Conductivity type conversion (CTC) describes the process resulting in a p-to-n or n-to-p conductivity change in doped or unintentionally doped mercury cadmium telluride (MCT) materials. The thorough understanding of CTC mechanisms involves the knowledge of diverse fields of electrical science, physics, chemistry and etc.. The related progress to date has been primarily empirical. By summarizing and analyzing some related papers published in recent years, this review describes the MCT/CTC research progress of MCT/CTC with emphasis on ion beam milling techniques.