Saravanan Rajamani

Bio: Saravanan Rajamani is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topics: Photodetector & Ion implantation. The author has an hindex of 8, co-authored 12 publications receiving 226 citations. Previous affiliations of Saravanan Rajamani include Roma Tre University.

Improved Sensitivity with Low Limit of Detection of a Hydrogen Gas Sensor Based on rGO-Loaded Ni-Doped ZnO Nanostructures.

Abstract: We report enhanced hydrogen-gas-sensing performance of a Ni-doped ZnO sensor decorated with the optimum concentration of reduced graphene oxide (rGO). Ni-doped ZnO nanoplates were grown by radio frequency sputtering, rGO was synthesized by Hummer’s method and decorated by the drop cast method of various concentration of rGO (0–1.5 wt %). The current–voltage characteristics of the rGO-loaded sensor are highly influenced by the loading concentration of rGO, where current conduction decreases and sensor resistance increases as the rGO concentration is increased up to 0.75 wt % because of the formation of various Schottky heterojunctions at rGO/ZnO interfaces. With the combined effect of more active site availability and formation of various p–n heterojunctions due to the optimum loading concentration of rGO (0.75 wt %), the sensor shows the maximum sensing response of ∼63.8% for 100 ppm hydrogen at moderate operating temperature (150 °C). The rGO-loaded sensors were able to detect a minimum of 1 ppm hydrogen...

Effect of self-heating on electrical characteristics of AlGaN/ GaN HEMT on Si (111) substrate

Abstract: In order to study the effect of self-heating of AlGaN/ GaN high electron mobility transistors (HEMTs) characteristics fabricated on Si(111) substrate, simulations of 2DEG temperature on different drain voltages have been carried out by Sentaurus TCAD simulator tool. Prior to the electrical direct-current (DC) characteristics studies, structural properties of the HEMT structures were examined by scanning transmission electron microscopy. The comparative analysis of simulation and experimental data provided sheet carrier concentration, mobility, surface traps, electron density at 2DEG by considering factors such as high field saturation, tunneling and recombination models. Mobility, surface trap concentration and contact resistance were obtained by TCAD simulation and found out to be ∼1270cm2/Vs, ∼2×1013 cm-2 and ∼0.2 Ω.mm, respectively, which are in agreement with the experimental results. Consequently, simulated current-voltage characteristics of HEMTs are in good agreement with experimental results. The ...

A high-performance hydrogen sensor based on a reverse-biased MoS 2/GaN heterojunction

Abstract: We report a MoS2/GaN heterojunction-based gas sensor by depositing MoS2 over a GaN substrate via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The microscopic and spectroscopic measurements expose the presence of highly crystalline and homogenous few atomic layer MoS2 on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS2/GaN interface under the reverse biased condition, thus resulting in high sensitivity. Our results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature (25-150 °C). For a deeper understanding of carrier dynamics at the heterointerface, we visualized the band alignment across the MoS2/GaN heterojunction having valence band and conduction band offset values of 1.75 and 0.28 eV. The sensing mechanism was demonstrated based on an energy band diagram at the MoS2/GaN interface in the presence and absence of hydrogen exposure. The proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes.

Efficient room temperature hydrogen sensor based on UV-activated ZnO nano-network.

Abstract: Room temperature hydrogen sensors were fabricated from Au embedded ZnO nano-networks using a 30 mW GaN ultraviolet LED. The Au-decorated ZnO nano-networks were deposited on a SiO2/Si substrate by a chemical vapour deposition process. X-ray diffraction (XRD) spectrum analysis revealed a hexagonal wurtzite structure of ZnO and presence of Au. The ZnO nanoparticles were interconnected, forming nano-network structures. Au nanoparticles were uniformly distributed on ZnO surfaces, as confirmed by FESEM imaging. Interdigitated electrodes (IDEs) were fabricated on the ZnO nano-networks using optical lithography. Sensor performances were measured with and without UV illumination, at room temperate, with concentrations of hydrogen varying from 5 ppm to 1%. The sensor response was found to be ∼21.5% under UV illumination and 0% without UV at room temperature for low hydrogen concentration of 5 ppm. The UV-photoactivated mode enhanced the adsorption of photo-induced O- and O2- ions, and the d-band electron transition from the Au nanoparticles to ZnO-which increased the chemisorbed reaction between hydrogen and oxygen. The sensor response was also measured at 150 °C (without UV illumination) and found to be ∼18% at 5 ppm. Energy efficient low cost hydrogen sensors can be designed and fabricated with the combination of GaN UV LEDs and ZnO nanostructures.

