Abstract: Doping and defects controls are life blood in semiconductor device physics to effectively enhance the device properties. Tuning the dopants and defects is possible by changing the mechanical or electronic environment of the lattice. In this talk, I’ll present my recent research results of different defect controlling techniques using first principles density functional theory method. We found that external strains can be effective strategies to tune dopant formations, dopant sites and intrinsic defects formation and defects types in various semiconductor systems. Dual surfactant (elements that always stay on top of the growth surface) enhanced p-type doping will also be presented.