Fabrication and characterization of Mg-Ni hydride thin films for photovoltaic applications

We prepared and characterized three different compositions of the novel semiconductor material Mg2.0NiH4, Mg2.2NiH4 and Mg2.4NiH4 as thin films for photovoltaic applications. The thin films were deposited using reactive sputtering at room temperature, to achieve crystallization the samples were annealed at 220C and 290C. The composition of the samples were determined with EDS and the structural properties of the samples were then investigated using XRD and Raman spectroscopy. The band gap for the different compositions and annealing processes were calculated using a Tauc-plot. We did Hall-measurements to investigate the electronic properties such as mobility, density and charge-carrier in the samples while the resisitivity were measured using a four point probe. Also during the annealing process an unexpected color change appeared in the crystalline Mg2.4NiH4 samples. This thermochromic effect were investigated with transmission and reflection spectroscopy, which indicates a band gap narrowing. XRD measurements with variable temperature were also performed to investigate if any structural change occurs during heating