Piezoelectric and non-linear optical properties of α-quartz type Si1−xGexO2 single crystals

Abstract

Single crystals of α-quartz type Si_1−xGe_xO₂ with x < 0.2 were grown in 0.05 M NaOH solution. Infrared measurements confirmed that crystals grown at high pressure and high temperature have a low –OH group defect content. After a few millimeters of crystal growth under these conditions, α₃₅₀₀ reaches 0.1 cm⁻¹ and no free –OH are present. The d₁₁ value measured on an X-cut from the crystal with x = 0.0375 is 3.08 pC N⁻¹ (±0.15), in good agreement with the value of 2.97 pC N⁻¹ obtained using density functional theory based calculations. Piezoelectric measurements were performed on the Si_1−xGe_xO₂ crystal with x = 0.0375, both at room temperature and after annealing at various temperatures. The piezoelectric signal of the crystal with x = 0.0375 and pure SiO₂ disappears after annealing at 635 °C and 545 °C, respectively. Nonlinear optical (NLO) properties of Si_1−xGe_xO₂ crystals were measured by Maker's fringe technique on Z-cut χ₁₁⁽²⁾ and their corresponding values for x = 0.023 and 0.028 are 1.3(2) pm V⁻¹ and 1.6(2) pm V⁻¹, respectively. These values are in good agreement with density functional theory based calculations. The light induced damage threshold values measured on Si_1−xGe_xO₂ crystals with x = 0.023 and 0.028 are very similar to that of α-quartz.