No abstract

Recent experiments suggest that Mg condensation at threading dislocations induces current leakage, leading to degradation of GaN-based power devices. To investigate this, we perform first-principles total-energy electronic-structure calculations for various Mg and dislocation complexes. We find that threading screw dislocations (TSDs) indeed attract Mg impurities, and that the electronic levels in the energy gap induced by the dislocations are elevated toward the conduction band as the Mg impurity approaches the dislocation line, indicating that the Mg-TSD complex is a donor. The formation of the Mg-TSD complex is unequivocally evidenced by atom probe tomography in which Mg condensation around the [0001] screw dislocation is observed in a p–n diode. These findings provide a picture in which the Mg, being a p-type impurity in GaN, diffuses toward the TSD and then locally forms an n-type region. The appearance of this region along the TSD results in local formation of an n–n junction and leads to an increase in the reverse leakage current.

Our message is oxidation process must be minimized as possible. Many carbon-related defect structures are reported in SiC/SiO2 interface. In this paper, we investigated the effect of oxidation to the defect forming by density functional theory (DFT). In the result, we found carbon defect structure that completely different from in the present report. This defect structure has carbon-carbon single bond with no dangling bond. To see the forming process, compressive strain from inserted oxygen atoms induce the rearrangement of structure and cause C-C defect structure. We can know that this structure is formed with energy gain about 3.8eV. And this C-C defect induces trap state under the conduction bottoms.

We demonstrate on the basis of first-principles calculations that the formation of carbonate-like moiety in SiO2 could be the intrinsic origin of negative fixed charge in SiC thermal oxidation. We find that two possible origins for the negative fixed charges are O-lone-pair state and a negatively charged CO3 ion in SiO2. Such CO3 ion is able to be formed as a result of the existence of residual C atoms in SiO2, which are expected to be emitted from the interface between SiC and SiO2, and the incorporation of H atoms during wet oxidation.

We performed first-principle calculations to investigate the effect of incorporation of N atoms into Al2O3 gate dielectrics. Our calculations show that the defect levels generated by VO in Al2O3 are the origin of the stress-induced gate leakage current and that VOVAl complexes in Al2O3 cause negative fixed charge. We revealed that the incorporation of N atoms into Al2O3 eliminates the VO defect levels, reducing the stress-induced gate leakage current. Moreover, this suppresses the formation of negatively charged VOVAl complexes. Therefore, AlON can reduce both stress-induced gate leakage current and negative fixed charge in wide-bandgap-semiconductor MOSFETs.