Browsing by Author "Shafi, Abde Mayeen"

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  • Broadband miniaturized spectrometers with a van der Waals tunnel diode
    (2024-01-17) Uddin, Md Gius; Das, Susobhan; Shafi, Abde Mayeen; Wang, Lei; Cui, Xiaoqi; Nigmatulin, Fedor; Ahmed, Faisal; Liapis, Andreas C.; Cai, Weiwei; Yang, Zongyin; Lipsanen, Harri; Hasan, Tawfique; Yoon, Hoon Hahn; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Miniaturized spectrometers are of immense interest for various on-chip and implantable photonic and optoelectronic applications. State-of-the-art conventional spectrometer designs rely heavily on bulky dispersive components (such as gratings, photodetector arrays, and interferometric optics) to capture different input spectral components that increase their integration complexity. Here, we report a high-performance broadband spectrometer based on a simple and compact van der Waals heterostructure diode, leveraging a careful selection of active van der Waals materials- molybdenum disulfide and black phosphorus, their electrically tunable photoresponse, and advanced computational algorithms for spectral reconstruction. We achieve remarkably high peak wavelength accuracy of ~2 nanometers, and broad operation bandwidth spanning from ~500 to 1600 nanometers in a device with a ~ 30×20 μm2 footprint. This diode-based spectrometer scheme with broadband operation offers an attractive pathway for various applications, such as sensing, surveillance and spectral imaging.
  • Configurable anti-ambipolar photoresponses for optoelectronic multi-valued logic gates
    (2024-07-29) Cui, Xiaoqi; Kim, Sunmean; Ahmed, Faisal; Du, Mingde; Liapis, Andreas C.; Muñoz, Juan Arias; Shafi, Abde Mayeen; Uddin, Md Gius; Ali, Fida; Zhang, Yi; Kang, Dong Ho; Lipsanen, Harri; Kang, Seokhyeong; Yoon, Hoon Hahn; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Anti-ambipolar transistors (AATs) are the leading platform for the paradigm shift from binary to multi-valued logic (MVL) circuits, increasing circuit integration density and data processing capacity. However, most AATs with p-n heterojunctions present limited controllability of the transconductance peak, which is key to MVL operation. Here, we report optically configurable AAT/bi-AAT photoresponses implemented with an InSe field-effect transistor for potential MVL operations. The charge trapping and detrapping processes incorporated with manually introduced trap states form the AAT peaks. Furthermore, leveraging a symmetric device configuration, the dark current is significantly suppressed, and AAT photoresponses are highlighted. Contributed by two pathways of trap states, the AAT/bi-AAT photoresponses are switchable by incident optical wavelength. This dependence facilitates optical wavelength to be one of the logic inputs for MVL, based on which we propose circuit-free ternary logic gates in a single device that can achieve more than ∼ 6 and ∼ 19 times improved data density (1 bit per transistor) for NMAX and XNOR, compared with such circuits in a traditional binary design. This work realizes optically controlled AAT photoresponses, paving the way to exploit optical wavelength as a new degree of freedom in MVL computing, offering a route toward ultra-high-density, ultra-low-power, and optically programmable optoelectronic integrated circuits.
  • Deterministic Polymorphic Engineering of MoTe2 for Photonic and Optoelectronic Applications
    (2023-08-15) Ahmed, Faisal; Rodríguez-Fernández, Carlos; Fernandez, Henry A.; Zhang, Yi; Shafi, Abde Mayeen; Uddin, Md Gius; Cui, Xiaoqi; Yoon, Hoon Hahn; Mehmood, Naveed; Liapis, Andreas C.; Yao, Lide; Caglayan, Humeyra; Sun, Zhipei; Lipsanen, Harri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Developing selective and coherent polymorphic crystals at the nanoscale offers a novel strategy for designing integrated architectures for photonic and optoelectronic applications such as metasurfaces, optical gratings, photodetectors, and image sensors. Here, a direct optical writing approach is demonstrated to deterministically create polymorphic 2D materials by locally inducing metallic 1T′-MoTe2 on the semiconducting 2H-MoTe2 host layer. In the polymorphic-engineered MoTe2, 2H- and 1T′- crystalline phases exhibit strong optical contrast from near-infrared to telecom-band ranges (1–1.5 µm), due to the change in the band structure and increase in surface roughness. Sevenfold enhancement of third harmonic generation intensity is realized with conversion efficiency (susceptibility) of ≈1.7 × 10−7 (1.1 × 10−19 m2 V−2) and ≈1.7 × 10−8 (0.3 × 10−19 m2 V−2) for 1T′ and 2H-MoTe2, respectively at telecom-band ultrafast pump laser. Lastly, based on polymorphic engineering on MoTe2, a Schottky photodiode with a high photoresponsivity of 90 AW−1 is demonstrated. This study proposes facile polymorphic engineered structures that will greatly benefit realizing integrated photonics and optoelectronic circuits.
