Our group is elucidating various basic properties and dynamics of lattice defects in crystalline materials in order to control defect states for establishing advanced and ultimate functions of materials as Defect Sciences in Solids. Lattice defects, i.e., vacancies/interstitials, impurities, dislocations, stacking faults, their nano-sized complexes, etc., affect crucially the physical properties of semiconductor materials. Thus, the understanding of the structure and nature of such lattice defects is quite essential for improving and developing semiconductor devices. For the purpose, we are (1) characterizing electrical and optical properties and atomistic structure of various defects and complexes and also (2) clarifying their nucleation processes, dynamic modifications and mutual reactions in a wide variety of semiconductors as Si, SiGe, SiC, GaN, ZnSe and so forth. (3) The knowledge is extended to control lattice defect states and furthermore to explore new defect characters for advanced and ultimate functional materials.