R.R. Parsons

Optical properties and microstructure of reactively sputtered indium nitride thin films

The optical properties of reactively sputtered InN thin films were measured in the spectral region 2.5–5.5 eV using spectroscopic ellipsometry. The measured pseudodielectric function data of the InN films were found to vary with deposition power. The effective medium approximation theory, which describes a random aggregate microstructure, was able to relate the differences in the measured optical properties to the surface microroughness and porosity of the InN films. The relationship between microstructure and deposition power was subsequently verified by scanning electron microscopy. The analysis and electron microscopy indicate that the film deposited at 90 W was most representative of InN.

Bi-Sr-Ca-Cu-oxide superconducting thin films deposited by dc magnetron sputtering

Thin films of the high‐temperature superconductor Bi‐Sr‐Ca‐Cu‐oxide were deposited by dc magnetron sputtering onto various substrates. Films deposited on (100) MgO substrates achieved zero resistance between 78 and 82.5 K depending upon the annealing conditions. The best films were produced with a quick post‐anneal in oxygen at 870 °C followed by a slower anneal in air at the same temperature. The composition of the sputtered films was uniform within ±3% over an area 40 mm in radius, and films deposited at 15 and 40 mm from the center of deposition both exhibited high Tc transitions.

Properties of transparent, conducting ZnO films deposited by reactive bias sputtering

Transparent ZnO thin films of resistivity 2×10−3 Ωcm have been prepared by a reactive bias sputtering technique. Carrier concentration and mobility were determined by Hall probe measurements. Microstructure and grain size were studied using a scanning electron microscope and an X-ray diffractometer. Optical constants were measured for the wavelength range 0.35 to 2.50 μm and infrared reflectivity for the range 2.5 to 20 μm. These optical properties were modelled by the Drude theory of free electrons utilizing measured electrical transport parameters.

Effects and loss of lead in doped Bi-Sr-Ca-Cu-O films

Films of Bi‐Sr‐Ca‐Cu‐O, with and without lead doping, were prepared by rf magnetron sputtering of oxide targets. The films were annealed in oxygen for varying durations and characterized by electron microprobe and x‐ray diffraction. The results show a drastic loss of lead during annealing. Films with the lead‐enhanced Bi2Sr2Ca2Cu3Oy (2223) phase had no detectable lead after annealing. The films were seen to grow in stages of 2201, 2212, and finally 2223 phases. The lead affected film development through these stages.

The infrared properties of magnetron-sputtered diamond-like thin films

Abstract We have measured the infrared reflectance, R , and the transmittance, T , of several amorphous and diamond-like carbon films deposited on GaAs substrates by d.c. magnetron sputtering in an Argon atmosphere. The thickness, d , and the refractive index, n , were found from the fringes in the near-infrared reflectance, which were due to the interference in the film, using an appropriate model for the absorption. The mid-infrared absorption coefficient α, obtained from 1- R - T , was then fitted to a model of the absorption involving both vibrations and electronic transitions, using d and n . The electronic absorption was found to decrease with increasing pressure, along with an increase in the intensity of the hydrogen vibrational features. We associate the transparency with the presence of hydrogen and present support for this view by measuring a film in which hydrogen was deliberately introduced.

Long lifetime photoluminescence from a deep centre in copper-doped silicon

Abstract Intense, long lived photoluminescence lines with a complex local mode phonon structure are reported in copper-doped silicon. The spectra and luminescence decay times are both studied as a function of sample temperature. We interpret all of these lines as arising from the recombination of excitons bound to a single type of copper-related isoelectronic defect.

Inconel/carbon multilayers for X-ray mirrors

Abstract The objective is to find new materials for the fabrication of X-ray mirrors with high reflectance at 45 A wavelength, at normal incidence. We have examined multilayers of inconel and carbon, which have high theoretical reflectivities. Planar magnetron sputtering was used to fabricate mirror samples (period = 22.5 A) on silicon substrates. Our best 30-period inconel/carbon multilayers had a reflectivity of 0.3%, which was about a factor of 20 below the theoretical maximum (5.5%). Experimental details presented here include our use of an in situ ellipsometer to monitor the thickness of the layers and to provide information on the early stages of film growth and interdiffusion at the interfaces. Interdiffusion was found to occur at the carbon-on-inconel interface because of the rough underlying inconel layer, but not at the inconel-on-carbon interface because of the smooth underlying carbon layer. Interdiffusion at the carbon-on-inconel layer was also found to increase with the number of layers. The accuracy of ellipsometry for monitoring film thickness during deposition was limited by the theoretical model used for the optical constants of the film. As a result, we were not able to improve on the standard technique of ‘timing’ for control of layer thicknesses.

Optimization of Pb-Bi-Sr-Ca-Cu-O thin films for zero resistance above 100K

Abstract Thin films of lead doped Bi-Sr-Ca-Cu-O have been prepared with zero resistance transition temperatures as high as 106K. These were prepared by RF magnetron sputtering of complex oxide targets followed by air or oxygen annealing. The optimum initial lead concentration for maximizing the amount of the 2223 phase was found to be approximately Pb1.1Bi2Sr2Ca2Cu3Oy. The highest Tc was obtained when the films were processed in an oxygen atmosphere at a temperature of 865°C for a minimum of 16h.

Characterization of magnetron-sputtered diamond-like thin films for optical coatings in IR

Abstract The microstructural, optical, mechanical and electrical properties of diamond-like carbon films prepared by d.c. magnetron sputtering have been investigated as a function of argon pressure and substrate bias. The films were characterized by spectroscopic ellipsometry, scanning and transmission electron microscopy, electron diffraction, resistivity and hardness measurements. The pseudoband gap was found to rise and the hardness decrease with increasing pressure. Ellipsometric modelling indicated a change in the bonding configuration under the above conditions. This effect does not appear to be the result of a change in the energetics of the bombarding ions. Increasing substrate bias resulted in a densification of the films.

Improving the radiative yield of GaAs by laser annealing

We have measured the photoluminescence properties of laser‐annealed single‐crystal GaAs. The quantum efficiency of the band‐edge emission at liquid helium temperatures was increased by 3 orders of magnitude after a single 10−3‐s pulse of ruby laser light. This increase in radiative efficiency is thought to be due to dissociation of Si‐donor‐Ga‐vacancy complexes, which is expected to decrease nonradiative processes and possibly increase radiative centers. A theoretical prediction of the temperature distribution at the end of the laser pulse was performed.