Abstract
We investigated hole concentrations induced by spontaneous and piezoelectric polarization charges in GaN/AlGaN/GaN heterostructures. An AlN mole fraction dependence reveals that the induced hole concentrations were accurately controlled by the AlN mole fractions up to 0.34 in the GaN/AlGaN/GaN structures. We then demonstrated vertical hole conduction across an undoped graded AlGaN layer and hole injection to an active region in a LED structure to some extent. These results suggest that the controlled polarization charges by AlN mole fractions have potential as an alternative doping method for high hole concentrations in nitride semiconductors.