Growth and Characterization of ScGaN Thin Films Using DC Magnetron Sputtering

Sammanfattning

This diploma work explores the growth, characterization, and optimization of ScxGa1-xN thin films on sapphire and silicon substrates using direct current magnetron co-sputtering. The objective is to improve the crystalline quality of ScxGa1-xN to investigate its ferroelectric properties, driven by the growing demand for advanced information storage technologies. The research methodology involves refining the deposition system, calibration of substrate surface temperature, determination of growth rate, and conducting depositions with varying growth conditions. The investigation includes several series with varying Sc concentrations and interlayer configurations to assess their effect on crystalline quality. The first series examines the effect of varying Sc concentration (0% to 100%) relative to Ga concentration on sapphire substrates. The second series focuses on the growth of ScxGa1-xN films, with Sc concentrations from 10% to 50%, with inserting a TiN seed layer on sapphire. The TiN is acted as a bottom electrode and can reduce lattice mismatch between the film and substrate. To facilitate ferroelectric measurements, films of Sc0.05Ga0.95N, Sc0.25Ga0.75N and Sc0.37Ga0.63N, with a thickness of approximately 250 nm, were deposited with a pure Ti top electrode. Additional samples with a thinner 30 nm film and Ti top electrode were also produced for ferroelectric measurements. The third series includes a sapphire substrate with an AlN nucleation layer and a GaN buffer layer beneath the ScxGa1-xN film. The fourth series mirrors the third, substituting sapphire with HF-treated silicon (111). To determine the structural properties, these ScxGa1-xN films were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD) for investigating morphology, composition, and crystallinity, respectively. Results from the first series demonstrated that increasing Sc concentration up to 24% doesn’t affect the crystal quality much, evidenced by a small peak angle shifts in XRD measurement. However, beyond 24% Sc, the films exhibited a structure where the long-range order is lost due to lattice disorder. Electrical measurements revealed a sharp increase in sheet resistance with low Sc concentrations, making it unmeasurable between 14% and 54% Sc levels. Yet, at high Sc concentrations, sheet resistance decreases. Results from the second series revealed similar trends for the crystal quality measurements as the first series. For the electrical measurement, excessive resistive leakage between the top and bottom electrodes unfortunately made it impossible to obtain any meaningful ferroelectric data. In the third and fourth series, incorporating different interlayers and substrates allowed for higher Sc concentration without degrading film quality. However, due to the overlapping XRD peaks of GaN buffer layer and ScxGa1-xN, it was difficult to provide conclusive evidence of this improvement.