5.1 Introduction
5.2 Mathis Model
5.2.1 Application to semipolar GaN
5.3 Misfit dislocation density
5.3.1 Application to AlGaN film on AlN substrate
5.4 Threading dislocation density in heterostructures
5.4.1 Motion of an isolated TD
5.4.2 Reactions among dislocations
5.4.3 Sessile and glissile dislocations
5.4.4 Initial and boundary conditions
5.4.5 GaN/AlN bilayer
5.4.6 GaN-based multilayer
5.5 Summary