Single crystal growth and transport properties of narrow-bandgap semiconductor RhP₂

We report the growth of high-quality single crystals of RhP₂, and systematically study its structure and physical properties by transport, magnetism, and heat capacity measurements. Single-crystal x-ray diffraction reveals that RhP₂ adopts a monoclinic structure with the cell parameters a = 5.7347(10) Å, b = 5.7804(11) Å, and c = 5.8222(11) Å, space group P2₁/c (No. 14). The electrical resistivity ρ(T) measurements indicate that RhP₂ exhibits narrow-bandgap behavior with the activation energies of 223.1 meV and 27.4 meV for two distinct regions, respectively. The temperature-dependent Hall effect measurements show electron domain transport behavior with a low charge carrier concentration. We find that RhP₂ has a high mobility μ_e ∼ 210 cm²⋅V⁻¹⋅s⁻¹ with carrier concentrations n_e ∼ 3.3 × 10¹⁸ cm⁻³ at 300 K with a narrow-bandgap feature. The high mobility μ_e reaches the maximum of approximately 340 cm²⋅V⁻¹⋅s⁻¹ with carrier concentrations n_e ∼ 2 × 10¹⁸ cm⁻³ at 100 K. No magnetic phase transitions are observed from the susceptibility χ(T) and specific heat C_p(T) measurements of RhP₂. Our results not only provide effective potential as a material platform for studying exotic physical properties and electron band structures but also motivate further exploration of their potential photovoltaic and optoelectronic applications.