INFLUENCE OF PREPARATION CONDITIONS ON THE ELECTRICAL CONDUCTIVITY OF GaN THIN FILMS

Background. Gallium nitride (GaN) is a promising material for the developing of LEDs, lasers, ultraviolet detectors, and high-frequency transistors. The properties of GaN significantly depend on the type of defects and the parameters of thin film production. In particular, substrates, buffer layers, sputtering temperature, and partial pressure of the working gas have an impact. This led to studying the electrical conductivity of GaN thin films obtained by radio-frequency (RF) ion-plasma sputtering under different technological conditions. Materials and Methods. GaN films with a thickness of 0.3..1.0 μm were deposited on sapphire and quartz substrates, with/without buffer layers of MgAl₂O₄ or ZnO. RF sputtering was carried out in a N₂ atmosphere at a pressure of 5×10 –3 .. 5×10 –2 Torr and temperatures of 400-650 °C. The structure was analyzed by X-ray diffraction, and the electrical conductivity was determined in the temperature range of 100..450 K by the method of two-point contacts using ohmic carbon contacts. Results and Discussion. It was found that GaN films have a polycrystalline structure with different orientations, depending on the type of substrate and the presence of a buffer layer. The resistivity varies from 10⁵ to 10¹⁰ ohm-cm. High-impedance samples are characterized by a thermal activation energy of 0.34 eV, and the donor type of conductivity in the films has been established. In the films on quartz substrates with a ZnO sublayer, lower activation energy values (0.004..0.05 eV) were recorded, indicating a different conduction mechanism. The conductivity of GaN increases with increasing substrate temperature and decreasing partial pressure of N₂ in the sputtering atmosphere, which leads to the formation of nitrogen vacancies – the main donor defects. Conclusion. The conditions of their preparation largely determine the electrical conductivity of GaN thin films. The most important factors are the type of substrate, buffer layers, sputtering temperature, and gas pressure in the sputtering atmosphere. The obtained dependences of the change in the electrical conductivity of GaN thin films on the partial pres­sure of the working nitrogen gas and the temperature of the substrate during sputtering show that the most likely defects of the donor type in gallium nitride are nitrogen vacancies V N . Keywords : thin films, gallium nitride, electrical conductivity, donor defects.