Growth of sapphire thin films by pulsed laser deposition

Abstract

Formation of sapphire thin films, and most particularly sapphire waveguides, is of great importance in the context of optical and opto-electronic devices. Sapphire is the hardest of all oxide crystals, and has a range of physical properties such as thermal conductivity, electrical conductivity and resistance to chemical attack, that make it a superb choice for environments where extended UV transmission, reliability and strength are required.

In the optics arena, titanium-doped sapphire has had a radical impact on the field of tunable lasers. Ti:Al₂O₃ - is an optically pumpable crystal, producing a laser capable of operating between 650 nm and 1100 nm. Typical dopant levels for Ti³⁺ ions are at the ~0.1% level in commercial samples of Ti:Al₂O₃, which yields an absorption coefficient of lambda = 2.0 cm^-1 at 514.5 nm, a suitable wavelength region for optically pumping into the peak of the absorption band at 490 nm.

To date, the fabrication of sapphire waveguides has had mixed success. Ion-beam implantation studies have been carried out using He ions, but the formation of the index barriers required for guidance has necessitated doses exceeding 10¹⁷ ions/cm², which causes surface damage, fracture, and formation of new compounds within the layer. Chemically active ions such as carbon have also been implanted, but the resultant waveguide losses are still high.

An alternative route involving RF sputtering has produced amorphous films, but these are not of the same refractive index as crystalline sapphire, and were susceptible to chemical attack. Further work is in progress on in-diffusion of titanium into sapphire to make waveguiding layers. In this work, we describe our first attempts to grow crystalline films of a - Al₂O₃, sapphire, via PLD.

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Identifiers

ORCID for R.W. Eason: orcid.org/0000-0001-9704-2204

ORCID for S. Mailis: orcid.org/0000-0001-8100-2670

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