Reactive plasma sputtering deposition of polycrystalline GaN thin films on silicon substrates at room temperature

We report on the successful growth of polycrystalline GaN thin films on Si (100) substrates at room temperature (without intentional heating) using radiofrequency reactive magnetron sputtering. We use Ar and N-2 as the main sputtering and N-atom precursor gas sources, respectively, and a gallium cathode as the Ga-atom source. We focus here on studying the effect of working pressure, as it is found to be the parameter that plays the most influential role on the crystalline quality of the thin films in the investigated range (20-95 mTorr). The morphology, microstructure, and composition profile of the GaN thin films are analyzed using a set of ex situ solid-state characterization techniques. This study reveals that for process pressures below 50 mTorr, the resulting films possess an amorphous nature, while for process pressures above that they become polycrystalline. Most of the crystalline films are found to be nanostructured with grain sizes typically ranging from 10 to 30 nm in size. The highest growth rate of similar to 2.9 angstrom/s is obtained for the deposition carried out at 50 mTorr. At this pressure, the films exhibit the best crystallinity with a dominant wurtzite hexagonal structure. The elemental distribution of Ga and N throughout the growth profile is uniform with a sharp interface at the substrate, demonstrating one of the interests in working at low temperatures to avoid melt-back etching, a destructive reaction between gallium and silicon, that usually takes place at high temperatures.

Automated summary

We successfully grew polycrystalline GaN thin films on Si (100) substrates at room temperature using radiofrequency reactive magnetron sputtering, with Ar and N-2 as the main sputtering and N-atom precursor gas sources, respectively. The effect of working pressure on the thin film's crystalline quality was studied, and it was found that pressures below 50 mTorr result in amorphous films, while pressures above 50 mTorr result in polycrystalline films. The films grown at 50 mTorr exhibited the best crystallinity with a dominant wurtzite hexagonal structure, and a uniform elemental distribution of Ga and N throughout the growth profile.