Nanostructuring in Indirect Band-gap Semiconductor Using IR Femtosecond Double Pulses

Periodic nanostructures inside an indirect band-gap semiconductor crystal have been induced by a focused beam of a femtosecond double-pulse. Such self-organized nanostructures in silicon are composed of strained silicon, which exhibit a high electric conductivity. On the other hand, the nanostructures have not been empirically formed in a direct band-gap semiconductor. We classify the observed phenomenon into two types based on the bandgap structure and propose the mechanism for nanostructuring. Since the scattering of phonons by the nanostructure in semiconductor leads to a low thermal conductivity, we have also proposed the possible application to the thermoelectric conversion devices.