We conducted DC and double AC Hall effect measurements, as well as temperature-dependent thermoelectric characterization of three films. They have the following compositions: Cu 2.50 P (labeled "Cu 3-z P"), Cu 1.61 P, and CuP 1.35 (labeled "CuP 2-y "). We use these labels to emphasize similarity to Cu 3 P and CuP 2 as discussed in the previous section. This set of films was deposited on Si 3 N 4 membranes as part of a microchip-based thinfilm transport characterization platform. Differences between this set of films and the films deposited on glass characterized in the rest of the article are listed in the Supporting Information. Since these films have intermediate compositions between CuP 2 and Cu 3 P, their prop- Electrical conductivity (S/cm) erties may be influenced by inhomogeneity, as exemplified by the dual-phase morphology shown in Fig. . Nevertheless, important qualitative trends in the transport properties of these films as a function of composition can still be discerned. The temperature dependence of the electrical conductivity (Fig. ) suggests that CuP 2-y is a nondegenerately doped semiconductor and that the two other films are either metallic or degenerately doped semiconductors. Hall effect measurements at room temperature confirm this interpretation (Fig. ), with high carrier concentrations measured in Cu 3-z P and Cu 1.61 P (above 10 20 cm -3 ) and a moderate carrier concentration measured in CuP 2-y (10 15 cm -3 -10 17 cm -3 ). All films have a positive Hall voltage confirming their p-type conductivity. Note that the conductivity of Cu 1.61 P and CuP 2-y after one month of storage is appreciably lower (Fig. (a)), highlighting possible stability issues as discussed in the previous sections.