Fabrication of photo-induced microstructure embedded inside ZnO crystal

摘要

In this paper, micromachining inside of direct and indirect semiconductor, such as zinc oxide crystal (ZnO) and single-crystalline silicon(c-Si) using femtosecond laser pulses is successfully demonstrated. In the case of ZnO, oxygen vacancy or interstitial zinc was three-dimensionally induced by the near-infrared femtosecond laser pulse irradiation. The threshold energy for oxygen defect formation increased with increasing in a pulse width. The mechanism of the pulse-width dependence of the damage threshold inside ZnO could be interpreted in terms of the excitonic Mott transition to the electron-hole plasma which depends on the electron plasma density induced by the laser irradiation. We have also successfully micromachined inside c-Si using infrared ultrashort laser pulses (λ = 1.24 μm). Optical microscope observation under an infrared lamp illumination indicates low density material or scattering structure was formed in the vicinity of the focal spot.