Gallium nitride thin films deposited by radio-frequency magnetron sputtering

Effects of self-induced negative bias in radio-frequency (rf) sputtering on the structure of the deposited film are discussed on the basis of the measured characteristics of the gallium nitride (GaN) films. A powdered GaN target was sputtered by either argon (Ar) or nitrogen (N2) gas to investigate the effects of the sputtering. When sputtering with Ar gas, the resputtering due to the ion bombardments produces a film deficient in nitrogen with poor crystallinity. The ion bombardment eventually destroys the crystal structure producing a black amorphous film caused by gallium atoms forming clusters. Alternatively, when sputtering with N2 gas, the activated nitrogen atmosphere enhances nitrogen incorporation and prevents the destruction of the crystal structure, making the film stoichiometric. To obtain high crystallinity, the effect of the self-induced negative bias should be minimized by decreasing the rf power and increasing the total pressure.