Arijeet Das

Effect of Si doping on electrical and optical properties of ZnO thin films grown by sequential pulsed laser deposition

The sequential pulsed laser deposition technique was used to grow highly transparent and c-axis oriented thin films of Si doped ZnO on sapphire substrates. On doping with Si, the resistivity of the virgin ZnO thin films was found to decrease from ~3.0 ? 10?2 to 6.2 ? 10?4???cm and its bandgap increased from about 3.28 to 3.44?eV at different doping concentrations. XPES measurements revealed that Si predominantly occupies the Zn lattice sites in the Si+3 state. The increase in the bandgap of the ZnO films with increasing Si concentration was found to be due to the collective effects of high carrier concentration induced Burstein?Moss blue shift and bandgap narrowing. Efficient photoluminescence (PL) was observed at room temperature from these Si doped ZnO films. The bandgaps obtained from the PL measurements were found to be Stokes shifted as compared with those obtained from the transmission spectra. Si doping of ZnO offers the possibility of developing superior transparent conducting electrodes for applications such as in display panels, solar cells and transparent resistive non-volatile memories.

Structural, electronic structure, and band alignment properties at epitaxial NiO/Al2O3 heterojunction evaluated from synchrotron based X-ray techniques

The valence band offset value of 2.3 ± 0.2 eV at epitaxial NiO/Al2O3 heterojunction is determined from photoelectron spectroscopy experiments. Pulsed laser deposited thin film of NiO on Al2O3 substrate is epitaxially grown along [111] direction with two domain structures, which are in-plane rotated by 60° with respect to each other. Observation of Pendellosung oscillations around Bragg peak confirms high interfacial and crystalline quality of NiO layer deposited on Al2O3 substrate. Surface related feature in Ni 2p3/2 core level spectra along with oxygen K-edge soft X-ray absorption spectroscopy results indicates that the initial growth of NiO on Al2O3 substrate is in the form of islands, which merge to form NiO layer for the larger coverage. The value of conduction band offset is also evaluated from the measured values of band gaps of NiO and Al2O3 layers. A type-I band alignment at NiO and Al2O3 heterojunction is also obtained. The determined values of band offsets can be useful in heterojunction based l...

Fine structures in refractive index of sapphire at the L II,III absorption edge of aluminum determined by soft x-ray resonant reflectivity

The optical constants of sapphire crystal (α-Al(2)O(3)) and amorphous Al(2)O(3) in the soft x-ray region (67-85 eV) around the aluminum LII,III absorption edge (73.1 eV) are determined by angle-dependent x-ray reflectivity. The differences between the optical constant values of both the samples are discussed. The fine structures obtained in the absorption of crystalline sapphire are explained. An absorption feature at 70.2 eV is observed for the first time for crystalline alumina. Both datasets are compared to the tabulated values of Henke et al. [At. Data Nucl. Data Tables 54, 181 (1993)], Weaver et al. [Physik Daten, Physics Data: Optical Properties of Metals (Fach-information zentrum, 1981), Vols. 18-1 and 18-2], and [Handbook of Optical Constants of Solids II (Academic, 1991)].

Effect of oxygen ion beam bombardment on depth resolved hydrogen distribution in stoichiometric alumina thin films, deposited by e-beam evaporation

Effect of oxygen ion beam bombardment on the hydrogen impurity distribution (as a function of depth) in alumina thin films is discussed. It is shown that the bombardment of oxygen ion beam during electron beam evaporation significantly decreases the hydrogen content in the films. The observed peak of hydrogen distribution at the silica alumina interface is explained on the basis of morphological changes happening to the silica alumina interface due to the oxygen ion beam bombardment. It is also shown that stoichiometry of these films, irrespective of the oxygen ion beam energy, remains same as that of sapphire crystal.

Data-reduction procedure for correction of geometric factors in the analysis of specular X-ray reflectivity of small samples

For small samples, the modification of the XRR profile by the geometrical factors manifesting due to profile and size of the beam and the size of the sample is significant. Geometrical factors extend till spill over angle which is often greater than critical angle for small samples. To separate the geometrical factor, it is necessary to know the spill over angle. Since geometrical factor is a smoothly varying function and extends beyond critical angle, it is impossible to determine the spill over angle from XRR profile of small samples. We have shown by comparing the normal XRR profile of a small sample with the XRR profile taken with a surface contact knife edge on the same sample, that the spill over angle can be determined. Thus we have developed a procedure for data reduction for small samples and validated it with suitable experiments. Unlike hitherto used methods which have drawbacks, this is a self consistent method for data reduction

Hydrogen removal from e-beam deposited alumina thin films by oxygen ion beam

Hydrogen interstitials and oxygen vacancies defects create energy levels in the band gap of alumina. This limits the application of alumina as a high-k dielectric. A low thermal budget method for removal of hydrogen from alumina is discussed. It is shown that bombardment of alumina films with low energy oxygen ion beam during electron beam evaporation deposition decreases the hydrogen concentration in the film significantly.

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.

Facile Synthesis and Characterization of β-Ga[sub 2]O[sub 3] Nanostructures 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.

Investigation of the Influence of Buffer Layer on the Interface Roughness of NbC/Si Multilayer

The influence of buffer layer on interface roughness has been investigated. With Si buffer layer, NbC/Si multilayer mirrors show 28% increase of reflectivity at 1st Bragg peak for 1.54A0. Reduction in physical and chemical roughness in the multilayer with buffer layer was calculated by fitting both specular and diffused scattering data.

Facile Synthesis and Characterization of β‐Ga2O3 Nanostructures 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.