Electrical and structural characterizations of crystallized Al2O3/GaN interfaces formed by in situ metalorganic chemical vapor deposition

Abstract

Al2O3 films were grown in situ by metalorganic chemical vapor deposition at 900 °C on GaN of both Ga- and N-face polarities. High-resolution transmission electron microscopy revealed that the Al2O3 films were crystalline and primarily γ-phase. The Al2O3/Ga-GaN and Al2O3/N-GaN interfaces were both atomically sharp, and the latter further exhibited a biatomic step feature. The corresponding current-voltage (J-V) characteristics were measured on a metal-Al2O3-semiconductor capacitor (MOSCAP) structure. The leakage current was very high when the Al2O3 thickness was comparable with the size of the crystalline defects, but was suppressed to the order of 1 × 10-8 A/cm2 with larger Al2O3 thicknesses. The interface states densities (Dit) were measured on the same MOSCAPs by using combined ultraviolet (UV)-assisted capacitance-voltage (C-V), constant capacitance deep level transient spectroscopy (CC-DLTS), and constant capacitance deep level optical spectroscopy (CC-DLOS) techniques. The average Dit measured by CC-DLTS and CC-DLOS were 6.6 × 1012 and 8.8 × 1012 cm-2 eV-1 for Al2O3/Ga-GaN and 8.6 × 1012 and 8.6 × 1012cm-2 eV-1 for Al2O3/N-GaN, respectively. The possible origins of the positive (negative) polarization compensation charges in Al2O3/Ga-GaN (Al2O3/N-GaN), including the filling of interface states and the existence of structure defects and impurities in the Al2O3 layer, were discussed in accordance with the experimental results and relevant studies in the literature.