R.G. Singh

Structural, Transport and Optical Properties of Boron-doped Zinc Oxide nanocrystalline

The paper has reported the structural, transport and optical properties of boron doped zinc oxide (ZnO:B) thin films grown on glass substrate by sol-gel spin coating process. It is observed from the analysis of the X-ray diffraction (XRD) results that the crystalline quality of the films is improved with increasing B concentration. A crystallite size of ∼17 nm is obtained for B doped films. A minimum resistivity of 7.9×l0 −4 Ω·cm is obtained at 0.6 at.% of B concentration in the ZnO:B films. Ionized and intragrain cluster scattering are found to dominate the scattering mechanism in ZnO:B films. Optical interference pattern in transmittance spectra shows good homogeneity with a transparency of ∼88% in the visible region. The band gap of the films is increased from 3.24 to 3.35 eV with increasing B concentration. Band gap widening is analyzed in terms of Burstein–Moss shift. The origin of the broad band photoluminescence (PL) spectra is explained in terms of the intragrain cluster scattering.

Electronic excitation induced mass transport on 200 MeV 107Ag+14 ion irradiated Si surface

Modification on Si (111) surface resulting from 200 MeV 107Ag+14 ion irradiation at an incidence angle of 15° with respect to the surface normal has been investigated by atomic force microscope (AFM) and x-ray diffraction techniques. Root mean square roughness measured using AFM was found to increase from 0.96 nm in the pristine sample to 18.33 nm in the sample irradiated with an ion fluence of 5×1013 ions/cm2. This spectacular increase in surface roughness is ascribed to the displacement of Si atoms driven by the creation of unsaturated dangling bonds on the Si surface during swift heavy ion irradiation. At a fluence of 5×1013 ions/cm2, a new type of ditch and dike structure was observed. These structures were distributed over the irradiated surface. Each ditch is followed by a dike. This is attributed to the cumulative effect of ion irradiation arising due to overlapping of ion-induced damaged zones and electronic excitation-induced shear motion of the atoms towards the surface.

Softening of phonons by lattice defects and structural strain in heavy ion irradiated nanocrystalline zinc oxide films

Origin of the Raman mode in nanocrystalline zinc oxide in the vicinity of A1 (LO) phonon mode induced by energetic heavy ions is reported. The evolution of this mode in the irradiated films is ascribed to the effect of disorder and the high density of lattice defects induced by irradiation. The presence of such defects is confirmed by the reduction in the intensity of E2 (high) mode and band bending of the near band edge absorption. A softening of the evolved Raman mode with increasing in ion fluence is also observed. This softening cannot be attributed to spatial confinement of phonons, as the sizes of the crystallites are large. Therefore, it is explained in terms of the combined effects of phonon localization by lattice defects and the structural strain in the lattice induced by electronic energy loss transferred by energetic heavy ions.

Temperature-dependent roughness of electronically excited InP surfaces

Topographical evolution of 100 MeV Au8+-ion-irradiated InP surfaces was studied using atomic-force microscopy (AFM). The surfaces were roughened under dense electronic excitations. Root-mean-square roughness measured from AFM studies showed an exponential saturation behavior with fluence. Sample temperature during irradiation was found as a parameter to control the amount of roughness on the surface and the evolution of irradiated surface topography is discussed in terms of thermal spike model.

Nanoscale defect formation on InP surface by swift gold ion impact

Abstract The atomic force microscopy (AFM) was used to image nanoscale defect on InP surface induced by 100 MeV Au8+ ions. These defects manifest themselves as pits or hillocks in AFM images depending on the scan direction. The nuclear energy loss (Sn) of swift heavy ion was found to be a decisive parameter for the creation of nanoscale defects, which otherwise supposed to be neglected at the surface for inelastic electronic energy loss (Se) dominant processes.

Carrier transport mechanism of highly-sensitive niobium doped titanium dioxide/p-Si heterojunction photodiode under illuminations by solar simulated light

Nano-crystalline Nb doped anatase TiO2 (NTO) thin film was deposited on p-type Si substrate for fabrication of n-NTO/p-Si heterojunction photodiode using RF magnetron sputtering technique. Rutherford backscattering spectrometry and Raman spectroscopy results suggest the substitutional incorporation of Nb5+ ions in anatase TiO2 lattice, which is evidenced from large stiffening of Eg(1) and softening of B1g Raman modes. The current density-voltage (J-V) characteristics are measured and important diode parameters of n-NTO/p-Si heterojunction diode are determined, such as ideality factor, barrier height, and series resistance. Diode exhibits excellent behavior under dark condition as rectification ratio is found to be ∼7 × 102 with high forward current density ∼1.54 A/cm2 at 5 V. The n-NTO/p-Si heterojunction works as an efficient photodiode in reverse bias under simulated solar light illumination with high contrast ratio ∼225 at −2 V and very high photo responsivity ∼2.7 A/W at −5 V. The high photo responsiv...

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

The effect of Niobiumdoping and size of crystallites on highly transparent nano-crystalline NiobiumdopedTitanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nbdoping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm−1 for the Eg(1) mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm−1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure(NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.

Multifunctional hybrid diode: Study of photoresponse, high responsivity, and charge injection mechanisms

A multifunctional hybrid heterojunction diode is developed on porous silicon and its current density-voltage characteristics reveal a good rectification ratio along with other superior parameters such as ideality factor, barrier height and series resistance. The diode also functions as an efficient photodiode to manifest high photosensitivity with high responsivity under illumination with broadband solar light, UV light, and green light. The diode is also carefully scrutinized for its sensitivity and repeatability over many cycles under UV and green light and is found to have a quick response and extremely fast recovery times. The notable responsivity is attributed to the generation of high density of excitons in the depletion region by the absorption of incident photons and their separation by an internal electric field besides an additional photocurrent due to the charging of polymer chains. The mechanisms of generation, injection and transport of charge carriers are explained by developing a schematic ...