Lattice disorder in implanted insulators: Pb implantation in α-Al2O3

Abstract

The effects of 20, 50 and 100 keV Pb ion implantation on α-A1₂O₃ single crystals have been investigated using the Rutherford backscattering channeling technique. Lattice disorder is observed to reach saturation at Pb doses greater than 10¹⁵ ions/cm². Analysis of the implantation and damage profiles reveals that migration of defects occurs during implantation. It is found that the average threshold displacement energy, obtained from the measured number of displaced lattice atoms using the Kinchin-Pease equation, is dependent on implantation energy. This is discussed in terms of lattice reordering during ion bombardment which depends on the substrate temperature. The lowest value of the average displacement energy, obtained from the 20 keV samples, is 14 ± 2 eV, in reasonable agreement with the calculated Frenkel pair formation energy in α-A1₂O₃. Lattice locations for {0110} and {1212} configurations show that the implanted Pb atoms are almost substitutional along the A1 rows. The substitutional fraction reaches a value of about 80% at an implantation dose of 10¹⁴ ions/cm². Post-implantation annealing experiments indicated a degree of correlation between Pb migration and lattice damage recovery.