H₂, H₂S gas sensing properties of rGO/GaN nanorods at room temperature: Effect of UV illumination

Reddeppa, Maddaka,Park, Byung-Guon,Kim, Moon-Deock,Peta, Koteswara Rao,Chinh, Nguyen Duc,Kim, Dojin,Kim, Song-Gang,Murali, G. Elsevier 2018 Sensors and actuators. B, Chemical Vol.264 No.-

<P><B>Abstract</B></P> <P>In this work, reduced graphene oxide (rGO)/GaN nanorods (NRs) hybrid structure based sensors for hydrogen (H<SUB>2</SUB>) and hydrogen sulfide (H<SUB>2</SUB>S) gases has been demonstrated at room temperature. The morphological, elemental, and structural analyses were carried out by using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The electrical characterization of rGO/GaN NRs hybrid structures showed good rectifying behavior compared to pristine GaN NRs. The H<SUB>2</SUB> and H<SUB>2</SUB>S gas sensing measurements at different gas concentrations revealed that the rGO/GaN NRs exhibit superior sensing properties compared to pristine GaN NRs. In order to find the gas sensing mechanism of rGO/GaN NRs, hybrid structure sensor is also tested with NO<SUB>x</SUB> gas. Our experimental results revealed that the rGO/GaN NRs are good candidates for selective detection of H<SUB>2</SUB>S gas. The rGO/GaN NRs showed remarkably improved response under ultra-violet (λ = 365 nm) illumination, the photogenerated carriers could be responsible for increasing response of the gas sensor at 30 °C under UV illumination. In addition, humidity test of the rGO/GaN NRs sensor was also conducted in this work. Our experimental results suggested that decorating GaN NRs with solution-processable rGO is one of the effective ways to enhance the response of GaN nanostructures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The 2-dimentional rGO layer spin coated on the GaN NRs and used for improving the gas sensing properties. </LI> <LI> The rGO/GaN NRs showed higher response to the H<SUB>2</SUB> and H<SUB>2</SUB>S gases compared to pristine GaN NRs. </LI> <LI> UV illumination enhances the response of rGO/GaN NRs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A novel low-temperature resistive NO gas sensor based on InGaN/GaN multi-quantum well-embedded p-i-n GaN nanorods

Reddeppa, Maddaka,Park, Byung-Guon,Chinh, Nguyen Duc,Kim, Dojin,Oh, Jae-Eung,Kim, Tae Geun,Kim, Moon-Deock The Royal Society of Chemistry 2019 Dalton Transactions Vol.48 No.4

<P>In gas sensors, metal oxide semiconductors have been considered as favorable resistive-type toxic gas sensing materials. However, the higher temperature operation of metal oxides becomes a barrier for their wide range of applications in explosive and flammable gas environments. In this regard, great efforts have been devoted to reducing the operating temperature of the sensor. We demonstrated a chemical resistor-type NO gas sensor based on p-i-n GaN nanorods (NRs) consisting of InGaN/GaN multi-quantum wells (MQW). The sensor exhibited superior NO gas sensing performance to p-type GaN NRs. Furthermore, it also showed a remarkably improved response and fast recovery under UV irradiation (<I>λ</I> = 367 nm) of different UV intensities (7 to 20 mw cm<SUP>−2</SUP>) under reverse bias. The sensing performance of MQW-embedded p-i-n GaN NRs was enhanced with the boosted response by 4-fold at 35 °C under UV irradiation. The significant decrease in the resistance of the sensor under UV irradiation was mainly due to the extraction of photo-generated carriers under reverse bias, which can enhance the ionization of oxygen molecules. In addition, the effect of relative humidity (30%-60%) on the gas sensing performance was also manifested in this study. The selectivity of the sensor was determined by using other gases (NO, NO2, O2, NH3, H2S, CO, and H2), which exhibited a low response towards all tested gases other than NO. The experimental results demonstrated that p-i-n GaN NRs with InGaN/GaN MQW is a promising material for the detection of NO gas. Specific emphasis was laid on the enhanced response of p-i-n GaN NRs in reverse bias under UV irradiation.</P>

Improved Schottky behavior of GaN nanorods using hydrogen plasma treatment

Reddeppa, Maddaka,Park, Byung-Guon,Lee, Sang-Tae,Hai, Nguyen Hoang,Kim, Moon-Deock,Oh, Jae-Eung ELSEVIER 2017 CURRENT APPLIED PHYSICS Vol.17 No.2

