Versetzungen und inverse Pyramidendefekte in AlGaN/GaN-HEMT-Strukturen auf Si und deren Einfluss auf Material- und Bauelementeigenschaften

Description

The GaN on Si material system promises to combine the advantages of a wide bandgap semiconductor with the low manufacturing costs of Si. High Electron mobility transistors based on an AlGaN/GaN heterostructure, for example, can serve as starting point for cost-effective and at the same time very energy-efficient power switches. However, heteroepitaxial fabrication induces high material defect densities, which manifest themselves in particular in the form of dislocations and inverse pyramid defects (V-pits). The influence of these defects on devices is, however, insufficiently known and understood due to the experimentally difficult investigation.

In this work, a structural and electrical characterisation methodology of dislocations and V-pits in GaN on Si was developed and systematically applied to different samples. The focus was on the direct correlation of microstructural and electrical properties while ensuring a statistical relevance of the results. It was possible to identify characteristic dislocation structures and V-pits as leakage current paths through the material and to investigate their occurrence with manufacturing parameters of the samples. It turned out that the latter play an essential role with regard to the electrical activity of dislocations and the occurrence of V-pits. In addition, the findings were examined with regard to their relevance for devices. For the first time, the direct influence of individual, electrically active dislocations in GaN on Si could be revealed. They cause a shift of the turn-on voltage of Schottky diodes to lower values, while V-pits cause a strong degradation of the critical electric field strength of the material. The work thus makes an important contribution to the understanding of the properties and role of these defects and thus to the technological optimisation of the material system.