Abstract
Growth and characterization of compositionally tuned, ytterbium-doped mixed lutetium-scandium oxide, and pure lutetia and scandia crystalline films are presented. Pulsed laser deposition was employed to grow these sesquioxide films, of thicknesses up to 20 µm, on (0 0 0 1)-sapphire substrates. By varying the atomic ratio of lutetium to scandium in the target, the lattice parameter of the resulting films could be tuned to match that of the single-crystal c-cut sapphire substrate and thereby achieve a lattice mismatch of <0.1%. Optimization of growth parameters led to a reduction of undesirable particulates and scattering points within the film. X-ray diffraction measurements show (2 2 2)-orientated epitaxial growth with crystallinity comparable to bulk crystals. Through pole figure and electron-backscatter imaging measurements, it was found that two inverted cubic lattice orientations grow with micron-scaled domains. Growth of these lattice-matched mixed sesquioxides paves the way for fabrication of high-quality waveguides suitable for generation of ultrashort laser pulses.
Highlights
Sesquioxides, when doped with trivalent rare-earth ions, are established laser crystals, difficult to source commercially [1], owing to their advantageous thermomechanical and optical properties compared with the exemplar medium yttrium aluminium garnet (YAG) [2, 3]
We show the optimization of growth parameters, x-ray diffraction spectra of the different materials, and demonstrate different orientations of growths in these mixed-sesquioxide films
(222) X-ray diffraction (XRD) peak characteristics for mixed-sesquioxide films grown with different substrate temperatures. a) the intensity of the peaks normalised to the thickness of the films/ FWHM of these XRD peaks and (b) the FWHM of the rocking curve measurements
Summary
Sesquioxides, when doped with trivalent rare-earth ions, are established laser crystals, difficult to source commercially [1], owing to their advantageous thermomechanical and optical properties compared with the exemplar medium yttrium aluminium garnet (YAG) [2, 3]. PLD uses a pulsed laser beam to ablate a target material, creating a plume that travels in a vacuum or partial vacuum toward a heated substrate, and under the correct conditions the deposited material grows into a crystalline film. 3. FLUENCE OPTIMISATION Initially, we studied the effect of ablation fluence on the quality of growth from the pure scandia and lutetia targets, with particular focus on the number of observable scattering points in the films. A range of undoped Sc2O3 and Lu2O3 films were grown with the substrate heated to 1430 oC with a UV laser repetition rate of 20 Hz. The films were grown for 30 minutes (36000 pulses) to thicknesses of 2 μm and 1 μm for the scandia and lutetia respectively. Not very different in value, it means that during mixed-sesquioxide growths, a compromise fluence value was needed
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