Pulsed Laser Chemical Vapor Deposition Research Articles

Pulsed laser chemical vapor deposition of a mixture of W, WO2, and WO3 from W(CO)6 at atmospheric pressure

Pulsed laser irradiation at 355nm was used to deposit tungsten (W) films from tungsten hexacarbonyls (W(CO)6) on transparent glass substrates in air. The time dependence of W deposition revealed that the reaction proceeded via nucleation and growth; photolytic decomposition initiated W nuclei, which acted as laser absorbers and grew by direct deposition on the nuclei, driven mainly by a pyrolytic process. In addition, the laser power dependence showed that the thickness of W films linearly increases with power; however, the thickness decreased significantly at a sufficiently high power to allow the evaporation of tungsten oxide.Various analyses (X-ray diffraction (XRD), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS)) identified α-W, WO2, and WO3 in the deposited W films at 1.78–6.67W and at a scan rate of 4μm/s, and their compositional and microstructural changes according to laser power. The loss of carbon (C) is attributable to the background oxygen. An increase in laser power increased the oxygen content, the WO3 to WO2 ratio, and the size of W grains. The resistivity of W films was closely related to the oxygen concentration and microstructure of W. The minimum resistivity of ~80μΩ-cm was obtained at a power of from 3.56 to 4.0W, at which the effect of the laser-induced grain growth on resistivity is maximized, accompanied by the laser-enhanced oxidation of W.

Temperature-dependent photoconductance of heavily doped ZnO nanowires

Ga-doped ZnO nanowires have been synthesized by a pulsed laser chemical vapor deposition method. The crystal structure and photoluminescence spectra indicate that the dopant atoms are well integrated into the ZnO wurtzite lattice. The photocurrent properties at different temperatures have been systematically investigated for nanowires configured as a three-terminal device. Among the experimental highlights, a pronounced semiconductor-to-metal transition occurs upon UV band-to-band excitation. This is a consequence of the reduction in electron mobility arising from the drastically enhanced Coulomb interactions and surface scattering. Another feature is the reproducible presence of two resistance valleys at 220 and 320 K upon light irradiation. This phenomenon originates from the trapping and detrapping processes in the impurity band arising from the native defects as well as the extrinsic Ga dopants. This work demonstrates that due to the dimensional confinement in quasi-one-dimensional structures, enhanced Coulomb interaction, surface scattering, and impurity states can significantly influence charge transport. Open image in new window

Field effect transistor based on single crystalline InSb nanowire

InSb nanowires with zinc-blende crystal structure and precise stoichiometry are synthesized via pulsed-laser chemical vapor deposition. Raman spectroscopy shows Stokes and anti-Stokes peaks of transverse-optical mode with asymmetric broadening. The nanowire demonstrates n-type semiconductor behavior. Enhanced surface scattering due to size confinement leads to reduced electron mobility.

Rapid nucleation of diamond films by pulsed laser chemical vapor deposition

The nucleation of diamond films could be greatly enhanced on mirror-polished Si substrate by a pulsed Nd:YAG laser beam without any thermal- and plasma-assisted processes during a very short time. The nucleation density increased with decreasing laser power density from 1.38×10 10 to 1.17×10 9 W/cm 2 and deposition pressure from 1013 to 4 mbar. The pulsed laser beam made no contribution to enhance nucleation at substrate temperature as low as 650°C. X-ray diffraction measurements showed the (1 1 1) diffraction peak of diamond for the samples obtained using only pulsed laser during 40 min. The enhanced nucleation and growth of diamond crystallites were attributed to effective excitation of reactive gases and etching of non-diamond carbon phases by the pulsed laser beam.