Low-temperature synthesis of gallium nitride thin films using plasma-enhanced atomic layer deposition for nanoelectronics

In this paper, we report on the low-temperature synthesis of gallium nitride (GaN) thin films using plasma-enhanced atomic layer deposition and fabrication of AlN/GaN field-effect transistors for the application of microelectronics. Trimethylgallium [Ga(CH3)3] precursor and trimethylaluminum [Al2(C2H5)6] precursor were used as the Ga source and Al source, respectively, while ammonia (NH3) gas was used as the N source for the growth of semiconducting GaN and AlN thin films. High-resolution transmission electron microscopy was used to analyze the morphology of the GaN thin films, showing polycrystalline structures, and the x-ray diffraction was used to analyze the crystal structures of the GaN thin films, revealing that the GaN film has a dominant (002) hexagonal wurtzite crystal structure. X-ray photoelectron spectroscopy was used to investigate the atomic concentrations in the GaN film, indicating relative atomic concentrations closely matching the expected stoichiometry of GaN. AlN (4 nm)/GaN (9 nm) field-effect transistors were fabricated with a 9 nm-thick GaN film as the active channel material while ring oscillators were fabricated with the AlN/GaN field-effect transistor. The fabricated AlN/GaN transistor presented the excellent electrical property of a n-channel field-effect transistor, and the fabricated oscillator exhibited an excellent waveform with a propagation delay (tp) of 6.3 ns per stage.