Characterization of band bendings on Ga-face and N-face GaN films grown by metalorganic chemical-vapor deposition

The change of band banding with the crystal polarity of GaN films was investigated using high-resolution photoemission spectroscopy. Compared with a N-face sample, the Ga-face sample exhibited higher Schottky barrier height and lower contact resistivity of a Ti/Al-based Ohmic contact. It was found that Ga-face GaN has a larger surface band bending than N-face GaN by 1.4 eV due to spontaneous polarization, resulting in higher Schottky barrier height. The lower Ohmic contact resistivity on Ga-face GaN originated from the formation of polarization-induced two-dimensional electron gas at the interface of AlN with GaN.