R. Jangir

Photoluminescence study of β-Ga2O3 nanostructures annealed in different environments

β-Ga2O3 nanostructures (nanowires, nanoribbons, and nanosheets) were synthesized via vapor transport method on gold coated silicon substrate in N2 ambient and these β-Ga2O3 nanostructures grown on silicon substrates were taken as the starting material to study the effect of annealing in the different environments (oxygen, water vapour, and ammonia solution) on the structural front and photoluminescence (PL) properties. The PL spectra of β-Ga2O3 nanostructures exhibit a UV-blue emission band whose intensity is strongly affected by the annealing in different environments. Annealing modifies the surface of the nanostructures by creating surface states which quench the PL by creating competitive nonradiative paths. This study also indicates the dominance of the formation of water induced surface states over ammonia induced surface states. The irreversible nature of these defects significantly affects the applicability of this system in moist high temperature environments.

Applicability of Langmuir equation to oxygen pressure dependent photoluminescence from β-Ga2O3 nanostructures

β-Ga2O3 nanostructures were synthesized via vapor transport method on gold coated Silicon substrate in N2 ambient. The as synthesized products were investigated by grazing incident X-ray diffraction, scanning electron microscopy and photoluminescence (PL) spectroscopy. It is shown that the intensity of photoluminescence from the ensemble of β-Ga2O3 nanostructures in oxygen gas ambience is correlated with the oxygen pressure through the Langmuir equation. This correlation is found to be reversible and reproducible. This phenomenon, which was not observed in the bulk β-Ga2O3 single crystal, is attributed to the oxygen related shallow trap surface states of the nanostructures with energies at about 4.2 eV above the valance band. Based on the changes in the PL intensity with the oxygen pressures, a possible mechanism for the observed photoluminescence is suggested. The present results provide a route for room-temperature response of oxygen in the gallium oxide nanostructures.

Study on structural and optical properties of α-(AlxCr1-x)2O3 (0 ≤ x ≤ 1) solid solutions

We report on structural and optical properties for ternary α-(AlxCr1-x)2O3 (0 ≤ x ≤ 1) solid solutions synthesized by using solid sate reaction method. Single R-3c phase was obtained for the Aluminum composition of 0 ≤ x ≤ 1. Due to difference in the ionic radia of Al3+ and Cr3+, in plane lattice parameter showed deviation from the vegard’s law. Optical absorption spectra for the solid solutions showed a blue shift of ∼ 0.5 eV in the optical gap. It has also been observed that Cr 3d level shifted towards the O 2p level in the valance band which indicates the enhancement of hybridization in the d and p levels, which is related to the delocalization of hole states, responsible for p-type conduction in wide band gap semiconductors. The results suggests that ternary α-(AlxCr1-x)2O3 (0 ≤ x ≤ 1) can be useful in the field of UV transparent electronics and UV photodetectors.We report on structural and optical properties for ternary α-(AlxCr1-x)2O3 (0 ≤ x ≤ 1) solid solutions synthesized by using solid sate reaction method. Single R-3c phase was obtained for the Aluminum composition of 0 ≤ x ≤ 1. Due to difference in the ionic radia of Al3+ and Cr3+, in plane lattice parameter showed deviation from the vegard’s law. Optical absorption spectra for the solid solutions showed a blue shift of ∼ 0.5 eV in the optical gap. It has also been observed that Cr 3d level shifted towards the O 2p level in the valance band which indicates the enhancement of hybridization in the d and p levels, which is related to the delocalization of hole states, responsible for p-type conduction in wide band gap semiconductors. The results suggests that ternary α-(AlxCr1-x)2O3 (0 ≤ x ≤ 1) can be useful in the field of UV transparent electronics and UV photodetectors.

Increase in depolarization temperature and improvement in ferroelectric properties by V5+ doping in lead-free 0.94(Na0.50Bi0.50)TiO3-0.06BaTiO3 ceramics

A detailed study was carried out to investigate the effects of poling on structure, vibrational, dielectric, and ferroelectric properties of donor-doped (V5+ at Ti4+-site) lead-free Na0.47Bi0.47Ba0.06Ti(1-x)VxO3, (x = 0, 0.01, and 0.03) ceramics fabricated via a modified sol-gel method. Rietveld refinement of synchrotron radiation source powder x-ray diffraction data showed that unpoled samples are in rhombohedral R3c phase whereas poled samples showed a mix rhombohedral R3c and tetragonal P4mm phases at ambient temperature, due to a long-range order established in lattice system after poling. V+5 doping increases the rhombohedral distortion in unpoled and poled samples while it reduces the tetragonality in poled samples. Vibrational study revealed that unpoled samples have more lattice disorder compared to poled samples. X-ray absorption near edge spectroscopy measurement confirmed that Ti and V are in 4+ and 5+ oxidation states, respectively, for all poled and unpoled samples. The average grain size was found to decrease from 5.6 ± 0.5 μm for x = 0 to 1.0 ± 0.2 μm for x = 0.03. Depolarization temperature was found to increase significantly in poled samples from ∼104 °C for undoped sample to 150 °C for the sample with 1% vanadium substitution. Drastic improvements in ferroelectric and dielectric properties are explained in terms of structural changes. High remnant polarization Pr ∼ 31.4 μC/cm2 and moderately low coercive field Ec ∼ 20 kV/cm have been observed at an applied electric field of ∼35 kV/cm for the sample with 1% vanadium substitution which makes it an attractive candidate for ferroelectric applications.A detailed study was carried out to investigate the effects of poling on structure, vibrational, dielectric, and ferroelectric properties of donor-doped (V5+ at Ti4+-site) lead-free Na0.47Bi0.47Ba0.06Ti(1-x)VxO3, (x = 0, 0.01, and 0.03) ceramics fabricated via a modified sol-gel method. Rietveld refinement of synchrotron radiation source powder x-ray diffraction data showed that unpoled samples are in rhombohedral R3c phase whereas poled samples showed a mix rhombohedral R3c and tetragonal P4mm phases at ambient temperature, due to a long-range order established in lattice system after poling. V+5 doping increases the rhombohedral distortion in unpoled and poled samples while it reduces the tetragonality in poled samples. Vibrational study revealed that unpoled samples have more lattice disorder compared to poled samples. X-ray absorption near edge spectroscopy measurement confirmed that Ti and V are in 4+ and 5+ oxidation states, respectively, for all poled and unpoled samples. The average grain size was...

