CaCuP films were deposited on Corning Eagle XG borosilicate glass and crystalline silicon substrates placed in symmetryequivalent positions with respect to the deposition sources. The deposition technique was reactive radio-frequency (RF) magnetron co-sputtering of metallic Ca and Cu targets in an Ar/PH 3 atmosphere. The total sputter pressure and substrate platen temperature were fixed at 5 mTorr and 490 °C respectively in all depositions. Unless otherwise stated, the films presented in this article have thickness between 200 nm and 300 nm. Most characterization was conducted with mapping-type measurements and the resulting combinatorial characterisation data was managed with the custom COMBIgor suite. The films on Si were employed for Rutherford backscattering, x-ray fluorescence, and ellipsometry measurements. The films on glass were employed for x-ray diffraction, optical transmission and reflection, and electrical measurements. Consistency between the films grown on the two types of substrates is discussed in the ESI. † X-ray diffraction (XRD) measurements were conducted using Cu K α radiation and a 2D detector. Elemental composition and film thickness were determined by x-ray fluorescence (XRF) calibrated by Rutherford backscattering spectrometry (RBS) and spectroscopic ellipsometry. Sheet resistance was measured in the substrate plane with a collinear four-point probe. Temperaturedependent Hall carrier concentration and mobility were measured in the substrate plane in the van der Pauw configuration. The absorption coefficient of a stoichiometric film was determined by measuring transmission T at normal incidence and reflection R at near-normal incidence using an integrating sphere to include the diffuse component of both transmission and reflection. The absorption coefficient α was extracted by a standard relationship (see ESI †). The absorption coefficients of a larger number of samples were obtained using only direct transmission and specular reflection (both at normal incidence) measured in a custom-built setup with mapping capabilities. The optical functions of CaCuP (refractive index and extinction coefficient) extending into the UV range were measured by spectroscopic ellipsometry on a thinner film to minimise scattering and depolarisation effects Further details on the experimental methods can be found in the ESI. †