Effects of Mg dopant in Al-composition-graded Al x Ga1−x N (0.45 ≤ x) on vertical electrical conductivity of ultrawide bandgap AlGaN p–n junction

A vertical electrical conductivity of an ultrawide bandgap AlGaN p–n junction with Al-composition-graded AlxGa1−xN (0.45 ≤ x) p-type layer was systematically investigated via experiments and numerical simulation. The experimental results revealed that the initial Al composition of the Al-composition-graded AlGaN should be sufficiently high without Mg dopants to generate enough holes by polarization-induced doping even though the bandgap is higher than that of conventional bulk p-AlGaN. The mechanism behind the vertical conduction is investigated by the simulation, which shows that three-dimensional hole gas formed by the polarization is compensated with electrons generated by unintentionally formed donors.