Interfacial band parameters of ultrathin ALD–Al₂O₃, ALD–HfO₂, and PEALD–AlN/ALD–Al₂O₃ on c-plane, Ga-face GaN through XPS measurements

Ultrathin oxides (UOs) and ultrathin nitrides (UNs) play a crucial role in forming lattice-mismatched semiconductor heterostructures that are fabricated by using semiconducting grafting approach. The grafting approach has shown its great potential to realize GaN-based heterojunction bipolar transistors by fulfilling the missing high-performance p-type nitrides with other p-type semiconductors. A handful of UO and UN dielectrics readily available by atomic layer deposition (ALD) satisfy the requirements of double-sided surface passivation and quantum tunneling for semiconductor grafting. Due to the states existing between the UO or UN conduction band and that of the GaN, the ALD deposited UO or UN layer can generate significant effects on the surface band-bending of GaN. Understanding the band parameters of the interface between UO or UN and c-plane Ga-face GaN can guide the selection of interfacial dielectrics for grafted GaN-based devices. In this study, we performed x-ray photoelectron spectroscopy measurements to obtain the band-bending properties on c-plane, Ga-face GaN samples coated by different ALD cycles of ultrathin-HfO2 or ultrathin AlN. The valence band spectra of GaN coated with ultrathin-ALD–Al2O3, ALD–HfO2, or PEALD–AlN/ALD–Al2O3 were further analyzed to calculate the valence and conduction band offsets between the ALD dielectrics and the Ga-face GaN under different thicknesses and post-deposition annealing conditions of the dielectrics.