Simulation study on the diversity and characteristics of twin structures in GaN

Abstract

Gallium nitride (GaN) is a promising material for high-frequency and high-power electronics owing to its high thermal stability, wide bandgap, and high breakdown voltage. Monocrystalline GaN films are usually produced by metal organic chemical vapor phase deposition using Si, SiC, or Al 2 O 3 as the substrate. However, the difference in lattice constants and thermal expansion coefficients causes many defects in GaN epilayers . In particular, the formation of twins will strongly influence the electronic properties of GaN-based devices. In this study, the solidification process of GaN was simulated by molecular dynamics at a cooling rate of 10 12 K/s, and the twin structures in GaN were discussed. The results of this simulation showed two types of twins, including coherent twin and rotating twin, which were analyzed by visualization technology. The formation of twins was related to the coexistence of zinc blende and wurtzite phases. Furthermore, the types of twins were closely associated to the stacking ways of zinc blende and wurtzite structures. In general, it is essential to study the microstructure and the structural evolution of twin GaN, in order to give references to experiments about the growth and characteristics of twins. • Zinc blende and wurtzite nucleated randomly and formed lots of complex structures at the beginning of crystallization. • Coherent and rotating twins were formed according to different stacking methods of zinc blende and wurtzite structures. • The rules for the combination of twin structures in GaN crystals have been summarized and it can be generalized. • An error in the stacking sequence can cause the metastable phase c-GaN to start seeding the h-GaN phase.