ACS Applied Electronic Materials最新文献

Germanium-based materials are essential for the integration of Group IV optoelectronics in silicon devices. In addition to tensile strain, high n-type doping is critical, as it provides abundant carriers for recombination, potentially enabling higher photoemissions from Ge-based materials. We report here record-high 68% doping activation on n-Ge with ≥10²⁰ cm^–3 carrier density. This study centers on Sb-doped n-type Ge-on-insulator thin films with Si or Sn alloying grown using high-speed continuous-wave laser annealing (CWLA). Crystal mapping revealed the growth of polycrystalline n-GeSn and n-GeSi thin films with grain sizes up to 4 μm in diameter. Micro-PL measurements showed the PL intensity of n-Ge to be enhanced by the alloying of Sn and Si, with peak intensity 1.5 and 3 times higher for n-GeSn and n-GeSi, respectively. Raman peak red shift and broadening are observed in the samples, indicating high tensile strain and n-type doping. The measured carrier density of CWLA-grown films aligns well with the PL intensity trend, suggesting the process has promise for achieving electrically improved Ge-based thin films.

Recently, amorphous Ga₂O₃-based photodetectors are garnering interest for their relative ease-of-growth at room temperature and their virtuous use in flexible electronics. However, a major concern that remains is the huge trade-off between key performance parameters, viz., photoresponse and response time. Being replete with oxygen vacancies, acting as trap centers, devices usually boast a large photoresponse but at the cost of longer response time due to prolonged carrier recombination. Most of remedial measures to offset this trade-off include oxygen vacancy engineering but in a continuous manner, implying creating/deleting vacancies throughout the film thickness, leading to a change in only one of the parameters. Herein, we propose defect engineering in amorphous Ga₂O₃ by grading oxygen vacancies using an intermittent oxygen supply. XPS depth profile studies confirm gradation of vacancies, which may be accessed by applying a different bias, in resonance with electric field distribution simulations. Graded vacancy films show negligible persistent photoconductivity, a high PDCR of 3 × 10³, a high UV–vis rejection ratio of 1.49 × 10⁴, and a fast fall time of 85 ms as opposed to continuous supply films, which show either high photoresponse or fast speed (in seconds). This work provides a way to use graded oxygen vacancies as tool in defect engineering to offset the trade-off and achieve high photoresponse and fast response time in amorphous Ga₂O₃ films simultaneously.

Two-dimensional (2D) intrinsic ferromagnetic (FM) materials play a crucial role in spintronics. Through a systematic research of the 2H-MoS₂ bilayer (BL) with self-intercalation (SI) of Mo atom, we have discovered that SI can introduce a long-range magnetic order, as Mo_SI atoms lose electrons. The MoS₂ BLs (Mo_mS_n) with self-intercalated Mo (Mo_SI) atoms show antiferromagnetic (AFM) order under a high concentration of Mo_SI atoms, where the direct exchange interaction dominates over the superexchange interaction. Mo_mS_n becomes half-metal (HM) with interlayer FM order after Mo’s self-intercalation, under lower Mo_SI atom concentrations, independent of the stacking orders. Mo₉S₁₆-AA exhibits HM with FM order, with a corresponding Curie temperature (T_c) of 35 K. Mo_mS_n-AA and AB stackings with a lower concentration of Mo_SI atoms transform into half semiconductors (HSCs). Moreover, the magnetic anisotropy energies (MAEs) of Mo₉S₁₆-AA and AB stackings are −0.080 and −1.06 meV/f.u., suggesting that the magnetic easy axis (EA) of Mo_mS_n tends to the [100] direction, regardless of the stacking orders. However, the MAEs of Mo_mS_n-AA and AB stackings differ due to variations in the hybridization interaction between Mo’s d orbitals. The formation energies of Mo_mS_n change with the chemical potential of S (μ_s) and the concentration of Mo_SI atoms. Furthermore, the formation energy (ε_f) monotonically increases as the concentration of Mo_SI monotonically increases. Additionally, Mo_mS_n with Mo_SI atoms could be synthesized under a higher chemical potential of Mo atom (μ_Mo). The Mo_mS_n-AB stackings are always more stable than the AA stackings. Self-intercalated Mo_mS_n exhibits good dynamic and thermal stability at 300 and 600 K, respectively. These findings suggest a promising approach to introducing a modulated long-range FM order and electromagnetic properties into 2H-MoS₂ and other transition metal dichalcogenides (TMDs).

