I had an idea to directly magnetron sputtering ALN thin films on high resistivity GaN substrates. Two-dimensional electron gas was generated at AlN/GaN interface by magnetron sputtering of ALN thin films. I can't find any literature on this kind of experiment. The difficulty lies in the poor quality of the ALN films deposited by magnetron sputtering, which may be difficult to polarize, and the exposure of the Gan substrate to air before sputtering. (GaN substrate is grown by MOCVD) , how the substrate is treated after air exposure makes the sputtering AlN/GaN interface produce two-dimensional electron gas better.