Browsing by Author "Sandeep Dahiya"

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A highly responsive UV photodetector based on WO3–ZnO layered thin film
(Elsevier B.V., 2025) Richa Kumari; A. Sameer Ruban Kumar; Sandeep Dahiya; Sanjay Kumar Srivastava; Debanjan Guin; Chandra Shekhar Pati Tripathi
This work focuses on the development of a heterostructure ultraviolet photodetector constructed using tungsten oxide (WO3) nanosheets (NSs) and zinc oxide (ZnO) nanoparticles (NPs), fabricated on Si/SiO2 substrates. For synthesis, a simple, economically feasible hydrothermal for WO3 and sol-gel synthesis approach for ZnO was used. The WO3 NSs/ZnO NPs heterostructure thin-film UV photodetector demonstrates excellent performance, including high responsivity (R), and detectivity (D) of 97.55 A/W, and 6.5 × 1011 Jones, respectively, when exposed to UV light (λ ∼ 365 nm). The working mechanism of the fabricated photodetector explained using a suitable energy band diagram. The WO3 NSs/ZnO NPs heterostructure thin-film UV photodetector exhibits a satisfactory response time, with a rise time of 5.35 s and a fall time of 10.24 s. © 2025 Elsevier B.V.
Enhancement in photo-response of CuZnS nanocrystals-based photodetector using asymmetric work function electrodes
(Elsevier B.V., 2024) Sandeep Dahiya; Sobhan Hazra; Utkarsh Pandey; Subarna Pramanik; Pardeep Dahiya; Satya Veer Singh; Nikita Kumari; Bhola Nath Pal
In this study, an efficient visible light photodetector has been fabricated by using heavy metal-free CuZnS Nanocrystals with average particle size of 13 ± 1 nm and has been synthesized by a microwave (MW) assisted synthesis technique. The optical band gap of this nanocrytstal is ∼1.7 eV and has an absorbance spectra ranging from 300 to700 nm. This low bandgap nanocrystals has been used to fabricate a photoconductor device with a CuZnS/ZnO bilayer structure. Besides, the device performance has been enhanced by using an asymmetric work-function lateral electrodes. The work-function difference between the electrodes gives a driven voltage between the electrodes, which allows faster collection of charge carriers from the device. As a consequence, a significant photocurrent is generated by the device even without any external bias. The self-biased (at 0 V) external quantum efficiency (EQE) of this device is ∼ 4 % (at 430 nm) whereas this value reaches ∼ 20 % under 2 V external bias. The device possesses the responsivity (Rλ) and detectivity (D) of 8.8 A/W and 3.8 × 1012 Jones at 320 nm respectively under 2 V external bias. © 2024 Elsevier B.V.
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.
Functionalized jute with high-water absorption, low thermal conductivity and efficient radiative cooling for the preservation of perishable green vegetables with reduced cold storage energy requirements
(Royal Society of Chemistry, 2024) Smruti B. Bhatt; Rahul Ranjan; Sandeep Dahiya; Bhola Nath Pal; Prodyut Dhar
Jute bags, traditionally used for storing fruits, vegetables and cereals, lack temperature resilience and catch fire, making the contents inside the bag vulnerable to deterioration. In this study, normal jute fibres (NJFs) were strategically modified via a delignification-cum-phosphorylation route to produce phosphorylated jute fibres (PJFs) using low-cost agro-based chemicals. PJFs exhibit a high water absorption capacity and a lower evaporation rate with prolonged moisture retention capabilities. Interestingly, PJFs also show an ultra-low thermal conductivity of 0.076-0.078 W m−1 K−1, slow rate of burning (0.058 cm s−1), high reflectance to light in the IR region (76%) and high thermal stability. PJF bags used for the storage of perishable vegetables, such as coriander leaves, show an extension in shelf life by ∼2 days, along with flame resistance to heat-sensitive vegetables such as chilies on exposure to high temperature. Life cycle assessment (LCA) shows that the production of PJFs generates 49.4% less global warming potential impact as compared to PET production with improved biodegradation within ∼21 days. Further, the utilization of PJFs reduced the time for cold storage of coriander leaves to 8 days, which led to reduced energy requirements and lowered environmental impacts by 11% in the terrestrial ecotoxicity and climate change category. The present study provides a strategic, scalable and green route for the production of functionalized jute bags required for the storage of perishable agricultural harvests, reducing global issues associated with food loss and improving human health and the economy. © 2024 The Royal Society of Chemistry.
