Transparent yttrium hydride thin films prepared by reactive sputtering

Abstract

Metal hydrides have earlier been suggested for utilization in solar cells. With this as a motivation we have prepared thin films of yttrium hydride by reactive magnetron sputter deposition. The resulting films are metallic for low partial pressure of hydrogen during the deposition, and black or yellow-transparent for higher partial pressure of hydrogen. Both metallic and semiconducting transparent YH x films have been prepared directly in-situ without the need of capping layers and post-deposition hydrogenation. Optically the films are similar to what is found for YH x films prepared by other techniques, but the crystal structure of the transparent films differ from the well-known YH 3−η phase, as they have an fcc lattice instead of hcp.

Photochromism of rare-earth metal-oxy-hydrides

“…In contrast to what was previously reported by Mongstad et al, 6,7 we do not always obtain transparent and photochromic films after reactive sputtering of Y in Ar/H 2 mixtures followed by exposure to air. Uncapped films prepared below a certain critical deposition pressure remain dark metallic upon exposure to air.…”

“…To investigate the effect of different cations and postdeposition oxidation on the thin film crystal structure, the lattice constants are summarized in 7 In comparison, we observe significantly smaller lattice constants in Pd capped YH 2 , DyH 2 , and ErH 2 thin films prepared by sputtering of metal layers in pure Ar followed by a separate hydrogenation step at p H2 ¼ 1 bar at RT (full red diamonds). These results are closer to the reference values which represent highly ordered structures obtained by hydrogenation of (bulk) metals at elevated temperatures.…”

“…6 This polycrystalline semiconductor has an optical bandgap of about 2.6 eV and an fcc crystal structure with a lattice constant of 5.35-5.40 Å . 7,8 The initially transparent material photodarkens in a wide spectral range covering the visible (VIS) and near infrared (NIR) with a time constant in the order of minutes. 6 Hence, YO x H y is a promising material for application in energy saving smart windows and other chromogenic devices.…”

Engineering of the band gap and optical properties of thin films of yttrium hydride

“…The main recorded reflection peaks (111), (200), (220), (311), and (331) were indexed with the space group Fm 3m similar to that known for YH 2 . 12 The intensity of the (200) and the (311) peaks was seen to decrease when increasing the deposition pressure from 1 to 3 Pa. This result might be related to a difference in film texture (orientation) or to a change in the oxygen lattice.…”

“…Table I displays the direct band gaps, E dir g , estimated from the transmittance and reflectance spectra according to the procedure described in Ref. 12. Analysis shows that E dir g increases with increasing deposition pressure.…”