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1. Impact of Post‐Lithography Polymer Residue on the Electrical Characteristics of MoS 2 and WSe 2 Field Effect Transistors

   https://doi.org/10.1002/admi.201801321  

   Liang, Jierui ; Xu, Ke ; Toncini, Blaec ; Bersch, Brian ; Jariwala, Bhakti ; Lin, Yu‐Chuan ; Robinson, Joshua ; Fullerton‐Shirey, Susan K. ( December 2018 , Advanced Materials Interfaces)

   The residue of common photo‐ and electron‐beam resists, such as poly(methyl methacrylate) (PMMA), is often present on the surface of 2D crystals after device fabrication. The residue degrades device properties by decreasing carrier mobility and creating unwanted doping. Here, MoS₂and WSe₂field effect transistors (FETs) with residue are cleaned by contact mode atomic force microscopy (AFM) and the impact of the residue on: 1) the intrinsic electrical properties, and 2) the effectiveness of electric double layer (EDL) gating are measured. After cleaning, AFM measurements confirm that the surface roughness decreases to its intrinsic state (i.e., ≈0.23 nm for exfoliated MoS₂and WSe₂) and Raman spectroscopy shows that the characteristic peak intensities (E_2gand A_1g) increase. PMMA residue causes p‐type doping corresponding to a charge density of ≈7 × 10¹¹cm⁻²on back‐gated MoS₂and WSe₂FETs. For FETs gated with polyethylene oxide (PEO)₇₆:CsClO₄, removing the residue increases the charge density by 4.5 × 10¹²cm⁻², and the maximum drain current by 247% (statistically significant,p< 0.05). Removing the residue likely allows the ions to be positioned closer to the channel surface, which is essential for achieving the best possible electrostatic gate control in ion‐gated devices.

    

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2. Ultrathin quasi-2D amorphous carbon dielectric prepared from solution precursor for nanoelectronics

   https://doi.org/10.1038/s44172-023-00141-9  

   An, Fufei ; Wang, Congjun ; Pham, Viet Hung ; Borisevich, Albina ; Qian, Jiangchao ; Yin, Kaijun ; Pidaparthy, Saran ; Robinson, Brian ; Chou, Ang-Sheng ; Lee, Junseok ; et al ( December 2023 , Communications Engineering)

   Materials keeping thickness in atomic scale but extending primarily in lateral dimensions offer properties attractive for many emerging applications. However, compared to crystalline counterparts, synthesis of atomically thin films in the highly disordered amorphous form, which avoids nonuniformity and defects associated with grain boundaries, is challenging due to their metastable nature. Here we present a scalable and solution-based strategy to prepare large-area, freestanding quasi-2D amorphous carbon nanomembranes with predominant sp²bonding and thickness down to 1–2 atomic layers, from coal-derived carbon dots as precursors. These atomically thin amorphous carbon films are mechanically strong with modulus of 400 ± 100 GPa and demonstrate robust dielectric properties with high dielectric strength above 20 MV cm⁻¹and low leakage current density below 10⁻⁴ A cm⁻²through a scaled thickness of three-atomic layers. They can be implemented as solution-deposited ultrathin gate dielectrics in transistors or ion-transport media in memristors, enabling exceptional device performance and spatiotemporal uniformity.

    

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3. Mitigating Heavy Ion Irradiation‐Induced Degradation in p‐type SnO Thin‐Film Transistors at Room Temperature

   https://doi.org/10.1002/pssa.202300392  

   Al-Mamun, Nahid Sultan ; Rasel, Md Abu Jafar ; Wolfe, Douglas E. ; Haque, Aman ; Schoell, Ryan ; Hattar, Khalid ; Ryu, Seung Ho ; Kim, Seong Keun ( September 2023 , physica status solidi (a))

