Epitaxial Zn₃N₂ thin films by molecular beam epitaxy: Structural, electrical, and optical properties

Single-crystalline Zn₃N₂ thin films have been grown on MgO (100) and YSZ (100) substrates by plasma-assisted molecular beam epitaxy. Depending on growth conditions, the film orientation can be tuned from (100) to (111). For each orientation, x-ray diffraction and reflection high-energy electron diffraction are used to determine the epitaxial relationships and to quantify the structural quality. Using high-temperature x-ray diffraction, the Zn₃N₂ linear thermal expansion coefficient is measured with an average of (1.5 ± 0.1) × 10⁻⁵K⁻¹ in the range of 300–700 K. The Zn₃N₂ films are found to be systematically n-type and degenerate, with carrier concentrations of 10¹⁹–10²¹cm⁻³ and electron mobilities ranging from 4 to 388 cm²V⁻¹s⁻¹. Low-temperature Hall effect measurements show that ionized impurity scattering is the main mechanism limiting the mobility. The large carrier densities lead to measured optical bandgaps in the range of 1.05–1.37 eV due to Moss–Burstein band filling, with an extrapolated value of 0.99 eV for actual bandgap energy.