Improvement of doping efficiency in Mg-Al_0.14Ga_0.86N/GaN superlattices with AlN interlayer by suppressing donor-like defects

We investigate the mechanism for the improvement of p-type doping efficiency in Mg-Al_0.14Ga_0.86N/GaN superlattices (SLs). It is shown that the hole concentration of SLs increases by nearly an order of magnitude, from 1.1× 10¹⁷ to 9.3× 10¹⁷ cm^-3, when an AlN interlayer is inserted to modulate the strains. Schrödinger-Poisson self-consistent calculations suggest that such an increase could be attributed to the reduction of donor-like defects caused by the strain modulation induced by the AlN interlayer. Additionally, the donor-acceptor pair emission exhibits a remarkable decrease in intensity of the cathodoluminescence spectrum for SLs with an AlN interlayer. This supports the theoretical calculations and indicates that, the strain modulation of SLs could be beneficial to the donor-like defect suppression as well as the p-type doping efficiency improvement.