Investigation of optical loss mechanisms in oxide thin films Page: 4 of 13
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phase-matching, high damage threshold, and transparency in the appropriate
wavelengths. Moreover, higher power densities can be achieved in a thin film
waveguide configuration due to beam confinement, and direct integration with present
semiconductor materials is possible.2
Although SHG has been demonstrated recently in KNbO3 thin films,3 the high
losses present in most film-waveguides are problematic and must be overcome for
practical device applications. The research focused on the breakdown of loss
mechanisms is at a nascent stage; several groups have generated valuable models.4 We
approach the problem of the high KNbO3 losses by studying oxide systems with simpler
structures where specific loss mechanisms are eliminated and isolated in order to
understand their contribution to losses.
The microstructural and optical properties of the KNbO3 films are summarized
as reported by previous work.5 Basic loss theory is addressed where the relevant
mechanisms are noted. Tetragonal potassium tantalum niobate (K(Ta,Nb)03), cubic
potassium tantalate (KTaO3), and amorphous tantalum oxide (Ta205) films were
deposited by ion-beam sputtering and their properties and pertinence to the loss study
are discussed. The characterization techniques used include prism-coupling to measure
the refractive index, an optical fiber loss method to quantify the optical scattering losses,
atomic force microscopy (AFM) to probe surface roughness, and elastic resonant
scattering to analyze oxygen composition.
KNbO FILMS
Ion-beam sputter deposition was used to deposit all the oxide films. For KNbO3 film
deposition, two potassium superoxide (K02) targets and one niobium target were
sequentially sputtered. The details of the deposition process can be found in another
paper.5 The films were grown on MgO, MgA12O4, and KTaO3 substrates. X-ray
diffraction (XRD) revealed the films to be orthorhombic (110) single orientation. XRD
rocking curves, Rutherford backscattering spectrometry (RBS) channeling, and
transmission electron microscopy diffraction analyses showed the films to possess a high
degree of epitaxy. Small grain sizes (1000 to 5000 A) were detected and the film
surface roughnesses were low with root mean square (rms) values between 9 and 37 A
by AFM. The refractive indices approach bulk values indicating dense films. These
results are summarized in Table I.
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Chow, A. F.; Kingon, A. I.; Auciello, O. & Poker, D. B. Investigation of optical loss mechanisms in oxide thin films, report, May 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc793455/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.