   The study investigates the mitigation of radiation damage on p‐type SnO thin‐film transistors (TFTs) with a fast, room‐temperature annealing process. Atomic layer deposition is utilized to fabricate bottom‐gate TFTs of high‐quality p‐type SnO layers. After 2.8 MeV Au⁴⁺irradiation at a fluence level of 5.2 × 10¹² ions cm⁻², the output drain current and on/off current ratio (I_on/I_off) decrease by more than one order of magnitude, field‐effect mobility (μ_FE) reduces more than four times, and subthreshold swing (SS) increases more than four times along with a negative shift in threshold voltage. The observed degradation is attributed to increased surface roughness and defect density, as confirmed by scanning electron microscopy (SEM), high‐resolution micro‐Raman, and transmission electron microscopy (TEM) with geometric phase analysis (GPA). A technique is demonstrated to recover the device performance at room temperature and in less than a minute, using the electron wind force (EWF) obtained from low‐duty‐cycle high‐density pulsed current. At a pulsed current density of 4.0 × 10⁵ A cm⁻², approximately four times increase inI_on/I_offis observed, 41% increase inμ_FE, and 20% decrease in the SS of the irradiated TFTs, suggesting effectiveness of the new annealing technique.

    

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4. Few‐Layer GeAs Field‐Effect Transistors and Infrared Photodetectors

   https://doi.org/10.1002/adma.201705934  

   Guo, Jian ; Liu, Yuan ; Ma, Yue ; Zhu, Enbo ; Lee, Shannon ; Lu, Zixuan ; Zhao, Zipeng ; Xu, Changhao ; Lee, Sung‐Joon ; Wu, Hao ; et al ( April 2018 , Advanced Materials)

   The family of 2D semiconductors (2DSCs) has grown rapidly since the first isolation of graphene. The emergence of each 2DSC material brings considerable excitement for its unique electrical, optical, and mechanical properties, which are often highly distinct from their 3D counterparts. To date, studies of 2DSC are majorly focused on group IV (e.g., graphene, silicene), group V (e.g., phosphorene), or group VIB compounds (transition metal dichalcogenides, TMD), and have inspired considerable effort in searching for novel 2DSCs. Here, the first electrical characterization of group IV–V compounds is presented by investigating few‐layer GeAs field‐effect transistors. With back‐gate device geometry, p‐type behaviors are observed at room temperature. Importantly, the hole carrier mobility is found to approach 100 cm²V⁻¹s⁻¹with ON–OFF ratio over 10⁵, comparable well with state‐of‐the‐art TMD devices. With the unique crystal structure the few‐layer GeAs show highly anisotropic optical and electronic properties (anisotropic mobility ratio of 4.8). Furthermore, GeAs based transistor shows prominent and rapid photoresponse to 1.6 µm radiation with a photoresponsivity of 6 A W⁻¹and a rise and fall time of ≈3 ms. This study of group IV–V 2DSC materials greatly expands the 2D family, and can enable new opportunities in functional electronics and optoelectronics based on 2DSCs.

    

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5. Seamless Fabrication and Threshold Engineering in Monolayer MoS 2 Dual‐Gated Transistors via Hydrogen Silsesquioxane

   https://doi.org/10.1002/aelm.201800888  

   Nasr, Joseph R. ; Das, Saptarshi ( February 2019 , Advanced Electronic Materials)

   From its inception, extensive work on the characterization of field effect transistors (FETs) based on 2D‐layered semiconductors has relied on a back‐gated transistor architecture. This is useful for initial assessment but lacks ultimate compatibility with integrated circuit (IC) design since the threshold voltage of individual devices cannot be controlled independently in order to achieve specific ON‐state and OFF‐state performance. Note that threshold engineering via gate electrostatics is inevitable for 2D semiconductors owing to the absence of comprehensive, reliable, and universal doping schemes. In recent years, several strategies are adopted for the gating of individual 2D‐FETs such as atomic layer deposition (ALD) of high‐kdielectrics, drop casting of ionic liquids, and deterministic transfer of insulating 2D hexagonal boron nitride. These techniques have their respective strengths and weaknesses. A facile, low‐temperature, scalable, and universally applicable fabrication scheme for dual‐gated monolayer 2D‐FETs is reported here, which is compatible with the back‐end‐of‐the‐line (BEOL) process flow of complementary metal oxide semiconductor (CMOS) technology, using hydrogen silsesquioxane (HSQ). HSQ is a negative tone resist that possesses dielectric properties similar to SiO₂when exposed to high electron beam irradiation and thermal curing and can produce features as small as 10 nm.

    

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