Investigation on Surface Polarization of Al₂O₃-capped GaN/AlGaN/GaN Heterostructure by Angle-Resolved X-ray...

The surface polarization of Ga-face gallium nitride (GaN) (2 nm)/AlGaN (22 nm)/GaN channel (150 nm)/buffer/Si with Al₂O₃ capping layer is investigated by angle-resolved X-ray photoelectron spectroscopy (ARXPS). It is found that the energy band varies from upward bending to downward bending in the interface region, which is believed to be corresponding to the polarization variation. An interfacial layer is formed between top GaN and Al₂O₃ due to the occurrence of Ga-N bond break and Ga-O bond forming during Al₂O₃ deposition via the atomic layer deposition (ALD). This interfacial layer is believed to eliminate the GaN polarization, thus reducing the polarization-induced negative charges. Furthermore, this interfacial layer plays a key role for the introduction of the positive charges which lead the energy band downward. Finally, a N₂ annealing at 400 °C is observed to enhance the interfacial layer growth thus increasing the density of positive charges.