Analysis and Evaluation Technologies
Atomic-level analysis of internal defects contributing to the improvement of volume resistivity in magnesia-doped aluminum nitride
It has been reported that aluminum nitride (AlN) possesses high volume resistivity, and that the addition of magnesium oxide (MgO) further improves this property in high-temperature ranges. It has been proposed that this improvement is related to internal defects known as inversion domain boundaries (IDB), but the detailed mechanism had remained unclear. Therefore, we clarified the origin of this improvement in volume resistivity from the perspective of the atomic and electronic structures of the IDB.
From the scanning transmission electron microscope (STEM) image in the left figure (①), it can be seen that the addition of magnesium oxide to aluminum nitride generates linear defects. The leftmost image in the right figure (②) shows the structure of this defect region obtained by atomic-resolution annular bright-field scanning transmission electron microscopy (ABF STEM). This defect appears at the boundary where the polarities of the aluminum nitride crystals (top and bottom) are inverted, and as shown by the STEM-EDS mapping images (the four color images) in the right figure (②), oxygen and magnesium are respectively segregated into layers. When first-principles calculations were performed based on the structural model obtained from this atomic-level analysis, it was suggested that this defect acts as a potential barrier, inhibiting electron conduction and thereby improving the volume resistivity.
