A. Sudha

Bio: A. Sudha is an academic researcher from Indian Institute of Technology Kharagpur. The author has contributed to research in topics: Thin film & Materials science. The author has an hindex of 5, co-authored 7 publications receiving 70 citations.

Effects of annealing temperature on structural and electrical properties of indium oxide thin films prepared by thermal evaporation

Abstract: The effects of annealing temperature on the structural and electrical properties of indium oxide thin films of thickness 600 nm, prepared on glass substrate by thermal evaporation in vacuum, were investigated. The deposited films were annealed at 350 °C, 450 °C and 550 °C for 1 h. The structural and morphological properties of the films were investigated at different annealing temperatures by X-ray diffraction and scanning electron microscopy. The XRD patterns indicated amorphous structure of as-deposited films and annealed films had a preferred orientation along (222) plane and the crystallinity along with the grain size were augmented with annealing temperature. The SEM investigation showed that the grain size increased with annealing temperature. The behavior of electrical conductivity of the as-deposited and annealed films were determined by I − V measurement. The results exhibit the linear dependency with annealing temperature.

Effects of gamma irradiations on structural and electrical properties of indium oxide thin films prepared by thermal evaporation

Abstract: Effects of gamma irradiations on structural and electrical properties of the post-annealed indium oxide thin films of thickness 750 nm, prepared by thermal evaporation in vacuum, were studied. The thin films, exposed to various levels of the gamma radiation dose, were characterized by XRD, SEM and I – V measurements. Results show that the average grain size and the degree of crystallinity increase with the gamma radiation dose up to a certain dose and decrease thereafter. Results also show that the conductivity increases with the gamma radiation dose up to the same value of the dose and decreases thereafter. The dislocation density, however, shows the opposite trend of the dose dependence.

Achieving sensitive and stable indium oxide thin films for gamma radiation monitoring

Abstract: Indium oxide thin films of thickness 600 nm prepared by thermal evaporation in vacuum were annealed at different temperatures from 350 to 550 °C. The impact of the post-deposition thermal annealing on the structural evolution of the films, including the growth of grains, was investigated by XRD and SEM. The annealed films were also evaluated by X-ray photoelectron and photoluminescence spectroscopy. The gamma radiation dose dependences of the optical energy band gap for the as-deposited and annealed thin films were investigated using transmittance measurements. The band gap decreases with increase of dose for the as-deposited and thermally treated films up to certain level and then increases. Coplanar devices were fabricated using the as-deposited films and films annealed at different temperatures. After exposing them to different gamma radiation doses, DC conductivity measurements were carried out. The gamma radiation sensing property of the indium oxide thin films annealed at 400 °C exhibits the highest sensitivity in comparison to the as-deposited films and films annealed at other temperatures. The annealing at temperatures higher or lower than 400 °C causes an increase of electrical resistivity and decrease in sensitivity of the films. Also, the stability of the sensor devices was studied for about 8 months. The results showed that the sensors made of the as-deposited films were stable for about 2 months and lost about 52% of their sensitivity in about 8 months whereas the sensors made out of the films annealed at 400 °C were stable for about 4 months and lost about 26% of their sensitivity in about 8 months. This study presents a key idea of using the post-deposition thermal annealing to achieve highly sensitive and stable In2O3 film as gamma radiation sensor.

Gamma irradiation effect on the optical properties of tellurium dioxide films

Abstract: The gamma radiation induced optical properties of the tellurium dioxide films of thickness 1500 nm, deposited by thermal evaporation in the vacuum, were investigated. The dose dependences of the band gap and other optical parameters have been quantified from the transmittance spectra. The optical band gap decreases with the gamma radiation dose up to 400 Gy from 3.98 to 3.55 eV and increases beyond 400 Gy. Also, the refractive index and extinction coefficient increase appreciably with the gamma radiation dose up to 400 Gy and the two decrease beyond 400 Gy. This behavior of the optical properties is due to generation of the electronic localized states in the band gap and Urbach tail. The change in each of the optical properties due to gamma radiation can be an attractive idea for the TeO2 film as photo-sensitive film-based dosimeter. The proposed material as dosimeter has minimum detectable effect on a dose range of 400 Gy, which is best suited for possible industrial applications such as food processing and sterilization.

