Browsing by Author "Utkarsh S. Pandey"

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Fabrication of a solution-processed low voltage TFT by using colloid 2D ZnO nanosheets and its application as a UV photodetector
(Royal Society of Chemistry, 2025) Abhik Bhuin; Akhilesh Kumar Yadav; Utkarsh S. Pandey; Debdyuti Mukherjee; Vivek Kumar Agrahari; Caroline Ponraj; Subha Sadhu; Bhola Nath Pal; Sujoy Sarkar
ZnO nanostructures have been extensively employed in optoelectronic devices because of their unique optoelectronic properties; however, these devices have been developed using physical vapor deposition techniques, which are costly and need a state-of-the-art fabrication facility. Hence, a solution-processed, cost-effective, low-temperature method is required for the large-scale fabrication of 2D material-based electronic devices. In this contribution, we report template, polymer, and surfactant-free wet chemical synthesis of 2D ZnO nanostructures having dimensions of ∼200 nm and thickness of ∼30 nm following the hydrothermal method. Detailed structural, morphological, and optical investigation revealed the formation of a pure hexagonal wurtzite phase of ZnO nanosheets. Utilizing the as-synthesized nanosheets, solution-processed thin film transistors (TFTs) are fabricated under low annealing temperatures that exhibit a high carrier mobility of 8.05 cm2 V−1 s−1 and an on-off ratio of ∼105. Also, these TFTs show high photosensitivity and can be used as UV detectors. Thus, our study highlights low-temperature facile fabrication of 2D ZnO TFTs, which may have promising applications in electronic displays, logic circuits, UV detectors, biosensors, and portable electronics. © 2025 The Royal Society of Chemistry.
Fabrication of Schottky Barrier Oxide Transistors to Reduce Subthreshold Swing Close to the Theoretical Limits
(John Wiley and Sons Inc, 2025) Utkarsh S. Pandey; Akhilesh Kumar Yadav; Pijush Kanti Aich; Rajarshi Chakraborty; Sandeep Dahiya; Bhola Nath Pal
The nature of the contact between the semiconductor channel and metal electrodes have a great influence on the functionality of a thin film transistor (TFT). A Schottky barrier of such contact can originate a ‘thermionic emission and thermionic field emission’ limited current transport that can reduce the sub-threshold swing of a TFT largely. This attribution has been dealt with using an asymmetric work-function source-drain (S-D) electrode of a low operating voltage TFT. Furthermore, the performance of the device can be optimized by incorporating a suitable interface layer with an optimal thickness in the asymmetric work-function S-D electrode configuration. In this study, a ZnO TFT has been fabricated by using a LiInSnO4 gate dielectric that reduces its operating voltage to 2 V due to the high areal capacitance of the ionic gate dielectric. In this TFT, LiF/Al serves as the source electrode, while MoO3/Ag works as the drain electrode with variable thickness of the MoO3 layer. Notably, by adjusting the thickness of the MoO3 layer within the MoO3/Ag electrode, the subthreshold swing of the TFT achieved 66 mV/decade, which is close to the theoretical limit of subthreshold swing for oxide TFTs. © 2025 Wiley-VCH GmbH.
Piezopotential Gated Self-Biased Conducting Polymer-Based Flexible Transistor for Mechanical Energy Harvesting Device
(American Chemical Society, 2025) Utkarsh S. Pandey; Sandeep Dahiya; Rajarshi Chakraborty; Subarna Pramanik; Sobhan Hazra; Bhola Nath Pal
A self-biased thin-film transistor (TFT) has been fabricated by using poly(3, 4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) as a conducting channel that works as an efficient mechanical energy harvesting device. The self-biasing of this top-gated TFT has been accomplished through the integration of two voltage sources within the device structure, which are essential for its operation. The LiF/Al and MoO3/Ag electrodes serve as the source and drain, respectively, of this TFT that has a work-function difference of ∼−1.16 eV, which works as the drain bias (VD). The poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) thin film that has been employed as a gate dielectric generates a piezo-potential due to the application of external pressure and works as gate bias (VG) of this TFT. The unique feature of this device is its prolonged electrical power generation in DC form during the application of mechanical force that enables us to measure its mechanical-to-electrical power conversion energy accurately. The extracted power conversion efficiencies of hard and flexible (flat) substrate-based TFTs are 0.4 and 1.9%, respectively. Interestingly, the conversion efficiency of a flexible TFT increases with bending and can reach up to 33% which is unusually high for a mechanical energy harvesting device. In addition, electrical characterization of these devices shows transistor-like behavior with an On-Off ratio and subthreshold swing of 2 × 102 and 5.88 N/decade, respectively, for hard substrate, while on a flexible substrate, these values are 1 × 104 and 1.35 N/decade, respectively. © 2025 American Chemical Society.
Self-biased silicon transistor with a piezoelectric gate for an efficient mechanical energy harvesting device
(Royal Society of Chemistry, 2025) Utkarsh S. Pandey; Nila Pal; Sandeep Dahiya; Sobhan Hazra; Bhola Nath Pal
In this study, a piezo potential gated self-biased transistor was fabricated on a heavily doped silicon (p+-Si) (111) substrate and used for efficient mechanical energy harvesting applications. The drain and source (S-D) electrode of this top gated transistor was made of LiF(5 nm)/Al(65 nm) and MoO3(5 nm)/Ag(65 nm), respectively, whereas piezoelectric poly (vinylidene fluoride-co-hexapropelene) (PVDF-HFP) thin film was used as the gate dielectric. Drain bias (VDS), which was required to transport the hole carrier through the channel, was developed from the work function difference of the S-D electrodes, whereas the piezopotential, which worked as the gate bias of this transistor, was developed from the external force applied on the PVDF-HFP thin film. Consequently, this device efficiently converted mechanical energy into electrical energy. For an applied pressure of 4 bar for ∼5 s, the extracted electrical power per cycle of this device was 1.6 × 10−9 watts with a conversion efficiency of ∼75%, which was an exceptionally high value compared with conventional energy harvesting devices. Besides, the electrical characterization showed its transistor-like behavior, and the extracted device parameters, including threshold force, on-off ratio, and subthreshold swing (SS), were 0.5 N, 4.56 × 102, and 3.16 N A−1, respectively. © 2025 The Royal Society of Chemistry.
Synthesis of ZnO Quantum Dots and Their Applications in UV-Sensitive Low-Voltage Phototransistors
(American Chemical Society, 2025) Utkarsh S. Pandey; Sakhi Tiwari; Rajarshi Chakraborty; Sudip Kumar Batabyal; Bhola Nath Pal
ZnO quantum dots have been synthesized through a low-cost solution process with less complexity. The solution-processed quantum dots (QDs) demonstrate excellent stability and dispersion with an average crystallite size of ∼4.1 nm, which has been determined through the transmission electron microscopy and X-ray diffraction pattern. Furthermore, these ZnO QDs have also been utilized as a semiconductor channel in a solution-processed low-voltage (≤2 V) thin-film transistor (TFT) where ion-conducting LiInSnO4 thin film has been used as a gate dielectric. The fabricated ZnO QD-based TFT showcases saturation mobility (μsat), on/off ratio, and a subthreshold swing (SS) of 0.6 cm2/V sec, 104, and 166 mV/decade under dark conditions. Besides, using asymmetric work function source and drain electrodes, the on/off ratio and SS of the devices have been improved that effectively improves the UV sensitivity of the device. Under 1 W m-2 UV illumination, this asymmetric source-drain electrode TFT exhibits impressive UV photosensitivity with an external quantum efficiency of ∼25% which is comparably high for an UV phototransistor device. © 2025 American Chemical Society.