Epitaxial growth of garnets for thin film lasers

Abstract

Liquid phase epitaxial techniques have been developed for the preparation of thin films of optical materials. Heteroepitaxy of magnetic garnets on nonmagnetic garnet substrates by the dipping technique employs the phenomenon of stable supersaturation in the iron garnet-PbO:B₂O₃ system. Rare earth aluminum garnets in the same flux supersaturate to a lesser extent and precipitate readily upon substrate insertion. High quality films of YAG:Nd and YAG:Yb,Er,Tm,Ho on pure YAG as well as pure YAG on YAG:Nd have been prepared from a saturated PbO:B₂O₃₊ flux using a transfer technique. Laser oscillation of Ho³⁺ at 2.1μm and Nd³⁺ at 1.06μm in single crystal epitaxial films prepared by the transfer technique have been reported by van der Ziel et al. Solute transfer has the advantage in optic garnet systems of uniform film growth at constant temperature without spontaneous nucleation. In addition, continuous solution of uniform composition nutrient maintains the rare earth dopant concentration in the melt. Pb incorporation results in a brown discoloration but can be eliminated by the proper choice of growth temperature. Deposition rates between 2 μm and 6 μm/hr. at ∼1O00°C have been found satisfactory. In this paper melt preparation, furnace design, the effect of impurities on threshold, and the effects of lattice mismatch and substrate orientation will be discussed.