Studies on surface texturing by chemically enhanced laser ablation in a variety of materials, particularly silicon and
germanium are reported. The materials are exposed either to femtosecond or nanosecond laser irradiation in a variety
of vacuum or gaseous environments including air, He, sulfur hexafluoride (SF6) or hydrogen chloride (HCl). The
dynamics of pillar formation are elucidated and it is shown that the mechanisms are very different in these two pulse
length regimes. Surface texturing responds to the combined effects of laser assisted chemical etching and laser
ablation. Various processing steps either before or after laser irradiation allow us to modify the nature of the pillars
that are formed. In this way we can make ordered arrays that extend over ≥1 cm2 in just a few minutes of laser
exposure. Post-laser processing wet etching can produce Si pillars that are over 50 &mgr;m long with tips that are only 10
nm across as well as macroporous silicon with crystallographically defined pores. A process we call solidification
driven extrusion creates nanoscale spikes atop the pillars under certain circumstances - a process that is more
prevalent for Ge than Si. Pillar-covered surfaces of Si and Ge are black; that is, they exhibit very low reflectivity. For
Si this low reflectivity extends to wavelengths far below the band gap raising the possibility that we may be able to
make other transparent materials highly absorptive by laser texturing.
Results of semiconductor laser crystallization of a-Si:H on transparent conducting fluoride doped tin oxide coated glass are discussed. A-Si:H films were prepared by plasma enhanced chemical vapor deposition. Laser crystallized films of a-Si:H were characterized by X-ray diffraction and optical microscopy. Semiconductor laser crystallization process as compared to well-established excimer laser offers low cost large area technology for solar cell, display and other applications. Longer wavelength of diode lasers (805 nm) allows light to penetrate deeper in the films for crystallization of thicker films required for enhanced light absorption.
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