Dislocation-Based Thermodynamic Models of V-Pits Formation and Strain Relaxation in InGaN/GaN Epilayers on Si Substrates

摘要

The strain relaxation mechanism in Ⅲ-N materials is occurred through the motion of dislocations that generated at Ⅲ-N/Si interface as a result of large mismatch in lattice and thermal expansion coefficients. As a result of the large lattice mismatch between different layers, the upper layer gets strained and with thicker layers, the strain energy increases until a thickness limit called the critical material thickness. Most of such dislocations (threading dislocations) penetrate the top surface forming Ⅴ-pits defects at the top surface that relax the material. These Ⅴ-pits directly affect the device efficiency, performance, and reliability. Therefore, in this paper, a thermodynamics-based model will be used to study the Ⅴ-pits formulation and growth in the Ⅲ-N (especially, InGaN-based materials). In this model, three types of energies are used under a balanced system to model the Ⅴ-pit formation and growth. These energies are the strain energy in the InGaN epilayer, the destruction energy as a result of dislocation to form the Ⅴ-pit, and the strain energy of the Ⅴ-pits facets that generated during the facet nucleation.