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.
Solution-Processed ZnO/V2O5Heterojunction Thin Films for UV Photodetectors
(American Chemical Society, 2025) Prateek Kumar Yadav; Sandeep Dahiya; Bhola Nath Pal; Amit Kumar Srivastava; Amritanshu Pandey; Sanjay Kumar Srivastava
This study delineates the fabrication and evaluation of a high-performing ultraviolet (UV) photodetector (PD) consisting of a ZnO/V2O5nanoparticle (NP) bilayer thin film deposited on a Si/SiO2substrate through spin coating. Various analytical techniques, such as X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy, have been employed to investigate the structural features and surface morphology of the as-prepared samples. The V2O5NPs were prepared through a facile one-pot solvothermal process, while ZnO NPs were obtained through a rapid sol–gel method. V2O5NPs demonstrate extended absorption with significant absorption in the range of 240–450 nm and exhibit a relatively smaller band gap. The optoelectronic features of as-deposited thin films have primarily been studied through I–V characteristics under dark and UV light conditions with the same external bias of 2 V, and the photocurrent has been found to be 9.13 × 10–5A/cm2, which is ∼2.77 × 103times higher than the dark current. The obtained photocurrent-to-dark current ratio for the ZnO/V2O5device is nearly ∼1.37 × 102times higher than that of the ZnO-only device. Moreover, this bilayer UV PD exhibits a detectivity (D) of ∼3.1 × 1012Jones, a spectral responsivity (R) of ∼4 A/W, and an external quantum efficiency (EQE) of ∼16% under an external potential of 10 V. Furthermore, the findings are analyzed, and an explanation of the detailed photodetection mechanism is outlined in this paper. © 2025 American Chemical Society
Structural, Optical, and Electronic Properties of NixCd1–xS Quantum Dots: Implications for Photodetection Applications
(American Chemical Society, 2025) Nikita Kumari; Sandeep Dahiya; Chetna Gautam; Piyali Maity; Sandip Chatterjee; Bhola Nath Pal; Anup Kumar Ghosh
X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to study the structural and morphological characteristics of pure and Ni-doped CdS (CdS:Nix) (x = 0–6 atomic %) QDs synthesized via the hydrothermal method. Inductively coupled plasma mass spectrometry (ICP-MS) and EDS measurements have been carried out for quantifying the elemental composition. Due to Ni-doping, the short-range structural disorder causes a significant variation in the intensity of the longitudinal optical (LO) modes of Raman spectra. Optical absorption has been broadened with Ni doping, resulting in a reduction of the band gap from 2.42 eV (for CdS) to 2.36 eV (for CdS:Ni6). Photoluminescence (PL) spectra show various peaks associated with surface defects, near band emission (NBE), sulfur vacancies, photoinduced charge carrier separation, and recombination processes. To investigate the chemical states and valence band spectra of Ni-doped CdS QDs, X-ray photoemission spectroscopy (XPS) has been utilized. To realize their applicability in electronic devices, bilayer heterostructure photodetectors (PDs) have been fabricated on the glass substrate by using CdS:Nix QDs and sol–gel-derived SnO2(as a charge transport layer), viz., Glass/SnO2/CdS:Nix QD PDs. The performance of the device has been improved with a Ni-doping concentration in CdS QDs. The optimized device has been achieved with high photocurrent (28.2 mA/cm2), high figure-of-merit performance having a responsivity of 2.23 A/W, and detectivity of 2.1 × 1013Jones at a wavelength of approximately 450 nm under 5 V external bias for CdS:Ni6 QD heterostructure PD. Furthermore, this PD shows good response kinetics and are quite stable over time indicating its operational stability. © 2025 American Chemical Society