Optical absorption in ion-bombarded magnetic garnet films

Abstract

Optical absorption measurements are reported for the damaged surface layers produced by proton and neon bombardment of iron‐garnet liquid‐phase‐epitaxialfilms. The excess optical absorption is shown to be an absorption tail on O(2p)→Fe(3d) charge‐transfer bands centered near 4 eV with about 10% contributed by higher‐energy optical transitions. The distribution of states for Ne bombardment is different from that for H bombardment, and in the case of Ne the state distribution depends on the dose. Saturation at a photon energy of 2.2 eV occurs at an absorption coefficient of ∼2×104 cm−1. The average damage density over the damaged layer thickness is observed to increase with decreasing H energy, in agreement with hard‐bubble‐suppression data and nuclear stopping power considerations. Based on optical absorption and hard‐bubble‐suppression results it is estimated that the dose window for hard bubble suppression corresponds roughly to an average disorder range from ∼3–30% amorphous (amorphous defined optically). Annealing studies show that no simple activation energy description applies to the damaged material. Deep states anneal out more rapidly than shallow states for both H and Ne bombardment.