Acceptor traps as the source of holes in p-type N-polar GaN/(AlN/AlGaN) superlattices

This study experimentally shows the existence of acceptor traps at positive polarization interfaces (PPIs) acting as the source of holes in N-polar p-type modulation doped GaN/(AlN/AlGaN) superlattices (SLs) with low Mg doping. The observation of measured hole concentration higher than the dopants (here, Mg) put in the samples during growth can be explained by the ionization of acceptor traps, which are placed 0.8 eV above the valence band of GaN at the PPI. All samples were epitaxially grown using metal organic chemical vapor deposition and were characterized using x-ray diffraction and room-temperature Hall measurements. The measured hole concentrations are compared against calculated values from STR FETIe, and the measured mobility trends are explained using the separation of the positive polarization interfaces from the two-dimensional hole gas in the systems, strengthening the hypothesis. A second study is also presented where acceptor traps were ionized in a p-type modulation doped GaN/AlGaN SL without an AlN layer-by keeping the superlattice period thickness constant and increasing the AlGaN composition. Following the hypothesis of the existence of an acceptor trap, these experimental studies demonstrate the charge-balance in systems that show p-type behavior without sufficient doping. Published under an exclusive license by AIP Publishing.

Automated summary

This study experimentally demonstrates the existence of acceptor traps acting as the source of holes in N-polar p-type modulation doped GaN/(AlN/AlGaN) superlattices. The ionization of acceptor traps explains the higher measured hole concentration compared to the dopants used during growth. The study also provides evidence for the charge-balance in systems showing p-type behavior without sufficient doping.