High-quality epitaxial growth of ferroelectric Al0.9Sc0.1N on GaN by pulsed laser deposition

Abstract

In this study, high-quality wurtzite Al0.9Sc0.1N thin films were grown on GaN templates via pulsed laser deposition (PLD). The influence of in situ thermal pretreatment of the substrate, growth temperature, and laser repetition rate on the microstructural evolution and electrical properties of the films was investigated. As revealed by in situ x-ray photoelectron spectroscopy, surface oxides are effectively removed through in situ thermal cleaning at 850 °C, and this step facilitates the nucleation of the (0002) orientation. Regarding growth kinetics, optimization results show that an ideal kinetic window for adatom migration is provided by a substrate temperature of 550 °C combined with a low laser repetition rate of 2 Hz. Under these optimized conditions, exceptional crystalline quality was achieved. A record-low full width at half maximum (FWHM) of approximately 180 arc sec was recorded for the (0002) plane in the x-ray rocking curve, while an FWHM as low as 175 arc sec was observed for the (101¯2) plane. This performance is comparable to state-of-the-art thin films fabricated via molecular beam epitaxy and sputtering. As revealed by temperature-dependent electrical characterization, the leakage current mechanism is dominated by Schottky emission at low electric fields, transitioning to Poole–Frenkel emission at high electric fields. Dielectric performance was significantly enhanced by the superior crystalline quality of the sample grown at 2 Hz, yielding a breakdown field of approximately 12.7 MV/cm (breakdown voltage approximately 57 V). Furthermore, distinct ferroelectric switching characteristics were exhibited by the optimized films. Collectively, these results demonstrate PLD as a competitive, cost-effective technique.