Conductive n-type gallium nitride thin films prepared by sputter deposition

Given the recent increase in the demand for gallium nitride (GaN) in different markets like optoelectronics and power devices, the request for epitaxially grown GaN will further increase. To meet this high demand, higher throughput and more economical manufacturing technologies must be advanced. In this work, GaN thin films are deposited by reactive sputter deposition from a liquid gallium target at a substrate temperature of 900 °C. The layers are grown epitaxially on c-plane oriented sapphire in an industrial-scale sputter tool from Evatec AG. Due to the growth rate of >1 nm/s and the fast substrate heat-up time, the throughput in a production setup can be increased compared to other GaN growth techniques. The resistivity of the intrinsic insulating GaN can be lowered by intentional Si doping during the sputter deposition process by three orders of magnitude. Thereby, conductive n-type GaN can be grown with different dopant amounts. The carrier mobility of the sputter deposited film is 45 cm2 V-1 s-1 at a carrier concentration of 1.1 × 1020 cm-3 based on room temperature Hall measurements using a van der Pauw geometry. The lowest resistivity reaches 1300 μω cm, which is confirmed by sheet resistance measurements. Undoped films exhibit an x-ray diffraction rocking curve full width at half maximum of 0.2°, which increases up to 0.5° for highly Si-doped layers. The presented results show that GaN prepared by reactive sputter deposition from a liquid gallium source is a viable alternative to conventional deposition techniques for GaN.