Method for preparing magnesium-doped semiconductor film and semiconductor film thereof

The embodiment of the invention discloses a method for preparing a magnesium-doped semiconductor film. The method comprises the steps of: acquiring a substrate material; forming a GaN layer on the substrate material; and forming a magnesium-doped AlGaN layer on the GaN layer and enabling the content of aluminum in the AlGaN layer to subject to linear change from a part close to the GaN layer to a part far away from the GaN layer. According to the embodiment of the invention, the AlGaN layer with changing aluminum content is formed on GaN which is not doped intentionally, and simultaneously trace magnesium elements are doped. Because the self-polarization effect and the polarization intensity of AlN and GaN change regularly, a built-in electric field is formed in the AlGaN layer; the built-in electric field repels negative carriers and attracts positive carriers, so that free holes are induced to concentrate in the AlGaN layer, thus, the concentration of the negative carriers is increased, and the doping effic