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

Abstract

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.

Investigation of gap states near conduction band edge in vicinity of interface between Mg-ion-implanted GaN and Al2O3 deposited after ultra-high-pressure annealing

“…The applicable energy range of 0.15-0.45 eV in the bandgap for use of the 1 MHz and 1 kHz C-V curves has been discussed in our previous paper. 30) Briefly, when the measurement frequency is in the range from 1 kHz to 1 MHz, the detection range should be approximately E C -0.15 eV to E C -0.45 eV assuming that the capture cross section is in the range of 1 × 10 -15 -1 × 10 -17 cm -2 . The derived D T distributions are summarized in Fig.…”

“…Actually, a nonuniform doping profile has been derived from the C-V curve for the sample with conventional RTA. 30) Therefore, the high-low-frequency method 33) was used to derive the D T distributions by treating the 1 MHz and 1 kHz C-V curves as the high-and low-frequency limits, respectively. In this method, D T is derived as 33)…”

“…29) Recently, we have found that the E C -0.25 eV level disappeared after conventional rapid thermal annealing (RTA) using a protective AlN cap layer at 1250 °C. 30) However, PAS results showed that the divacancies agglomerated to form large clusters at this temperature rather than being fully recovered by AlN cap annealing at similar temperatures. 24) Although annealing at a higher temperature is necessary, surface damage must be prevented.…”