Effect of growth parameters in controlling the growth direction of In2O3 micro/nanowires

In this study, effects of growth temperature and incoming reactant vapor concentration on the growth direction of In2O3 Micro/Nanowires have been studied. The study shows that the growth direction of the wires having same cross-section can be changed from to by changing the growth temperature. Change in the incoming reactant vapor concentration at the same growth temperature shows two phenomena. First, cross-section of the wires changed from micron to nanometers. Second, growth directions of the wires changed from to respectively. A possible mechanism for the observed results is discussed in term of surface/interface energy. The mechanism determining the growth direction of the In2O3 wires is presented.

Study of O2 sensitive photoluminescence of β-Ga2O3 nanostructures annealed in moist environments

In this study, effect of annealing in moist environment on the photoluminescence response to the oxygen (O2) is studied. β- Ga2O3 nanostructures were synthesized via vapor transport method on gold coated silicon substrate in N2 ambient. These β- Ga2O3 nanostructures were annealed in the different environment (water vapor and ammonia solution) and then room temperature PL measurements have been done at different oxygen partial pressures. PL results show that annealing modifies the surface of the nanostructures by creating permanent surface states which reduces the PL intensity response to the O2 because of competitive nonradiative paths. A possible mechanism for this behavior is also suggested.

Correlation between surface modification and photoluminescence properties of β-Ga2O3 nanostructures

In this work three different growth methods have been used to grow β-Ga2O3 nanostructures. The nanostructures were characterized by Grazing Incident X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and Photoluminescence Spectroscopy. Photoluminescence spectra for all the samples of β-Ga2O3 nanostructures exhibit an UV and blue emission band. The relative intensity of UV and blue luminescence is strongly affected by the surface defects present on the nanostructures. Our study shows that Photoluminescence intensity of UV and blue luminescence can be reliably used to determine the quality of β-Ga2O3 nanostructures. Further the work opens up the possibility of using UV excitation and subsequent Photoluminescence analysis as a possible means for oxygen sensing. The Photoluminescence mechanism in β-Ga2O3 nanostructures is also discussed.

Photoluminescence study of β−Ga2O3 nanostructures under different oxygen pressure conditions

β−Ga2O3 nanostructures including nanowires, nanoribbons and nanosheets were synthesized via vapor transport method on gold coated Silicon substrate in N2 ambient. The as synthesized products were investigated by Grazing Incident X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and photoluminescence. The PL spectra of β−Ga2O3 nanostructures exhibit a UV-blue emission band which is strongly affected by the oxygen pressure in terms of PL intensity. We believe that because of desorption of oxygen, surface of the nanostructures is reconstructed and this may create surface states which quench PL by creating competitive nonradiative paths. It provides an alternate route of oxygen sensing at room temperature and low pressure conditions. The luminescence mechanism, for this, is also discussed.

Study the effect of annealing in different environment on the optical properties of β- Ga2O3 nanostructures

β- Ga2O3 nanostructures including nanowires, nanoribbons and nanosheets were synthesized via vapor transport method on gold coated Silicon substrate in N2 ambient and these β- Ga2O3 nanostructures grown on silicon substrates were taken as the starting material to study the effect of annealing in the different environment (oxygen, water vapor and ammonia solution) on the structural front and photoluminescence properties. The PL spectra of β- Ga2O3 nanostructures exhibit a UV-blue emission band which is strongly affect by the annealing in different environment in terms of intensity. We believe that because of annealing, surface of the nanostructures is modified and this may create surface states which quench PL by creating competitive nonradiative paths.

Facile Synthesis and Characterization of β‐Ga2O3Nanostructures via Vapor Transport Method

β‐ Ga 2 O 3 nanostructures on a large scale were fabricated on the Silicon substrate via vapor transport method in nitrogen ambient. The growth was carried out in a tube furnace with Ga metal and Ga 2 O 3 powder serving as the source materials. The as synthesized products were characterized by GIXRD, SEM, HRTEM and room temperature photoluminescence. The diameter and length of β‐ Ga 2 O 3 nanowires ranges from 60–200 nm and 10–100 micron respectively. HRTEM observations suggested that the nanowires are single crystalline with interplaner distance of 0.47 nm. The PL spectrum of β‐ Ga 2 O 3 nanostructures exhibits a broad strong blue emission band centered at 450 nm. The possible growth and luminescence mechanism of β‐ Ga 2 O 3 nanostructures are also discussed.