Addressing contact resistance challenges at the interface between metals and transition-metal dichalcogenides (TMDs) remains a complex task due to the persistent Fermi level pinning (FLP) effect near the conduction band minima. Various methods have been explored to mitigate FLP by reducing the chemical interaction between metals and semiconductors. However, these approaches often lead to undesirable consequences, such as reduced adhesion and increased tunneling resistance, ultimately resulting in poor interface quality. A promising solution to overcome these limitations lies in the use of substitutionally doped semiconductor/metal interfaces. We conducted a thorough investigation using first-principles calculations, focusing on S-substituted WS₂-metal interfaces involving commonly used metals such as Ag, Au, Cu, Pd, Pt, Sc, and Ti. Additionally, we explored the incorporation of nonmetallic dopants, including C, Cl, N, F, O, and P, into the WS₂ surface. Our analysis revolved around several critical parameters, including adhesion strength, Schottky barrier height (SBH), tunnel barrier, charge transfer across the interface, and interface dipole formation. Our study demonstrated that substitutionally doped interfaces can undergo Fermi level depinning while maintaining an enhanced adhesion strength and lower tunneling barrier at the interface. This finding marks a departure from existing methods and offers a promising avenue for inducing p-type contact polarity and addressing contact resistance challenges in TMDs.

Flexible temperature sensors are becoming increasingly important these days. In this work, we explore graphene oxide (GO)/poly(vinyl alcohol) (PVA) nanocomposites for potential application in temperature sensors. The influence of the mixing ratio of both materials, the reduction temperature, and passivation on the sensing performance has been investigated. Various spectroscopic techniques revealed the composite structure and atomic composition. These were complemented by semiempirical quantum chemical calculations to investigate rGO and PVA interaction. Scanning electron and atomic force microscopy measurements were carried out to evaluate dispersion and coated film quality. The temperature sensitivity has been evaluated for several composite materials with different compositions in the range from 10 to 80 °C. The results show that a linear temperature behavior can be realized based on rGO/PVA composites with temperature coefficients of resistance (TCR) larger than 1.8% K^–1 and a fast response time of 0.3 s with minimal hysteresis. Furthermore, humidity influence has been investigated in the range from 10% to 80%, and a minor effect is shown. Therefore, we can conclude that rGO/PVA composites have a high potential for excellent passivation-free, humidity-independent, sensitive, and fast response temperature sensors for various applications. The GO reduction is tunable, and PVA improves the rGO/PVA sensor performance by increasing the tunneling effect and band gap energy, consequently improving temperature sensitivity. Additionally, PVA exhibits minimal water absorption, reducing the humidity sensitivity. rGO/PVA maintains its temperature sensitivity during and after several mechanical deformations.

This study presents a straightforward approach for fabricating heterogeneous complementary FET (CFET) devices. The process flow commences with a SiGe/Ge/Si epitaxial multilayer structure grown on a SOI substrate. The source/drains for both stacked devices were straightforwardly performed through P and B implantations with precise depth control, respectively. The isolation of the top p-SiGe FET from the bottom n-Si FET was achieved by etching away the middle Ge sacrificial layer and subsequently filled with SiO₂ dielectric material. The etching selectivity of Ge over Si and Si_0.8Ge_0.2 by utilizing a H₂O₂ solution was nearly infinite, resulting in a flawless structure with p-SiGe channels stacked over n-Si channels. Finally, a functional CFET inverter device composed of a top inversion mode (IM) SiGe nanosheet pFET and a bottom IM Si nanosheet nFET was demonstrated.

Amorphous materials have great potential application in gas sensors due to their abundant active sites. However, it is still a challenge to regulate their sensing performance. In this work, we developed a synthesis method of amorphous bimetallic cobalt-based transition-metal oxides, which were prepared via two steps, namely, coprecipitation of bimetallic hydroxides and then annealing at elevating temperature. Sn, Mg, and Zn as the second metal were introduced to prepare amorphous CoSn–O, CoMg–O, and CoZn–O. They were further used to fabricate gas sensors. A sensing investigation revealed that the sensors present different sensing behaviors, in which the CoSn–O, CoMg–O, and CoZn–O sensors show selectivity to TEA, EtOH, and n-BuNH₂, respectively. A sensor array based on these three types of sensors was constructed. The actual concentrations of the mixing gases of TEA, EtOH, and n-BuNH₂ can be obtained by matrix calculation with an error value of less than 10%. Finally, the sensing processes were discussed, and the sensing mechanism can be attributed to the surface resistance control model. This research affords a convenient method to synthesize amorphous bimetallic oxides with regulated properties for sensing application.

