Optical Hyperdoping

As discussed in the previous chapters, ion implantation followed by pulsed laser melting is a well-studied process for achieving localized heavy doping in semiconductors, where the dopant concentration can exceed the equilibrium solid solubility limit by orders of magnitude. In addition to the useful electrical properties exhibited by semiconductors hyperdoped with p- and n-type dopants, novel material properties have also been observed over the recent years in single-crystalline semiconductors containing a nonequilibrium concentration of various nondopant impurities. In this chapter, we focus on the intentional introduction of impurities into semiconductors as a method to modify their electronic band structure and, therefore, optical properties, a process which has recently become known as "optical hyperdoping." The research effort in optical hyperdoping has almost exclusively focused on Si and most of this chapter is dedicated to reviewing the literature on optical hyperdoping in Si. However, there has been an emerging work on hyperdoped Ge which we summarize. In addition, a logical extension of the Ge work to dilute GeSn alloys, also formed by implantation and pulsed laser melting, has received attention recently and a brief overview of this body of research is provided.