Study of structural, optical and electrical properties of gamma irradiated In2O3 thin films for device applications

Abstract: The influence of gamma irradiation on the structural, optical and electrical properties of indium oxide ( $$\hbox {In}_2\hbox {O}_3$$ ) thin films prepared by thermal evaporation has been reported. The X-ray diffraction analysis revealed that the gamma irradiated films up to a dose of 75 Gy exhibit better crystallinity, with a strong increase in the intensity of peak related to (222) plane of the cubic indium oxide structure. Further increase of the gamma dose results in the reduction of crystallinity and grain size. However, the dislocation density and micro strain show the reverse trend of the dose dependence. The transmittance of the films decreases with the gamma dose up to the same level, resulting in a decrease of bandgap from 3.65 to 3.30 eV. The increase of the band gap at higher doses might be due to increased structural disorder and more defect creation than annihilation. The I–V characteristics measured after each exposed dose showed a decrement in the resistance with the rise in radiation dose up to the same level and exceeding this level leads to damage of the device. This study also suggests that the gamma irradiation can be considered as a tool for the enhancement of the device properties amongst the other applications.

Indium oxide: A transparent, conducting ferromagnetic semiconductor for spintronic applications

Abstract: The optical and electrical properties are the two important dimensions of Indium oxide and its derivatives (indium tin oxide) and were well studied to understand the origin of wide electronic band gap and high electrical conductivity at room temperature. In 2 O 3 and its derivatives find many applications in electronic and optoelectronic domains based on the above properties. The recent discovery of ferromagnetism in In 2 O 3 at room temperature become a third dimension and lead to intensive research on enhancement of ferromagnetic strength by various means such as dopants and synthesis protocols and extrinsic parameters. The research lead to enormous experimental data and theoretical models proliferation over the past one decade with diverse insights into the origin of ferromagnetism in In 2 O 3 based dilute magnetic semiconductors. The experimental data and theoretical models of ferromagnetism in In 2 O 3 has been thoroughly surveyed in the literature and compiled all the data and presented for easy of understanding in this review. We have identified best chemical composition, geometry and synthesis protocols for strongest ferromagnetic strength and suitable theoretical model of magnetism has been presented in this review.

Antimony sulphide, an absorber layer for solar cell application

Abstract: Replacement of the toxic, expensive and scarce materials with nontoxic, cheap and earth-abundant one, in solar cell absorber layer, is immensely needed to realize the vision of green and sustainable energy. Two-micrometre-thin antimony sulphide film is considered to be adequate as an absorbing layer in solar cell applications. In this paper, we synthesize antimony sulphide thin films on glass substrate by physical vapour deposition technique, and the obtained films were then annealed at different temperatures (150–250 °C). The as-deposited and annealed samples were investigated for structural and optoelectronic properties using different characterization techniques. The X-ray diffraction analysis showed that the annealed samples were polycrystalline with Sb2S3 phase, while the as-deposited sample was amorphous in nature. The optical properties are measured via optical ellipsometric techniques. The measured absorbance of the film is adequately high, and every photon is found to be absorbed in visible and NIR range. The conductivity type of the films measured by hot-point probe technique is determined to be p-type. The optical band gap of the resulted samples was in the range (2.4–1.3 eV) for the as-deposited and annealed films.

