Atom probe tomography studies of Al₂O₃ gate dielectrics on GaN

Atom probe tomography was used to achieve three-dimensional characterization of in situ Al₂O₃/GaN structures grown by metal organic chemical vapor deposition (MOCVD). Al₂O₃ dielectrics grown at three different temperatures of 700, 900, and 1000°C were analyzed and compared. A low temperature GaN cap layer grown atop Al₂O₃ enabled a high success rate in the atom probe experiments. The Al₂O₃/GaN interfaces were found to be intermixed with Ga, N, and O over the distance of a few nm. Impurity measurements data showed that the 1000°C sample contains higher amounts of C (4×10¹⁹/cm³) and lower amounts of H (7×10¹⁹/cm³), whereas the 700°C sample exhibits lower C impurities (<10¹⁷/cm³) and higher H incorporation (2.2×10²⁰/cm³). On comparing with Al₂O₃ grown by atomic layer deposition (ALD), it was found that the MOCVD Al₂O₃/GaN interface is comparatively abrupt. Scanning transmission electron microscopy data showed that the 900°C and 1000°C MOCVD films exhibit polycrystalline nature, while the ALD films were found to be amorphous.