Structural and Thermoelectric Properties of Black Arsenic–Phosphorus

Here, we report the structural and temperature-dependent transport properties of AsxP1–x (x = 0, 0.2, 0.5, 0.83, and 1) alloys. It is observed that black phosphorous-related phonon modes in the alloy samples are redshifted with increasing arsenic concentration, while black arsenic-related modes in these samples are blueshifted with increasing phosphorus concentration. As the arsenic concentration x increases from 0 to 1, the 4-probe resistance of the AsxP1–x alloys is found to decrease by more than 3 orders of magnitude. The transport studies reveal that samples with the highest arsenic concentration (x = 1 and 0.83) show metallic behavior in the temperature dependence of resistance with small thermopower at room temperature with an anomalous temperature dependence. In contrast, the samples with high phosphorus concentration (x = 0, 0.2, and 0.5) show very large thermopower values at room temperature, reaching a value as high as 803 μV/K for x = 0.2. The temperature dependence of the thermopower of these samples can be well described by the two-dimensional (2D) variable range hopping (VRH) mechanism, S ∼ T1/3. Similarly, their 4-probe resistance (R) values can be fitted with the 2D VRH mechanism, R ∼ exp(T–1/3).