<P>In order to find the effect of hydrogen (H) treatment on leakage current and current conduction mechanism in GaN nanorods (NRs) Schottky diode, GaN NRs surface was subjected to H plasma treatment. Experimental results showed that Schottky barrier height (Phi(b))increased, while the ideality factor (n) decreases by the H treatment. The Phi(b), n of as-grown GaN NRs were found to be 0.54 eV, 2.16, on the other hand in H treated GaN NRs Schottky diodes, Phi(b) was found to be increase to 0.72 eV, and n decreased to 1.30. Barrier inhomogeneity was confirmed by temperature dependence I-V parameters. The surface state density (N-SS) calculated from Terman's method were found to be 1.21 x 10(13) eV(-1)cm(-2) and 2.15 x 10(12) eV(-1)cm(-2) for as-grown and H treated GaN NRs respectively. These results suggested H treatment effectively passivate the surface states and decreased N-SS could be leads to enhancement in the Schottky behavior of GaN NRs. (C) 2016 Elsevier B.V. All rights reserved.</P>

DNA-CTMA functionalized GaN surfaces for NO₂ gas sensor at room temperature under UV illumination

Reddeppa, Maddaka,Mitta, Sekhar Babu,Park, Byung-Guon,Kim, Song-Gang,Park, Sung Ha,Kim, Moon-Deock Elsevier 2019 ORGANIC ELECTRONICS Vol.65 No.-

<P><B>Abstract</B></P> <P>Considering the power consumption and safety risks in the presence of combustible gases, sensor operation at room temperature (RT∼28 °C) has drawn much interest in recent days. Different strategies have been found to meet the effective sensor performance at RT. Here, we report a riveting combination of DNA‒CTMA/GaN (DGaN) hybrid structure for high-sensitive NO<SUB>2</SUB> gas sensor at RT. The surface modifications are caused by the functional groups of DNA‒CTMA interactions with GaN. The XPS studies reveal that the native oxides of GaN surface are binding with the functional groups of DNA‒CTMA. The DGaN hybrid structure display higher response to various concentrations (100–10 ppm) of NO<SUB>2</SUB> compared to the pristine GaN film. The effect of UV illumination on NO<SUB>2</SUB> gas sensing performance of DGaN is also manifested, and the response of the sensor is enhanced under UV illumination in comparison with those of dark condition. From our observations, the amine groups and the negatively charged hydroxyl groups in DNA‒CTMA helps for the higher response of gas sensor by the hybrid structure which makes them a good candidate for high-response NO<SUB>2</SUB> gas sensors at RT.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel DNA-CTMA/GaN structure for NO<SUB>2</SUB> gas sensor. </LI> <LI> DNA-CTMA/GaN hybrid structure working at room temperature. </LI> <LI> The response of sensor is superior under UV illumination. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Ferromagnetic properties of GaN nanorods: Effect of silicon doping and hydrogenation

Maddaka Reddeppa,Byung-Guon Park,Sang-Tae Lee,Moon-Deock Kim,Rambabu Kuchi,Jong-Ryul Jeong 한국물리학회 2016 Current Applied Physics Vol.16 No.8

In this paper, we have investigated effect of Si doping and hydrogenation on room temperature ferromagnetism in GaN nanorods (NRs) grown on patterned Si (111) substrate by plasma assisted molecular beam epitaxy. Vibrating sample magnetometer measurements revealed that ferromagnetic properties enhanced with increased in Si concentration and maximum saturation of magnetization was about 0.023emu/g, which is three times higher than that of undoped GaN NRs. Hydrogenation of Si doped GaN NRs strongly suppresses the ferromagnetic behavior, while thermal annealing of hydrogenated GaN NRs revealed that recovery of ferromagnetic properties. Hydrogen compensates the free electron concentration in Si doped GaN NRs which tends to decrease ferromagnetic properties and recovery of ferromagnetic properties due to thermal dissociation of hydrogen atoms from GaN NRs. These results suggest that ferromagnetic properties enhanced in Si doped GaN NRs, which is possibly related to increase in free electron concentration.

p-Pheneylendiamine functionalized rGO/Si heterostructure Schottky junction for UV photodetectors

