Electrical transport and optical properties of hydrogen-deficient YH2 films

We have investigated electron transport characteristics of a hydrogen-deficient dihydride of yttrium YH2+delta (-0.3 < delta < 0.05) focusing particularly on the effect of hydrogen deficiency on carrier relaxation time. At room- and low-temperatures, dc-specific resistivities obtained from electrical measurements show minimum values when hydrogen-deficient quantity delta is approximately -0.1. Optical conductivities were obtained from reflectance measurements by the Kramers-Knonig transformation. When delta is changed, the carrier scattering rate determined from the optical conductivity shows a behavior similar to those of dc resistivities. Not only the carrier scattering rate but also a band-gap energy E-0 associated with a Gamma'(2)-Gamma'(25) transition is influenced by the hydrogen deficiency; E-0 shows a maximum value as delta is about -0.1. Hall coefficients are found to be positive but fairly small (similar to10(-11) m(3)/C), indicating that electrons as well as holes presumably contribute to electric conduction in YH2+delta.