Abstract
The invention provides a gallium nitride semiconductor device and a preparation method thereof. The method comprises the steps of employing an extrinsic dopant to form a carbon-doped layer between a buffer layer and a channel layer through an external carbon doping method. The growth conditions of the external carbon doping method are: the surface temperature of a substrate is greater than or equal to 900 DEG C, and the growth pressure is greater than or equal to 50 mbar and the V/III ratio is greater than or equal to 200. The gallium nitride semiconductor device is uniform in carbon concentration and good in breakdown uniformity.