  • Direct Epitaxial Growth of InP Nanowires on MoS2 with Strong Nonlinear Optical Response
    (2022-10-25) Shafi, Abde Mayeen; Das, Susobhan; Khayrudinov, Vladislav; Uddin, Md Gius; Ding, Er-Xiong; Ahmed, Faisal; Sun, Zhipei; Lipsanen, Harri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Mixed-dimensional van der Waals heterostructures are promising for research and technological advances in photonics and optoelectronics. Here we report vapor-liquid-solid (VLS) method -based van der Waals epitaxy of one-dimensional InP nanowires (NWs) directly on two-dimensional MoS2. With optimized growth parameters (V/III ratio, flow rates of precursors, and growth temperature), we successfully grow high-quality InP NWs on MoS2. The density and vertical yield of NWs on MoS2 are significantly high. Due to the unique properties of both materials, we observe strong linear and nonlinear optical responses from the NW/MoS2 heterostructures. Intriguingly, in addition to strong second and third harmonic responses, the mixed-dimensional heterostructures show odd-order high harmonic generation up to seventh order. Our findings can open new possibilities for advancing attosecond physics on a new platform of mixed-dimensional heterostructures.
  • Engineering the Dipole Orientation and Symmetry Breaking with Mixed-Dimensional Heterostructures
    (2022-07-15) Uddin, Md Gius; Das, Susobhan; Shafi, Abde Mayeen; Khayrudinov, Vladislav; Ahmed, Faisal; Fernandez, Henry; Du, Luojun; Lipsanen, Harri; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Engineering of the dipole and the symmetry of materials plays an important role in fundamental research and technical applications. Here, a novel morphological manipulation strategy to engineer the dipole orientation and symmetry of 2D layered materials by integrating them with 1D nanowires (NWs) is reported. This 2D InSe –1D AlGaAs NW heterostructure example shows that the in-plane dipole moments in InSe can be engineered in the mixed-dimensional heterostructure to significantly enhance linear and nonlinear optical responses (e.g., photoluminescence, Raman, and second harmonic generation) with an enhancement factor of up to ≈12. Further, the 1D NW can break the threefold rotational symmetry of 2D InSe, leading to a strong optical anisotropy of up to ≈65%. These results of engineering dipole orientation and symmetry breaking with the mixed-dimensional heterostructures open a new path for photonic and optoelectronic applications.
  • Highly Sensitive MoS2 Photodetectors Enabled with a Dry-Transferred Transparent Carbon Nanotube Electrode
    (2023-01-25) Ding, Er-Xiong; Liu, Peng; Yoon, Hoon Hahn; Ahmed, Faisal; Du, Mingde; Shafi, Abde Mayeen; Mehmood, Naveed; Kauppinen, Esko I.; Sun, Zhipei; Lipsanen, Harri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fabricating electronic and optoelectronic devices by transferring pre-deposited metal electrodes has attracted considerable attention, owing to the improved device performance. However, the pre-deposited metal electrode typically involves complex fabrication procedures. Here, we introduce our facile electrode fabrication process which is free of lithography, lift-off, and reactive ion etching by directly press-transferring a single-walled carbon nanotube (SWCNT) film. We fabricated Schottky diodes for photodetector applications using dry-transferred SWCNT films as the transparent electrode to increase light absorption in photoactive MoS2 channels. The MoS2 flake vertically stacked with an SWCNT electrode can exhibit excellent photodetection performance with a responsivity of ∼2.01 × 103 A/W and a detectivity of ∼3.2 × 1012 Jones. Additionally, we carried out temperature-dependent current–voltage measurement and Fowler–Nordheim (FN) plot analysis to explore the dominant charge transport mechanism. The enhanced photodetection in the vertical configuration is found to be attributed to the FN tunneling and internal photoemission of charge carriers excited from indium tin oxide across the MoS2 layer. Our study provides a novel concept of using a photoactive MoS2 layer as a tunneling layer itself with a dry-transferred transparent SWCNT electrode for high-performance and energy-efficient optoelectronic devices.
