The effect of periodic delta-doping and modulation-doping on high Al content n-AlxGa1-xN （x = 0.55） epilayers grown by MOCVD has been investigated. Measured by XRD, AFM, contactless sheet resistance, and Hall-effect tests, 8-doped and modulation-doped n-Alx Ga1-xN have better crystal quality, surface morphology and electrical properties as compared with uniformly-doped n-AlxGa1-xN. These improvements are attributed to the SiNx growth mask induced by δ-doping layers and the dislocation-blocking effect induced by both growth techniques. In addition, due to the broadened doping profile ascribed to enhanced dopant diffusion at high growth temperatures （1150 ℃） ofn-Al0.55 Ga0.45N, modulation-doped n-Al0.55 Ga0.45N has similar properties as 8-doped n-Al0.55 Ga0.45N.