Chandrakalavathi, T.,Reddeppa, Maddaka,Revathi, T.,Basivi, Praveen Kumar,Viswanath, Sujaya Kumar,Murali, G.,Kim, Moon-Deock,Jeyalakshmi, R. Elsevier 2019 Diamond and related materials Vol.93 No.-

<P><B>Abstract</B></P> <P>In this work, we report on p-Phenylenediamine (PPD) functionalized reduced graphene oxide (rGO)/Si hybrid-structure designed for UV photodetector applications (PD). The hybrid-structure was characterized by using Fourier Transform-infrared spectroscopy, X-ray photoelectron spectroscopy to confirm the formation of nano-hybrid structure and the experimental results confirmed the covalent bond between rGO and PPD. The diode parameters such as barrier height, series resistance, and ideality factor were estimated for both PPD functionalized rGO (PrGO)/Si and rGO/Si heterostructure by using I-V characteristics. The time-resolved photocurrent spectroscopy used to examine the photoresponse properties of both PrGO/Si and rGO/Si samples with UV light (λ = 382 nm). The experimental results showed that PrGO/Si exhibited significant UV photoresponse than that of rGO/Si PD. The PrGO/Si heterostructure device exhibited photoresponsivity of 1.4 × 10<SUP>−3</SUP> A/W, which is 15 times higher than rGO/Si. The high photoresponse was attributed to the synergistic effects originated from the charge transfer between PPD and rGO. The results proved that PrGO is a promising material for high response photodetector applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> p-Pheneylendiamine covalently functionalized with rGO. </LI> <LI> PPD-rGO/Si hybrid structure practically applied for photodetector applications. </LI> <LI> The charge transfer between PPD and rGO could be enhanced the photoresponse of hybrid structure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

High performance UV photodetectors using Nd³⁺ and Er³⁺ single- and co-doped DNA thin films

Vellampatti, Srivithya,Reddeppa, Maddaka,Dugasani, Sreekantha Reddy,Mitta, Sekhar Babu,Gnapareddy, Bramaramba,Kim, Moon-Deock,Park, Sung Ha Elsevier 2019 Biosensors & bioelectronics Vol.126 No.-

<P><B>Abstract</B></P> <P>Even though lanthanide ion (Ln<SUP>3+</SUP>)-doped DNA nanostructures have been utilized in various applications, they are rarely employed for photovoltage generating devices because of difficulties in designing DNA-based devices that generate voltages under light illumination. Here, we constructed DNA lattices made of synthetic strands and DNA thin films extracted from salmon (SDNA) with single-doping of Nd<SUP>3+</SUP> or Er<SUP>3+</SUP> and co-doping of Nd<SUP>3+</SUP>/Er<SUP>3+</SUP> for high performance UV detection. The topological change of the DNA double-crossover (DX) lattices during the course of annealing was estimated from atomic force microscope (AFM) images to find the optimum concentration of Ln<SUP>3+</SUP> ([Ln<SUP>3+</SUP>]<SUB>O</SUB>). No topological disturbance in DNA DX lattices were observed up to [Ln<SUP>3+</SUP>]<SUB>O</SUB>, and significant enhancement in the physical properties was obtained at [Ln<SUP>3+</SUP>]<SUB>O</SUB>. The interactions between Ln<SUP>3+</SUP> and SDNA were examined using spectroscopic methods of UV–visible, Raman, and X-ray photoelectron spectroscopy (XPS). Current and photovoltage measurements for Ln<SUP>3+</SUP>-doped SDNA thin films under UV illumination with varying power intensities were conducted. Under UV illumination, the photocurrent and photovoltage of Ln<SUP>3+</SUP>-doped SDNA thin films increased with increasing applied external voltages and input power intensities, respectively. In addition, we observed considerable increases in photovoltage responses, <I>i.e.</I>, 5-fold increase for Nd<SUP>3+</SUP>, 10-fold for Er<SUP>3+</SUP>, and 13-fold for Nd<SUP>3+</SUP>/ Er<SUP>3+</SUP>, compared to the pristine SDNA due to the additional charge carriers generated in Ln<SUP>3+</SUP>-doped SDNA thin films. Device performance was measured in terms of photovoltage responsivity and retention characteristics. These phenomena indicate the high stability and substantial endurance characteristics of Ln<SUP>3+</SUP>-doped SDNA thin films.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ln<SUP>3+</SUP>-doped DNA thin films are rarely employed for photovoltage generating devices yet. </LI> <LI> We constructed DNA thin films with doping of Nd<SUP>3+</SUP> and Er<SUP>3+</SUP> for high performance UV detection. </LI> <LI> The interactions between Ln<SUP>3+</SUP> and DNA were examined using spectroscopic methods of UV–visible, Raman, and XPS. </LI> <LI> Under UV, the photocurrent and photovoltage of Ln<SUP>3+</SUP>-doped DNA thin films were varied with voltage and power, respectively. </LI> <LI> Ln<SUP>3+</SUP>-doped DNA thin films exhibited high stability and substantial endurance characteristics. </LI> </UL> </P>