An investigation of 60Co gamma radiation-induced effects on the properties of nanostructured α-MoO3 for the application in optoelectronic and photonic devices

Abstract: Gamma ray has sufficient energy to ionize and displace of atoms when interacts with optoelectronic and photonic devices that are placed at γ-radiation exposure environment, can be exposed to gamma radiation, resulting the alteration of the physical properties and hence the performances of devices. A comprehensive investigation of physical properties of the semiconductor materials under the influence of gamma radiation is essential for the effective design of devices for the application in the radiation exposure environment. In this article, a potential candidate for optoelectronic and photonic devices, orthorhombic MoO3 nanoparticles with average crystallite size of 135.31 nm successfully synthesized by hydrothermal method. Then, the properties of nanoparticles exposed to low (10 kGy) and high (120 kGy) absorbed dose of γ-rays from 60Co source were characterized by XRD, FESEM, FTIR and UV–Vis–NIR spectrophotometer and effects of absorbed doses was investigated for the first time. A significant change is observed in different physical properties of α-MoO3 nanoparticles after gamma exposure. The XRD patterns reveal the average crystallite size, intensity and the degree of crystallinity decrease for low dose (10 kGy) and increases for high dose (120 kGy). The calculated average crystallite size exposed to low and high doses are 127.79 nm and 136 nm, respectively. The lattice strain and dislocation density, however, shows the opposite trend of crystallite size with absorbed doses. This result is good evidence for the deterioration of crystallinity for low dose and improvement for high dose. The FESEM results reveal the significant effects of gamma doses on the micrographs of layered structure and on grain size. The optical studies disclose that band gap increases gradually from 2.78 to 2.90 eV, this behavior is associated with the reduction of electronic localized states. These results suggest that α-MoO3 nanoparticles could tolerate high doses of gamma radiation, making it a promising candidate for optoelectronic and photonic devices for γ-ray exposure environment applications.

Suitability of binary oxides for molecular-beam epitaxy source materials: A comprehensive thermodynamic analysis

Abstract: We have conducted a comprehensive thermodynamic analysis of the volatility of 128 binary oxides to evaluate their suitability as source materials for oxide molecular-beam epitaxy (MBE). 16 solid or liquid oxides are identified that evaporate nearly congruently from stable oxide sources to gas species: As2O3, B2O3, BaO, MoO3, OsO4, P2O5, PbO, PuO2, Rb2O, Re2O7, Sb2O3, SeO2, SnO, ThO2, Tl2O, and WO3. An additional 24 oxides could provide molecular beams with dominant gas species of CeO, Cs2O, DyO, ErO, Ga2O, GdO, GeO, HfO, HoO, In2O, LaO, LuO, NdO, PmO, PrO, PuO, ScO, SiO, SmO, TbO, Te2O2, U2O6, VO2, and YO2. The present findings are in close accord with available experimental results in the literature. For example, As2O3, B2O3, BaO, MoO3, PbO, Sb2O3, and WO3 are the only oxides in the ideal category that have been used in MBE. The remaining oxides deemed ideal for MBE awaiting experimental verification. We also consider two-phase mixtures as a route to achieve the desired congruent evaporation characteristic of an ideal MBE source. These include (Ga2O3 + Ga) to produce a molecular beam of Ga2O(g), (GeO2 + Ge) to produce GeO(g), (SiO2 + Si) to produce SiO(g), (SnO2 + Sn) to produce SnO(g), etc.; these suboxide sources enable suboxide MBE. Our analysis provides the vapor pressures of the gas species over the condensed phases of 128 binary oxides, which may be either solid or liquid depending on the melting temperature.

Effects of gamma irradiations on structural and electrical properties of indium oxide thin films prepared by thermal evaporation

Abstract: Effects of gamma irradiations on structural and electrical properties of the post-annealed indium oxide thin films of thickness 750 nm, prepared by thermal evaporation in vacuum, were studied. The thin films, exposed to various levels of the gamma radiation dose, were characterized by XRD, SEM and I – V measurements. Results show that the average grain size and the degree of crystallinity increase with the gamma radiation dose up to a certain dose and decrease thereafter. Results also show that the conductivity increases with the gamma radiation dose up to the same value of the dose and decreases thereafter. The dislocation density, however, shows the opposite trend of the dose dependence.