  • Inducing Strong Light-Matter Coupling and Optical Anisotropy in Monolayer MoS2 with High Refractive Index Nanowire
    (2022-07-13) Shafi, Abde Mayeen; Ahmed, Faisal; Fernandez, Henry A.; Uddin, Md Gius; Cui, Xiaoqi; Das, Susobhan; Dai, Yunyun; Khayrudinov, Vladislav; Yoon, Hoon Hahn; Du, Luojun; Sun, Zhipei; Lipsanen, Harri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Mixed-dimensional heterostructures combine the merits of materials of different dimensions; therefore, they represent an advantageous scenario for numerous technological advances. Such an approach can be exploited to tune the physical properties of two-dimensional (2D) layered materials to create unprecedented possibilities for anisotropic and high-performance photonic and optoelectronic devices. Here, we report a new strategy to engineer the light-matter interaction and symmetry of monolayer MoS2 by integrating it with one-dimensional (1D) AlGaAs nanowire (NW). Our results show that the photoluminescence (PL) intensity of MoS2 increases strongly in the mixed-dimensional structure because of electromagnetic field confinement in the 1D high refractive index semiconducting NW. Interestingly, the 1D NW breaks the 3-fold rotational symmetry of MoS2, which leads to a strong optical anisotropy of up to ∼60%. Our mixed-dimensional heterostructure-based phototransistors benefit from this and exhibit an improved optoelectronic device performance with marked anisotropic photoresponse behavior. Compared with bare MoS2 devices, our MoS2/NW devices show ∼5 times enhanced detectivity and ∼3 times higher photoresponsivity. Our results of engineering light-matter interaction and symmetry breaking provide a simple route to induce enhanced and anisotropic functionalities in 2D materials.
  • Multilayer MoTe2 Field-Effect Transistor at High Temperatures
    (2021-11-23) Ahmed, Faisal; Shafi, Abde Mayeen; Mackenzie, David M.A.; Qureshi, Maaz Ahmed; Fernandez, Henry A.; Yoon, Hoon Hahn; Uddin, Md Gius; Kuittinen, Markku; Sun, Zhipei; Lipsanen, Harri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Functional 2D material-based devices are likely subjected to high ambient temperatures when integrated into miniaturized circuits for practical applications, which may induce irreversible structural changes in materials and impact the device performance. However, majority of 2D devices' studies focus on room temperature or low-temperature operation conditions. Here, the high-temperature (up to 673 K) electro-thermal response of molybdenum ditelluride (MoTe2) based field-effect transistors is investigated. The optimal annealing temperature of around 500-525 K for the multilayer MoTe2 devices with twofold enhancement in maximum current level, field-effect mobility, and current on-off ratio is identified. Furthermore, MoTe2 devices show the transition of electrical response from gate modulation to the degenerately p-doped (hole dominant) characteristics when the operation temperature increases to approximate to 600 K. The gate-dependent electro-thermal measurements complemented by surface chemistry analysis confirm the near range hopping transport in the MoTe2 channel at high temperature induced by thermally triggered oxidation of MoTe2. These results not only provide the thermal endurance limits of MoTe2 for practical applications, but also indicate the possible applications of MoTe2 for thermal sensing applications.