Gold nanoparticle-embedded DNA thin films for ultraviolet photodetectors

Mitta, Sekhar Babu,Reddeppa, Maddaka,Vellampatti, Srivithya,Dugasani, Sreekantha Reddy,Yoo, Sanghyun,Lee, Seungwoo,Kim, Moon-Deock,Ha Park, Sung Elsevier 2018 Sensors and actuators. B Chemical Vol.275 No.-

<P><B>Abstract</B></P> <P>Although DNA (low-cost, highly transparent, low optical loss, biodegradable, non-toxic, and highly flexible) and gold nanoparticles (Au NPs, exhibiting interband transition and localized surface plasmon resonance) have been intensively studied, DNA with Au NPs in photodetectors is rarely discussed. Here, we constructed salmon DNA (SDNA) thin films and incorporated Au NPs to demonstrate efficient and high-performance UV photodetectors. The Au NP-embedded SDNA thin films were characterized with UV–vis absorption, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and conductivity measurements in order to understand their physical and chemical properties. The FTIR and XPS measurements elucidated how Au NPs become embedded in SDNA, through analysis of chemical binding and chemical composition. A current increase was observed under UV illumination when performing conductivity measurements. In addition, photovoltage measurements were conducted to investigate the significance of photoresponse and retention characteristics. The density of <I>d</I>-band electrons in Au NPs and the charge carriers in SDNA were observed to increase under UV illumination, followed by a significantly enhanced UV photoresponse. From our observations, the photovoltage displayed a flat response over time, which indicated their stability, durability, and high Au NP retention.</P> <P><B>Highlights</B></P> <P> <UL> <LI> DNA thin films incorporated with Au NPs are fabricated to demonstrate efficient and high-performance UV photodetectors. </LI> <LI> The Au NP-embedded SDNA thin films are characterized in order to understand their physical and chemical properties. </LI> <LI> The FTIR and XPS elucidate how Au NPs become embedded in SDNA,through analysis of chemical binding and chemical composition. </LI> <LI> Photovoltage measurements are conducted to investigate the significance of photoresponse and retention characteristics. </LI> <LI> Photovoltage response indicates the stability, durability, and high Au NP retention. </LI> </UL> </P>

Polypyrrole/GaN Nano rods based organic/inorganic hybrid heterojunction for high performance self-powered ultraviolet photodetectors

Kedhareswara Sairam Pasupuleti,Maddaka Reddeppa,Byung-Guon Park,Moon-Deock Kim,Song-Gang Kim,Jae-Eung Oh 한국진공학회 2020 한국진공학회 학술발표회초록집 Vol.2020 No.8

N-GQDs incorporated SnO₂ nanotubes by electrospinning for ammonia sensor with enhanced performance

( Chundi Seshendra Reddy ),( Maddaka Reddeppa ),권빈희,박성민,인인식 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

Pure and N-GQDs (Nitrogen doped graphene quantum dots) incorporated SnO₂ nanotubes (NTs) were fabricated by a one-step electrospinning method. The structure, morphology, chemical state and specific surface area were analyzed. The SnO₂ nanotubes consists of tens of thousands of SnO₂ nanoparticles with an ultra-small grain size. The as-synthesized pure and N-GQDs incorporated SnO₂ nanotubes were used to fabricate gas sensor. It was found that the gas response toward 100 ppm of ammonia was improved from 6.48 to 82.44 at room temperature, through the activation by N-GQDs. And the results indicate that the sensor based on N-GQDs incorporated SnO₂ not only has ultrahigh sensitivity but also possesses good response-recovery properties, linear dependence, repeatability, selectivity and long-term stability, demonstrating the potential to use N-GQDs incorporated SnO₂ nanotubes as ammonia gas sensors. ** 2019년 한국교통대학교 지원을 받아 수행하였음.