2. Heteroepitaxy of III-N materials

2.1 Substrates used

The choice of substrate is crucial to the quality of heteroepitaxy. III-N materials can be grown on a variety of substrates. Ideally, gallium nitride should be grown directly on a bulk GaN substrate, in order to reduce structural defects: this is known as homomorphic growth. However, for most applications, the nature of the host substrate is different from that of the epitaxial layer. This is referred to as metamorphic growth, because in the case of GaN, there is no lattice-tuned substrate.

In industry, the value of the dislocation density is one of the most important criteria for the development of reliable devices. For the manufacture of HEMT-type structures, substrates must combine high crystalline quality and good electrical insulation,...