Electrical and optical properties of thin films of Pb2+- and Si4+-doped YIG produced by liquid phase epitaxy

Abstract

Thin films of Si⁴⁺‐doped YIG have been grown on Gd₃Ga₅O₁₂ substrates by liquid phase epitaxy. The electrical resistivity, the sign of the Seebeck coefficient, and the optical transmission have been measured for a number of films prepared from the same melt at different growth temperatures in the range 780–960°C. The measurements show a high optical absorption for films prepared at low growth temperatures, while at intermediate temperatures there is a change from p‐type to n‐type conduction. A resistivity maximum and minimum in the optical absorption are also found. The results are discussed in terms of the charge‐compensation mechanism that occurs as Pb²⁺ ions are incorporated from the flux into the films at the lower growth temperatures. It is found that intrinsic donors, probably oxygen vacancies, are present in concentrations up to 0.03 per formula unit. The increase in the optical absorption coefficient, Δα, relative to pure YIG, is proportional to the concentration of nonionized holes, [p], i.e., Δα=α′[p]. The extinction coefficient α′ increases with decreasing wavelength in the wavelength range 0.55–1.0 μm and has the value (1.2±0.3)×10⁴ cm⁻¹ per formula unit at 0.6 μm. With these results it was possible to propose an ionic model for the doped YIG films as $\{{\mathrm{Pb}}_x^{\text{2+}}{\mathrm{Y}}_{\text{3−x}}^{\text{3+}}\mathrm{\}[}{\mathrm{Fe}}_{\text{2−y}}{\mathrm{Y}}_y^{\text{3+}}\mathrm{](}{\mathrm{Fe}}_{\text{3−z}}{\mathrm{Si}}_z^{\text{4+}}){\mathrm{O}}_{\text{12−w}}^{\text{2−}}{\mathrm{[V}}_{\mathrm{Ow}}]$ , where the ionic valence state of the iron ions depends upon the lead and the silicon content and the concentration and valence state of the oxygen vacancies.