Ultra violet sensors based on nanostructured ZnO spheres in network of nanowires: a novel approach

The ZnO nanostructures consisting of micro spheres in a network of nano wires were synthesized by direct vapor phase method. X-ray Photoelectron Spectroscopy measurements were carried out to understand the chemical nature of the sample. ZnO nanostructures exhibited band edge luminescence at 383 nm. The nanostructure based ZnO thin films were used to fabricate UV sensors. The photoresponse measurements were carried out and the responsivity was measured to be 50 mA W−1. The rise and decay time measurements were also measured

Detection of surface states in GaAs and InP by thermally stimulated exoelectron emission spectroscopy

The energy distribution and relative densities of electronically active surface defects have been studied using thermally stimulated exoelectron emission (TSEE) spectroscopy. This novel and relatively simple technique has high sensitivity for detecting the surface states which are difficult to assess by other techniques. Here this technique is successfully used for detecting the pinned positions of the Fermi level in n-GaAs and n-InP which are, respectively, 0.91 and 0.43 eV below the conduction bands corresponding to 2Eg/3 and Eg/3 as expected. Antisite and oxygen related defects in these semiconductors are also identified at the surface. The relative TSEE peak intensities correlate very closely to the reported surface recombination velocities for these materials which are two to three orders of magnitude higher for GaAs. The effect of chromium on the surface states in these semiconductors, studied using semi-insulating GaAs, showed partial passivation of the surface defects in semi-insulating GaAs resulting in unpinning of the Fermi levels. Fe doped InP did not, however, show any sign of dopant induced deep levels

Ultrafast Laser Ablation and Deposition of Wide Band Gap Semiconductors

Isolated nanoparticles of the wide band gap II−VI semiconductors CdS and ZnS were produced by ultrafast pulsed laser deposition using pulses of ≈300 fs at two wavelengths of 527 and 263 nm. Upon repetitive target irradiation, the isolated nanoparticles assemble to form a nanostructured film whose structural and chemical properties are compared to those of the targets. UV ablation at 263 nm yields nanoparticles of 5 nm average diameter in the case of CdS. At this wavelength the crystalline phase and stoichiometry of the films markedly differ from those of the target. At 527 nm the average size of the nanoparticles is larger, about 13 nm, but the deposits keep the structural and chemical characteristics of the target. For ZnS the size of the nanoparticles is larger than for CdS although their properties also resemble those of the target when they are produced upon irradiation in the visible. The results obtained allow discussion of the interplay between the light absorption step, the plume dynamics, and the film growth and their impact on the structure and nanometer morphology of the deposited material, while at the same time they exemplify the possibility of their control through the choice of the wavelength of the femtosecond pulses