Boosting Sensing Performance of Vacancy-Containing Vertically Aligned MoS 2 Using rGO Particles

Abstract: A design of an advanced sensing material, such as MoS2, is imperative to enhance the sensing performance of a sensor. Because their usage alone for developing a practical sensor is impeditive owing to low gas response and slow response/recovery kinetics. Here, we report a high-performance NO2 gas sensor using a hybrid of temperature-assisted sulfur vacancy within the edge-oriented vertically aligned MoS2 (Sv-MoS2) and crumpled reduced graphene oxide (rGO) particles. Interestingly, the Sv-MoS2 functionalized by optimized rGO concentration exhibited a significant enhancement of response to NO2 (approximately three times higher than that of pristine vertically aligned MoS2) with fast response (< 1 min) and complete recovery. Such a large improvement in the sensing performance could be attributed to controlled electrical/chemical sensitization level of MoS2 through controllable vacancy and interface engineering. The vacancy engineering offers abundant active sites through creating sulfur vacancy in additionally rich edge active sites of vertically oriented MoS2 for more electronic interaction with gas molecules. While interfacing of p-type rGO particles with n-type MoS2 leads to multiple out-of-plane vertical nano-heterojunctions as a sensitizing configuration for boosting the performance of the sensor. This paper opens up a new approach towards improving the sensing activity of a 2D material via a synergistic vacancy and interface engineering.

Room-temperature gas sensing of ZnO-based gas sensor: A review

Abstract: Novel gas sensors with high sensing properties, simultaneously operating at room temperature are considerably more attractive owing to their low power consumption, high security and long-term stability. Till date, zinc oxide (ZnO) as semiconducting metal oxide is considered as the promising resistive-type gas sensing material, but elevated operating temperature becomes the bottleneck of its extensive applications in the field of real-time gas monitoring, especially in flammable and explosive gas atmosphere. In this respect, worldwide efforts have been devoted to reducing the operating temperature by means of multiple methods In this communication, room-temperature gas sensing properties of ZnO based gas sensors are comprehensively reviewed. Much more attention is particularly paid to the effective strategies that create room-temperature gas sensing of ZnO based gas sensors, mainly including surface modification, additive doping and light activation. Finally, some perspectives for future investigation on room-temperature gas-sensing materials are discussed as well.

Advances in designs and mechanisms of semiconducting metal oxide nanostructures for high-precision gas sensors operated at room temperature

Abstract: High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (e.g. nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.

Recent Progress in Solar-Blind Deep-Ultraviolet Photodetectors Based on Inorganic Ultrawide Bandgap Semiconductors

Abstract: Due to its significant applications in many relevant fields, light detection in the solar-blind deep-ultraviolet (DUV) wavelength region is a subject of great interest for both scientific and industrial communities. The rapid advances in preparing high-quality ultrawide-bandgap (UWBG) semiconductors have enabled the realization of various high-performance DUV photodetectors (DUVPDs) with different geometries, which provide an avenue for circumventing numerous disadvantages in traditional DUV detectors. This article presents a comprehensive review of the applications of inorganic UWBG semiconductors for solar-blind DUV light detection in the past several decades. Different kinds of DUVPDs, which are based on varied UWBG semiconductors including Ga2O3, MgxZn1−xO, III-nitride compounds (AlxGa1−xN/AlN and BN), diamond, etc., and operate on different working principles, are introduced and discussed systematically. Some emerging techniques to optimize device performance are addressed as well. Finally, the existing techniques are summarized and future challenges are proposed in order to shed light on development in this critical research field.

β-Ga2O3 for wide-bandgap electronics and optoelectronics

Abstract: β-Ga2O3 is an emerging, ultra-wide bandgap (energy gap of 4.85 eV) transparent semiconducting oxide (TSO), which attracted recently much scientific and technological attention. Unique properties of that compound combined with its advanced development in growth and characterization place β-Ga2O3 in the frontline of future applications in electronics (Schottky barrier diodes, field-effect transistors), optoelectronics (solar- and visible-blind photodetectors, flame detectors, light emitting diodes), and sensing systems (gas sensors, nuclear radiation detectors). A capability of growing large bulk single crystals directly from the melt and epi-layers by a diversity of epitaxial techniques, as well as explored material properties and underlying physics, define a solid background for a device fabrication, which, indeed, has been boosted in recent years. This required, however, enormous efforts in different areas of science and technology that constitutes a chain linking together engineering, metrology and theory. The present review includes material preparation (bulk crystals, epi-layers, surfaces), an exploration of optical, electrical, thermal and mechanical properties, as well as device design / fabrication with resulted functionality suitable for different fields of applications. The review summarizes all of these aspects of β-Ga2O3 at the research level that spans from the material preparation through characterization to final devices.