Three-dimensional hole gas induced by polarization in (0001)-oriented metal-face III-nitride structure

Polarization-doping via graded AlGaN layer on N-face $(0001¯)$ GaN has been demonstrated as an inspiring p-type doping method for wide-band-gap nitrides. However, the polarity of III-nitrides grown by metal organic chemical vapor deposition is metal-face typically. In this paper, we show that three-dimensional mobile hole gas induced by polarization can be formed in (0001)-oriented metal-face III-nitride structure. The hole concentration of a Mg-doped $AlxGa1−xN$ layer with graded Al composition from $x=0.3$ to 0 grown on AlN buffer layer is remarkably enhanced, compared with that of a Mg-doped GaN layer grown under the same conditions. In addition, the hole concentration in the graded AlGaN layer is absence of freezeout as the temperature decreases, indicating that the hole is induced by polarization. This p-type doping method paves a way for achieving high-efficiency in wide-band-gap semiconductor light-emitting devices with p-type doping problem.