal management is a critical issue for the development of high-performance electronic devices. In this paper, thermal conductivity values of mild steel and stainless steel(STS) are measured by light flash analysis(LFA) and dynamic thermal interface material(DynTIM) Tester. The shapes of samples for thermal property measurement are disc type with a diameter of 12.6 mm. For samples with different thickness, the thermal diffusivity and thermal conductivity are measured by LFA. For identical samples, the thermal resistance(Rth) and thermal conductivity are measured using a DynTIM Tester. The thermal conductivity of samples with different thicknesses, measured by LFA, show similar values in a range of 5 %. However, the thermal conductivity of samples measured by DynTIM Tester show widely scattered values according to the application of thermal grease. When we use the thermal grease to remove air gaps, the thermal conductivity of samples measured by DynTIM Tester is larger than that measured by LFA. But, when we did not use thermal grease, the thermal conductivity of samples measured by DynTIM Tester is smaller than that measured by LFA. For the DynTIM Tester results, we also find that the slope of the graph of thermal resistance vs. thickness is affected by the usage of thermal grease. From this, we are able to conclude that the wide scattering of thermal conductivity for samples measured with the DynTIM Tester is caused by the change of slope in the graph of thermal resistance-thickness.

Dirac fermions in blue-phosphorus

We propose that Dirac cones can be engineered in phosphorene with fourfold-coordinated phosphorus atoms. The key is to separate the energy levels of the in-plane (s, px, and py) and out-of-plane (pz) oribtals through the sp2 configuration, yielding respective σ- and π-character Dirac cones, and then quench the latter. As a proof-of-principle study, we create σ-character Dirac cones in hydrogenated and fluorinated phosphorene with a honeycomb lattice. The obtained Dirac cones are at K-points, slightly anisotropic, with Fermi velocities of 0.91 and 1.23 times that of graphene along the ΓK and KM direction, and maintain good linearity up to ∼2 eV for holes. A substantive advantage of a σ-character Dirac cone is its convenience in tuning the Dirac gap via in-plane strain. Our findings pave the way for development of high-performance electronic devices based on Dirac materials.