EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In this study we investigated the interfacial adhesion behaviour of GaN/AlN heterostructures grown on sapphire and Si substrates by cross-sectional nanoindentation (CSN) and four-point bending (4PB) tests. Particularly, the influence of the AlN buffer layers, necessary for GaN growth on Si, on the delamination response is determined. Analytical models based on beam- and elastic plate theory have been applied respectively to calculate the interfacial critical energy-release rate (Gic) with both methods, which are found to be in good agreement, provided the loading conditions are similar. Detailed microstructural investigations of the relevant interfaces using transmission and scanning electron microscopy are also presented. Theoretically, it is assumed that delamination in a multilayer stack generally occurs at the interface with the lowest adhesion strength. To gain further insight into the interactions of a crack approaching an interface, we applied a fracture mechanics based method on the GaN/AlN/Si stack. This allows to estimate a lower boundary of the energy-release rate of the GaN/AlN interface. In this approach the competition between crack deflection along the interface and penetration of the subsequent material is solved analytically. We could prove that considering our geometry and material properties delamination along the AlN/Si interface is indeed expected. Comparison to the fracture toughness of AlN also shows that by increasing the adhesion strength even by a small amount, fracturing of the AlN layer may become more preferential.
The findings of this study contribute to a better understanding of the adhesion properties of III-N semiconductors, which are of high technological relevance. Especially in the case of the GaN/AlN/Si stack, for which to our knowledge experimental values of the energy-release rate are not available.