Cathodoluminescence Microanalysis of the Defect Microstructures of Bulk and Nanoscale Ultrapure Silicon Dioxide Polymorphs for Device Applications

Abstract

Cathodoluminescence (CL) techniques have been used to investigate the defect structures of a variety of bulk and nanoscale ultrapure synthetic silicon dioxide (SiO2) polymorphs. CL microanalysis in an electron microscope enables the detection of defect centers with high sensitivity and high spatial resolution. The defect microstructures of a variety of pure silicon dioxide polymorphs have been systematically analyzed using CL microanalysis techniques: The CL microanalysis of SiO2 polymorphs can be challenging as their defect structure may be modified by electron irradiation. Bulk synthetic crystal and amorphous SiO2, SiO2 surface layers (ranging between 50–900 nm thick) on silicon and in situ buried SiO2 in silicon (synthesized using oxygen ion implantation and high temperature annealing processes) have been investigated and their characteristic defects have been determined and compared. The CL emission from pure SiO2 polymorphs is generally related to local point defects in the tetrahedrally coordinated SiO2 host lattice. CL emissions associated with non bridging oxygen defects, oxygen deficient defects and the radiative recombination of the self trapped exciton are observed from bulk and thermal thin films of SiO2 polymorphs. CL emission associated with very low concentrations of substitutional Aluminium impurities is also observed from bulk specimens of Type I and II a-SiO2. In contrast, the CL emission from buried SiO2 in silicon is dominated by emission associated with Si–SiO2 interfaces and Si nanoparticles which form during synthesis.