Jason C. Jones

Dependence of the critical thickness on Si doping of InGaAs on GaAs

The formation of misfit dislocations during the initial stages of relaxation of In0.04Ga0.96As epitaxial layers on (001) GaAs has been studied by in situ high-resolution double crystal x-ray topography during molecular beam epitaxy growth. Relaxation is initially anisotropic with the fast B(g) dislocations being nucleated before the slow A(g) set. On doping with Si up to a maximum concentration of 4×1018 atoms/cm3, an increase in critical thickness was observed for both dislocation sets. The data can be fitted to an extension of the Matthews–Blakeslee model that includes a lattice friction force varying linearly with the dopant concentration.

Sputtered lead scandium tantalate thin films: crystallization behaviour during post-deposition annealing

Lead scandium titanate (PST) thin films were deposited by RF dual magnetron sputtering and then annealed either by vacuum furnace or combined rapid thermal annealing (RTA) and furnace anneal. The film structure was investigated by x-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy techniques. Lead loss was more severe using furnace annealing than the combined RTA and furnace anneal. The annealed films were characterized by the presence of voids and exhibited relaxor ferroelectric characteristics. PST perovskite crystal grains were found to co-exist with pyrochlore matrix in the furnace-only annealed films, whilst in RTA annealed films no apparent pyrochlore morphology was observed in the TEM image. Lead was found to diffuse through the bottom electrode Pt layer during the annealing. Films treated by combining RTA and furnace annealing have shown pyroelectric coefficients under field of up to 500 µC m-2 K-1, a dielectric loss of below 0.007 and a merit figure for thermal detection of 2.5×10-5 Pa-1/2.

Deposition and annealing of lead scandium tantalate thin films for high performance thermal detector arrays

Abstract This paper describes the deposition of thin film lead scandium tantalate (Pb2ScTaO6) for use in ferroelectric microbridge thermal detectors and reports on the effect of post-deposition annealing. Two methods for the sputter deposition of PST are described - one using a single target, the other a new method using two targets. Annealing of the samples is carried out in oxygen using a commercial rapid thermal processor. Materials are characterised by X-ray diffraction and transmission electron microscopy and show that films deposited as PST pyrochlore can be transformed to perovskite by annealing. Some annealed films have shown B-site ordering. Induced pyroelectric coefficients over 1×10−3Cm−2K−1 have been measured in the annealed films.

Sputtered lead scandium tantalate thin films for dielectric bolometer mode thermal detector arrays

Abstract This paper describes the deposition of thin film lead scandium tantalate (Pb2ScTaO6) using a novel two target sputtering technique and reports on the effect of post-deposition annealing. The films are deposited on platinum-coated silicon wafers at 300°C and are annealed at a range of temperatures up to 800°C. Vacuum furnace and rapid thermal annealing (RTA) methods are compared. Materials are characterised by X-ray diffraction and show that the as-deposited films form a weak pyrochlore phase which is transformed to perovskite PST by annealing. At anneal temperatures of 750°C and above superlattice ordering is observed. Compositional measurements using Energy Dispersive Spectroscopy show that Lead loss is more severe using furnace annealing than RTA, and a combined RTA/furnace anneal method is proposed. The films demonstrate relaxor dielectric characteristics. Induced pyroelectric measurements have been made to assess the potential of this material for ferroelectric micro-bridge thermal detectors.

Statistical method for the identification of peak movement in spectral data: application to x-ray diffraction patterns of manganese oxyhydroxides

A fully automated statistical procedure is described for identifying spectral peaks moving in response to a variable parameter. The method is based upon the measurement of intensity at a given point in the spectrum. The variation of intensity in the spectrum at this given point is considered in relation to the variable parameter via a linear regression analysis. If the peak does not move, then the values of intensity versus the variable parameter should show a linear relationship. On the other hand, if there is a peak shifting through this fixed point with change in the variable parameter then the data should show nonlinearity which can be readily identified statistically. The method was applied to the analysis of x-ray diffraction spectra for manganese oxyhydroxides reduced chemically to produce a range of values of . Samples contained shifting peaks which were identified by the method described.

Precursor design for liquid Injection CVD of lead scandium tantalate thin films

Abstract Liquid Injection Chemical Vapour Deposition is a technique well suited to the deposition of a range of ferroelectric oxides in thin film form. This paper reports on the design and optimisation of the precursors for the deposition of thin films of the promising pyroelectric material, lead scandium tantalate. The design and use of lead, scandium and tantalum precursors with carefully matched chemical and thermal properties allows the growth of thin films with the required perovskite phase above 550°C. These have the desired 111 orientation when grown on to platinum coated silicon substrates at temperatures above 575°C.