Interface state density distribution near conduction band edge at Al₂O₃/Mg-ion-implanted GaN interface formed after activation annealing using AlN cap layer

An interface state density ( D it) distribution near the conduction band edge ( E C) at the Al2O3/Mg-ion-implanted GaN interface was measured after ion implantation, annealing with an AlN protective cap, and cap layer removal. Mg ions were implanted into n-GaN with a Si concentration of 6 × 1017 cm−3 at a maximum Mg concentration of 2 × 1017 cm−3, resulting in the maintenance of the n-type conduction in GaN even after the activation of Mg dopants. Activation annealing was carried out at 1250 °C for 1 min using an AlN cap layer. The complete removal of the AlN cap layer was accomplished by wet etching, which was confirmed by x-ray photoelectron spectroscopy. The photoluminescence spectrum showed donor–acceptor-pair emission after annealing, indicating the activation of Mg acceptors. By applying the capacitance–voltage method to a completed metal–oxide–semiconductor diode, we derived a continuous distribution of relatively low D it below 5 × 1012 cm−2 eV−1, which increased monotonically toward E C in the range from E C − 0.15 to E C − 0.45 eV. Compared with the D it distribution of the as-implanted sample, the density of the discrete level at E C − 0.25 eV generated by divacancies markedly decreased upon 1250 °C annealing.