Large-Area MoS₂ Films Grown on Sapphire and GaN Substrates by Pulsed Laser Deposition

In this paper, we present the preparation of few-layer MoS₂ films on single-crystal sapphire, as well as on heteroepitaxial GaN templates on sapphire substrates, using the pulsed laser deposition (PLD) technique. Detailed structural and chemical characterization of the films were performed using Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction measurements, and high-resolution transmission electron microscopy. According to X-ray diffraction studies, the films exhibit epitaxial growth, indicating a good in-plane alignment. Furthermore, the films demonstrate uniform thickness on large areas, as confirmed by Raman spectroscopy. The lateral electrical current transport of the MoS₂ grown on sapphire was investigated by temperature (T)-dependent sheet resistance and Hall effect measurements, showing a high n-type doping of the semiconducting films (n_s from ~1 × 10¹³ to ~3.4 × 10¹³ cm^-2 from T = 300 K to 500 K), with a donor ionization energy of E_i = 93 ± 8 meV and a mobility decreasing with T. Finally, the vertical current injection across the MoS₂/GaN heterojunction was investigated by means of conductive atomic force microscopy, showing the rectifying behavior of the I-V characteristics with a Schottky barrier height of ϕ_B ≈ 0.36 eV. The obtained results pave the way for the scalable application of PLD-grown MoS₂ on GaN in electronics/optoelectronics.