The plasma or free-carrier state in a semiconductor has received considerable attention in the past, owing to its applications in microwave control components. Essentially, both the dielectric and conductive properties of the plasma in a semiconductor can be used to control the transmission and propagation of an electromagnetic wave. Optical carrier injection can be achieved easily by single photon absorption if the photon energy is larger than the band gap energy of the material. The phenomenon that causes the transformation of material property is referred to as the photoconductivity effect. A photoconductivity effect that is initiated by ultrashort optical pulses is referred to as the ultrafast photoconductivity effect [1].