Browsing by Author "Sajal Biring"

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Application of a microwave synthesized ultra-smooth a-C thin film for the reduction of dielectric/semiconductor interface trap states of anoxide thin film transistor
(Royal Society of Chemistry, 2022) Nila Pal; Baishali Thakurta; Rajarshi Chakraborty; Utkarsh Pandey; Vishwas Acharya; Sajal Biring; Monalisa Pal; Bhola N. Pal
In high-κ dielectric-based thin-film transistors (TFTs), tailoring the surface of the gate dielectric layer is a crucial issue for the improvement of the device performance. Herein, a simple solution-processed ultra-smooth amorphous-carbon (a-C) film is applied as a surface modification layer on the top of the high-κ ion-conducting Li-Al2O3 dielectric of a bottom gated SnO2 TFT. The a-C film minimizes the surface roughness of the gate dielectric and forms a strong coordination bond between the doped nitrogen of the a-C film and tin (Sn) of the upper lying SnO2 semiconducting channel, which lowers the gate leakage current, carrier scattering and trap state density at the dielectric/semiconductor interface successfully. As a consequence, the TFT with an a-C interface shows an improvement in the carrier mobility by 6.7 times with a higher ON/OFF ratio and a lower subthreshold swing (SS) by 3.8 times. An optimized device with an a-C gate interface shows a saturation carrier mobility, ON/OFF ratio and SS value of 21.1 cm2 V−1 s−1, 7.0 × 104, and 147 mV dec−1, respectively. Moreover, a significant improvement in the cycling electrical stability has been observed which is an outcome of a reduced trap state of an a-C modified TFT. © 2022 The Royal Society of Chemistry.
Ingenious Fabrication of Ag-Filled Porous Anodic Alumina Films as Powerful SERS Substrates for Efficient Detection of Biological and Organic Molecules
(MDPI, 2022) Chih-Yi Liu; Rahul Ram; Rahim Bakash Kolaru; Anindya Sundar Jana; Annada Sankar Sadhu; Cheng-Shane Chu; Yi-Nan Lin; Bhola Nath Pal; Shih-Hsin Chang; Sajal Biring
Surface-enhanced Raman scattering (SERS) has been widely used to effectively detect various biological and organic molecules. This detection method needs analytes adsorbed onto a specific metal nanostructure, e.g., Ag-nanoparticles. A substrate containing such a structure (called SERS substrate) is user-friendly for people implementing the adsorption and subsequent SERS detection. Here, we report on powerful SERS substrates based on efficient fabrication of Ag-filled anodic aluminum oxide (AAO) films. The films contain many nanopores with small as-grown inter-pore gap of 15 nm. The substrates are created by electrochemically depositing silver into nanopores without an additional pore widening process, which is usually needed for conventional two-step AAO fabrication. The created substrates contain well-separated Ag-nanoparticles with quite a small inter-particle gap and a high number density (2.5 × 1010 cm−2). We use one-step anodization together with omitting additional pore widening to improve the throughput of substrate fabrication. Such substrates provide a low concentration detection limit of 10−11 M and high SERS enhancement factor of 1 × 106 for rhodamine 6G (R6G). The effective detection of biological and organic molecules by the substrate is demonstrated with analytes of adenine, glucose, R6G, eosin Y, and methylene blue. These results allow us to take one step further toward the successful commercialization of AAO-based SERS substrates. © 2022 by the authors.
Selective near-infrared (NIR) photodetectors fabricated with colloidal CdS:Co quantum dots
(Royal Society of Chemistry, 2019) Piyali Maity; Satya Veer Singh; Sajal Biring; Bhola N. Pal; Anup K. Ghosh
Herein, cobalt-doped cadmium sulphide CdS (CdS:Co) quantum dots (QDs) were synthesized by an organometallic synthesis route using different doping concentrations of Co ranging from 1 to 8%. Optical absorption data indicate the appearance of a new NIR absorption peak of the QDs due to Co doping; moreover, the intensity of the peak increases with the doping concentration; this NIR absorption peak originates from the existence of a doping band located in close vicinity to the valence band inside the band gap. The electrical conductivities of the CdS:Co thin films 'in the dark' show increasing conductivity with doping concentration; this supports the enhancement of the carrier concentration in the valence/conduction band. In addition to the dark current, the photosensitivities of these CdS:Co QDs thin film increase gradually with doping, and significant enhancement was observed in the zinc oxide (ZnO) CdS:Co QD heterojunction structure. Lateral ZnO/CdS:Co heterojunction photodetectors with different doping concentrations of Co2+ show selective NIR sensitivity, which is not realized in the case of undoped CdS. The highest detectivity was observed for the 8% doped CdS:Co heterojunction photodetector, with the detectivity of 3.1 × 1011 Jones with illumination of 820 nm wavelength light under 5.0 V external bias, which is significantly high for an NIR photodetector. © 2019 The Royal Society of Chemistry.