Laser conditioning and electronic defect measurements of HfO2 and SiO2 thin films

摘要

Multilayer HfO(sub 2)/SiO(sub 2) high reflectors (HR) and polarizers show a permanent increase in their 1064-nm damage thresholds following laser conditioning at subthreshold fluences. Threshold increases of 2--3x are typical. In an effort to better understand the conditioning effect we have made laser conditioning and electronic property measurements on single layers of these two materials. The laser damage threshold of 1-(mu)m thick e-beam deposited SiO(sub 2) was increased by laser conditioning for wavelengths ranging from 355 to 1046 nm. The damage threshold of HfO(sub 2) single layers was not influenced by sub-threshold illumination. As-deposited thin films of a-SiO(sub 2) are known to contain paramagnetic electronic defects. We have used electron paramagnetic resonance (EPR) to study the concentrations and types of defects present in single layer and multilayer films of HfO(sub 2) and SiO(sub 2). E(prime) and oxygen hole centers with concentrations on the order of 10(sup 17)/cm(sup 3) have been measured in the SiO(sub 2) layers. A previously unreported defect has been observed for HfO(sub 2). The concentration of defects was studied both before and after laser conditioning and damage with 1064-nm photons. These electronic structure measurements are discussed in relation to an electronic defect model for laser conditioning of dielectric multilayers. 27 refs., 11 figs., 1 tab.