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1. Improved Crystallization of Lead Halide Perovskite in Two‐Step Growth Method by Polymer‐Assisted “Slow‐Release Effect”

   https://doi.org/10.1002/smtd.202201663  

   Lin, Siyuan; Wu, Shuyue; Guo, De'en; Huang, Han; Zhou, Xuefan; Zhang, Dou; Zhou, Kechao; Zhang, Wenhao; Hu, Yue; Gao, Yongli; et al (April 2023, Small Methods)

   Abstract Fast reaction between organic salt and lead iodide always leads to small perovskite crystallites and concentrated defects. Here, polyacrylic acid is blended with organic salt, so as to regulate the crystallization in a two‐step growth method. It is observed that addition of polyacrylic acid retards aggregation and crystallization behavior of the organic salt, and slows down the reaction rate between organic salt and PbI 2 , by which “slow‐release effect” is defined. Such effect improves crystallization of perovskite. X‐ray diffraction study shows that, after addition of 2 m m polyacrylic acid, average crystallite size of perovskite increases from ≈40 to ≈90 nm, meanwhile, grain size increases. Thermal admittance spectroscopy study shows that trap density is reduced by nearly one order (especially for deep energy levels). Due to the improved crystallization and reduced trap density, charge recombination is obviously reduced, while lifetime of charge carriers in perovskite film and devices are prolonged, according to time‐resolved photoluminescence and transient photo‐voltage decay curve tests, respectively. Accordingly, power conversion efficiency of the device is promoted from 19.96 (±0.41)% to 21.84 (±0.25)% (with a champion efficiency of 22.31%), and further elevated to 24.19% after surface modification by octylammonium iodide. 

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2. Reducing Trap States in Printed Indium Zinc Oxide Transistors by Doping with Benzyl Viologen

   https://doi.org/10.1002/aelm.201700631  

   Kim, Hyonwoong; Ng, Tse Nga (April 2018, Advanced Electronic Materials)

   An air‐stable, strongly reducing molecule benzyl viologen (BV) is used to induce charge‐transfer doping of the indium zinc oxide semiconductor in inkjet‐printed thin‐film transistors. The device mobility is improved from 5.8 ± 1.4 cm^2 V^−1 s^−1 in the undoped devices and reached up to 8.7 ± 1.0 cm^2 V^−1 s^−1 after BV treatment. Through measurement of frequency‐dependent admittance and capacitance, this work quantifies the density of interface states and shows that interfacial trap density is four times lower in the BV‐doped transistors compared to undoped devices. 

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3. Influence of Rhenium Concentration on Charge Doping and Defect Formation in MoS ₂

   https://doi.org/10.1002/aelm.202400403  

   Munson, Kyle T; Torsi, Riccardo; Habis, Fatimah; Huberich, Lysander; Lin, Yu‐Chuan; Yuan, Yue; Wang, Ke; Schuler, Bruno; Wang, Yuanxi; Asbury, John B; et al (March 2025, Advanced Electronic Materials)

   Substitutionally doped transition metal dichalcogenides (TMDs) are essential for advancing TMD‐based field effect transistors, sensors, and quantum photonic devices. However, the impact of local dopant concentrations and dopant–dopant interactions on charge doping and defect formation within TMDs remains underexplored. Here, a breakthrough understanding of the influence of rhenium (Re) concentration is presented on charge doping and defect formation in MoS₂monolayers grown by metal–organic chemical vapor deposition (MOCVD). It is shown that Re‐MoS₂films exhibit reduced sulfur‐site defects, consistent with prior reports. However, as the Re concentration approaches ⪆2 atom%, significant clustering of Re in the MoS₂is observed. Ab Initio calculations indicate that the transition from isolated Re atoms to Re clusters increases the ionization energy of Re dopants, thereby reducing Re‐doping efficacy. Using photoluminescence (PL) spectroscopy, it is shown that Re dopant clustering creates defect states that trap photogenerated excitons within the MoS₂lattice, resulting in broad sub‐gap emission. These results provide critical insights into how the local concentration of metal dopants influences carrier density, defect formation, and exciton recombination in TMDs, offering a novel framework for designing future TMD‐based devices with improved electronic and photonic properties. 

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4. Enhanced photocurrent response speed in charge-density-wave phase of TiSe ₂ -metal junctions

   https://doi.org/10.1039/D1NR01810H  

   Walmsley, Thayer S.; Xu, Ya-Qiong (January 2021, Nanoscale)

   null (Ed.)

   Group IVB transition metal dichalcogenides (TMDCs) have attracted significant attention due to their predicted high charge carrier mobility, large sheet current density, and enhanced thermoelectric power. Here, we investigate the electrical and optoelectronic properties of few-layer titanium diselenide (TiSe 2 )-metal junctions through spatial-, wavelength-, temperature-, power- and temporal-dependent scanning photocurrent measurements. Strong photocurrent responses have been detected at TiSe 2 -metal junctions, which is likely attributed to both photovoltaic and photothermoelectric effects. A fast response time of 31 μs has been achieved, which is two orders of magnitude better than HfSe 2 based devices. More importantly, our experimental results reveal a significant enhancement in the response speed upon cooling to the charge-density-wave (CDW) phase transition temperature ( T CDW = 206 K), which may result from dramatic reduction in carrier scattering that occurs as a result of the switching between the normal and CDW phases of TiSe 2 . Additionally, the photoresponsivity at 145 K is up to an order of magnitude higher than that obtained at room temperature. These fundamental studies not only offer insight for the photocurrent generation mechanisms of group IVB TMDC materials, but also provide a route to engineering future temperature-dependent, two-dimensional, fast electronic and optoelectronic devices. 

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5. Reducing proton radiation vulnerability in AlGaN/GaN high electron mobility transistors with residual strain relief

   https://doi.org/10.1063/5.0169886  

   Al-Mamun, Nahid Sultan; Bae, Joonyup; Kim, Jihyun; Haque, Aman; Wolfe, Douglas E.; Ren, Fan; Pearton, Stephen J. (December 2023, Journal of Applied Physics)

   Strain plays an important role in the performance and reliability of AlGaN/GaN high electron mobility transistors (HEMTs). However, the impact of strain on the performance of proton irradiated GaN HEMTs is yet unknown. In this study, we investigated the effects of strain relaxation on the properties of proton irradiated AlGaN/GaN HEMTs. Controlled strain relief is achieved locally using the substrate micro-trench technique. The strain relieved devices experienced a relatively smaller increase of strain after 5 MeV proton irradiation at a fluence of 5 × 1014 cm−2 compared to the non-strain relieved devices, i.e., the pristine devices. After proton irradiation, both pristine and strain relieved devices demonstrate a reduction of drain saturation current (Ids,sat), maximum transconductance (Gm), carrier density (ns), and mobility (μn). Depending on the bias conditions the pristine devices exhibit up to 32% reduction of Ids,sat, 38% reduction of Gm, 15% reduction of ns, and 48% reduction of μn values. In contrast, the strain relieved devices show only up to 13% reduction of Ids,sat, 11% reduction of Gm, 9% reduction of ns, and 30% reduction of μn values. In addition, the locally strain relieved devices show smaller positive shift of threshold voltage compared to the pristine devices after proton irradiation. The less detrimental impact of proton irradiation on the transport properties of strain relieved devices could be attributed to reduced point defect density producing lower trap center densities, and evolution of lower operation related stresses due to lower initial residual strain. 

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