Surface modification of Cl-adsorbed Si(1 1 1)-7 × 7 by the irradiation of infrared pulsed laser

As the first step to modify a semiconductor surface with light, we have studied the effect of infrared (IR) pulsed laser irradiation on Cl-saturated Si(1 1 1)-7 × 7 surface. After the surface was irradiated by a femto-second IR pulsed laser, we measured temperature programmed desorption (TPD) to observe the change of surface chemical component. Thermal desorption of SiCl2 molecules was reduced and that of SiCl4 molecules was enhanced by the IR irradiation. This result can be interpreted that polychloride radicals made of silicon adatoms are removed from the rest atom and form silicon polychloride clusters on the surface. The change was found to occur in the time scale less than 1 s, so that it may be via an electronic excitation process. Desorption of chlorides under the IR irradiation was detected at room temperature, but not detected at low temperature (150 K). The desorption at room temperature increased during the first 60 s of the IR irradiation, which implies that the desorption is due to a temperature rise of the substrate. It is concluded that the IR irradiation effect on the surface is classified into two processes dominated by the electronic excitation and the thermal effect.