Influence of relative positions between RF coil and crucible on sapphire crystals by edge-defined film-fed growth (EFG) technique

Abstract

To obtain the stable temperature field required for growing sapphire crystals, the influence of relative positions between RF coil and crucible on the performances of sapphires produced by edge-defined film-fed growth (EFG) technique was investigated. For comparison, the crucible was located at the top (case A) and the middle (case B) of the RF coil, respectively. Furthermore, the lattice integrities were studied by the double-crystal X-ray diffraction, and the dislocations were observed under the optical microscope and atomic force microscope after corroding in molten KOH at 390 °C. The crystals in case B exhibit better lattice integrity with smaller full width at half maximum of 29.13 rad·s, while the value in case A is 45.17 rad·s. The morphologies of dislocation etch pits in both cases show typical triangular symmetry with smooth surfaces. However, the dislocation density of 2.8×104 cm-2 in case B is only half of that in case A, and the distribution is more uniform, compared to the U-shaper in case A.