Relationship between lattice relaxation and electrical properties in polarization doping of graded AlGaN with high AlN mole fraction on AlGaN template

We investigated polarization doping for hole generation in abrupt and graded GaN/Al 0.7 Ga 0.3 N interfaces on Al 0.99 Ga 0.01 N templates. The abrupt interface exhibited hole generation, whereas the graded interface exhibited electron generation. In the graded Al x Ga 1− x N ( x = 0.65–0), a graded part with an AlN mole fraction ranging from 0.2 to 0 showed a large relaxation. Theoretical estimation revealed that this part contained positive polarization charges, accumulating electrons. Via Mg doping in the graded AlGaN layer, we obtained a high hole concentration of 3 × 10 13 cm −2 . These results indicate that understanding the relaxation conditions in the graded layer is indispensable for polarization doping.