Correlating Photoconductivity and Optical Properties in Oxygen‐Containing Yttrium Hydride Thin Films

Abstract

Oxygen‐containing yttrium hydride (YHO), primarily known for its photochromic properties, simultaneously shows a photoconductive response. Polycrystalline YHO thin films are deposited by reactive magnetron sputtering onto glass substrates and their optical and electrical properties are correlated under illumination with light. While photoconductivity is found in a broader range of compositions than photochromism, maximum photoconductive response is found for samples exhibiting photochromism. This photoconductive effect can be observed above a certain cutoff energy of light and a stronger response is triggered by shorter wavelengths. After the illumination is stopped, the slow recovery (few minutes) of the optical transmission and electrical transport suggests that the underlying process is not purely electronic. A memory effect is found depending on the previous exposure of samples to light which supports the hypothesis of local hydrogen diffusion during the photochromic reaction. An unprecedentedly fast bleaching speed is reported for samples stored in vacuum immediately after film deposition.

Modification of the Photochromic Properties of Oxygen-Containing Yttrium Hydride by Irradiation with keV and MeV Ions

“…Thin films of YHO are typically produced by either reactive magnetron sputtering or e – beam evaporation of yttrium dihydride followed by oxidation and they show photochromic properties in a range of chemical compositions with the oxygen to yttrium ratio δ of 0.5 < δ < 1.5 . Moreover, photochromism is commonly coupled to photoconductivity, , even though the latter one is also found in YHO films with δ < 0.5 …”

“…9 Moreover, photochromism is commonly coupled to photoconductivity, 3,10 even though the latter one is also found in YHO films with δ < 0.5. 11 While the dependency of the photochromic behavior of YHO on chemical composition, thickness, and environment have been studied extensively, 9,12 the fundamental mechanism underlying the photochromic effect remains debated. For GdHO thin films, Hans et al showed a dual-phase nature of the material and proposed a photoinduced transfer of hydrogen between the two phases linked to the residual stress of several GPa as a mechanism of the photochromic behavior.…”