INVESTIGATION OF GALLIUM NITRIDE ISLAND FILMS ON SAPPHIRE SUBSTRATES VIA SCANNING ELECTRON MICROSCOPY AND SPECTRAL ELLIPSOMETRY

Resumo

Gallium nitride (GaN) seed sub 100 nm layers deposited from triethyl gallium and ammonia on sapphire substrates in different modes during atomic-layer epitaxy (ALE) have been studied via scanning electron microscopy (SEM) and spectral ellipsometry. The seed layers are island films with different degrees of substrate surface coating, which consist of GaN crystallites having different sizes and average thicknesses from 10 to 40 nm. A program for processing SEM images has been developed, which allows us to quantitatively estimate areas of particles, inclusions, and phases present in films and on the substrate surface. The technique of processing the results of spectral ellipsometric measurements of island films composed of GaN crystallites on sapphire substrates using the Maxwell–Garnett model reveals the same tendency in the area of substrates coated with the films as the processing of SEM images. The developed program and technique made it possible to determine the optimal mode (among six implemented) of ALE of GaN seed layers on sapphire substrates for preparation of high-quality HEMT structures. They can also be efficiently used for studying any island films, layers with inclusions of physical and chemical phases, and systems of colloidal particles used for formation of microelectronic structures.