Interface dipole induced threshold voltage shift in the Al2O3/GaN heterostructure

The Al2O3/GaN heterostructure is a crucial component of GaN-based electronic and photonic devices, and the Al2O3/GaN interface quality plays an important role in determining the device performance. Here, using density functional theory, we confirmed that dipole formed at the Al2O3/GaN interface can be attributed to electron transfer and redistribution between Al2O3 and GaN. The formation of dipole was confirmed by X-ray photoemission spectroscopy. The dipole induced electric field at the interfaces of the Al2O3/GaN heterostructures result in negative threshold voltage (VTH) shifts of 2.3 and 1.2 V for the heterostructures without defects and with one Al interstitial (Ali) defect, respectively. On the other hand, the Ali defect can induce positive charges, resulting in negative VTH shifts. Therefore, an improvement in the interface quality (i.e., by eliminating the Ali defect) does not necessarily result in positive VTH shifts. This study reveals novel electronic properties of the Al2O3/GaN heterostructure and offers a path toward the achievement of GaN-based devices with engineered features.