  • Photonic and Electronic Characterization of Two-dimensional Transition Metal Dichalcogenides
    (2023) Shafi, Abde Mayeen
     School of Electrical Engineering | Doctoral dissertation (article-based)
    Two-dimensional (2D) transition metal dichalcogenides (TMDCs) hold promise for numerous unprecedented applications in nanophotonics, optoelectronics, and nanoelectronics, owing to their extraordinary electrical and optical properties. However, these materials still face several challenges, including limited light-matter interactions, low luminescent yield, reduced carrier mobility, and susceptibility to environmental changes. This thesis aims to address the aforementioned limitations by employing various advanced techniques to enhance the optical and electronic properties of these materials. In this thesis, the light-matter interaction in TMDCs is enhanced by realizing mixed-dimensional heterostructures. High-performance photonic and optoelectronic devices are constructed by investigating two distinct types of these heterostructures. Firstly, monolayer MoS2 is transferred onto AlGaAs nanowires to create a mixed-dimensional heterostructure. A significant enhancement in Raman and photoluminescence responses is achieved from the heterostructure attributed to the electromagnetic field confinement within the high refractive index nanowire. The heterostructure also exhibits optical anisotropy due to the 3-fold rotational symmetry breaking of MoS2 caused by the nanowire. Additionally, the fabricated phototransistor using this heterostructure demonstrates improved responsivity and detectivity. Secondly, another mixed-dimensional heterostructure is formed by epitaxially growing InP nanowires directly on MoS2. High-density nanowire growth is achieved while ensuring the stability of MoS2. This heterostructure generates strong second- and third-harmonic signals and, notably, 5th and 7th-order high-harmonic signals, opening up potential applications such as lasers and electro-optic modulators. In the subsequent part of the thesis, the electronic properties of TMDCs are investigated and tuned to fabricate high-performance electronic and optoelectronic devices. At first, the impact of high temperatures on multilayer MoTe2 field-effect transistors is systematically explored to determine the optimal annealing temperature for the devices and acquire a deeper understanding of the surface oxidation-mediated defect formation and hopping transport mechanism in MoTe2 devices. Furthermore, a straightforward technique is proposed that involves substrate engineering and Al2O3 passivation to enhance the performance of few-layer MoTe2 devices by introducing local tensile strain and reducing electron-phonon scattering in the channel. This results in significant improvements in carrier mobility and device quality. Lastly, a simple optical writing technique is employed to transform the semiconducting 2H phase of MoTe2 into the metallic 1T´ phase, resulting in improved third harmonic generation signals and the performance of optoelectronic devices. These findings show great promise for advancing integrated photonic and optoelectronic circuits based on 2D-TMDCs.
  • Strain Engineering for Enhancing Carrier Mobility in MoTe2 Field-Effect Transistors
    (2023-10-17) Shafi, Abde Mayeen; Uddin, Md Gius; Cui, Xiaoqi; Ali, Fida; Ahmed, Faisal; Radwan, Mohamed; Das, Susobhan; Mehmood, Naveed; Sun, Zhipei; Lipsanen, Harri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Molybdenum ditelluride (MoTe2) exhibits immense potential in post-silicon electronics due to its bandgap comparable to silicon. Unlike other 2D materials, MoTe2 allows easy phase modulation and efficient carrier type control in electrical transport. However, its unstable nature and low-carrier mobility limit practical implementation in devices. Here, a deterministic method is proposed to improve the performance of MoTe2 devices by inducing local tensile strain through substrate engineering and encapsulation processes. The approach involves creating hole arrays in the substrate and using atomic layer deposition grown Al2O3 as an additional back-gate dielectric layer on SiO2. The MoTe2 channel is passivated with a thick layer of Al2O3 post-fabrication. This structure significantly improves hole and electron mobilities in MoTe2 field-effect transistors (FETs), approaching theoretical limits. Hole mobility up to 130 cm−2 V−1 s−1 and electron mobility up to 160 cm−2 V−1 s−1 are achieved. Introducing local tensile strain through the hole array enhances electron mobility by up to 6 times compared to the unstrained devices. Remarkably, the devices exhibit metal–insulator transition in MoTe2 FETs, with a well-defined critical point. This study presents a novel technique to enhance carrier mobility in MoTe2 FETs, offering promising prospects for improving 2D material performance in electronic applications.