Simulation supported analysis of the effect of SiNx interlayers in AlGaN on the dislocation density reduction

In the last few years aluminium nitride (AlN) has attracted much attention due to its extremely large direct band gap of approximately 6.0 eV and its impressive chemical and thermal stability. Thus AlN and AlxGa1-xN ternary alloys are promising materials for high-power high temperature electronic applications and optoelectronic devices in UV range. For group-III nitride wafers are still not available in sufficient amount and quality, AlN has to be grown on foreign substrates such as Al2O3 (Sapphire). Unfortunately the large lattice mismatch between the AlGaN/Al2O3 interface of up to -14% leads to the formation of threading dislocations (TD), inducing a high dislocation density in the range of 10cm and decreasing the crystal quality [1, 2]. Thus it is still a big challenge to grow AlGaN directly on foreign substrates with small dislocation density. As is already known, SiN interlayers can act as anti-surfactants and drastically reduce the dislocation density in pure GaN layers [3, 4]. In our work we could observe a very efficient dislocation annihilation of the a-type TDs at the SiN interlayer even in AlxGa1-xN layers with relatively high Al content of x=0.2.