Reduced graphene oxide (RGO)-modified copper(I) oxide (Cu₂O–RGO) is a high-performance composite and a low-cost photocatalyst for methylene blue (MB) degradation. To evaluate the effect of RGO on the photocatalytic performances of Cu₂O–x% RGO composites (where x is the loading amount of RGO) in MB degradation, Cu₂O was separately loaded with 10, 20, and 30 wt % RGO via a precipitation method. We synthesized a Cu₂O–30% RGO composite with a superior surface area (S_BET) of 43.701 m²/g, which provided a large active area for MB photodegradation. Cu₂O–30% RGO composite was significantly more effective as a catalyst than bare Cu₂O for MB photodegradation, as it degraded 99.2% MB in only 30 min under visible-light irradiation without oxidation agents as compared to the case of bare Cu₂O (17.5% MB degradation). Notably, the Cu₂O–30% RGO composite afforded the largest rate constant of 0.10193 L/min under visible-light irradiation, which was twice that of the Cu₂O–30% RGO composite without irradiation (0.0561 L/min). Electron (e^–) capture efficacy of RGO in suppressing electron (e^–)–hole (h⁺) pairs recombination was demonstrated, and a plausible mechanism was proposed to rationalize the high photocatalytic efficiency of Cu₂O–30% RGO. The RGO in Cu₂O–RGO composites played crucial roles, narrowing the band gap, extending the lifetime, and substantially enhancing the photocatalytic activity of Cu₂O. Durability and reusability of the catalysts were also examined, and MB degradation by the Cu₂O–30% RGO composite was maintained at 95% in the second decolorization cycle followed by a decline to 87% in the fifth decolorization cycle, rendering the Cu₂O–30% RGO composite appropriate for use in real-time environmental applications. This study provides an effective photocatalyst for the degradation of organic pollutants in wastewater and suggests its potential for future applications in related fields. Furthermore, herein, the role of RGO as an electron capturer in Cu₂O–RGO composites for MB degradation under visible-light irradiation is comprehensively analyzed for the first time.

Thermoelectric (TE) generators, based on thermoelectric materials, can efficiently convert thermal energy into electricity via the Seebeck effect, showing great promise for waste-heat recovery research. Recent advancements in TE composites of conductive polymer/carbon nanotubes have been significant. This study evaluates the thermoelectric properties of organic TE films and generators by combining naphthalene diimide (NDI) polymers with single-walled carbon nanotubes (SWCNTs). The results reveal that P(NDI-HTO)/SWCNT composite films containing free radicals and alkyl side chains have enhanced thermoelectric properties compared to P(NDI-HT)/SWCNT composite films without free radicals and P(NDI-TP)/SWCNT composite films containing polar side chains. Among them, maximum power factors reach 264.1 ± 21.9 μW m^–1 K^–2 for p-type and 72.2 ± 1.5 μW m^–1 K^–2 for n-type composite films, marking increases of 113% and 32%, respectively, over pristine SWCNT films. Furthermore, a flexible thermoelectric generator based on P(NDI-HTO)/SWCNT, with five pairs of p–n junctions, achieves an output voltage of 28.8 mV and an output power of 1.2 μW at a 60 K temperature differential. These improvements in thermoelectric properties are primarily due to the effective modulation of molecular energy levels, enhancing the charge transfer process between NDI polymers and SWCNTs.

This review presents a comparative analysis of the analog switching performance of oxide- and two-dimensional (2D)-material-based memristors, focusing on their application in neuromorphic computing systems. This study examines various performance metrics such as endurance, energy consumption, and switching characteristics to elucidate how these parameters are influenced by the unique characteristics of the respective materials. By examining both oxide- and 2D-material-based memristors in array configurations, this review provides insights into their suitability for neuromorphic computing, highlighting advancements, challenges, and future research directions in memristor technology.