Laser surface texturing has been achieved using lasers with pulse
widths in the nanosecond and femtosecond regime [11,34,35].
Depending on the pulse width, wavelength and laser fluence, surface
texturing is obtained either by (a) ablation-induced surface grooving
[10,34] or (b) laser-induced self-assembled semi-periodic light
trapping structures [29,36–38]. The ablation-induced surface
grooving technique creates 50 mm deep craters to reduce reflection
losses with significant material lost during etching of the
laser-damaged region. Short wavelength (l¼248 and 532 nm)
nanosecond laser irradiation can create self-assembled conical
pillars that very effectively trap light, but the height of these pillars
are over 20 mm. This makes the process unsuitable for nextgeneration
ultrathin wafers, where the texture size approaches the
thickness of the wafer. Ultrafast (fs and ps) lasers on the other hand
are able to create similar conical structures that are about 3–10 mm
high with similar light trapping properties [39–41]. The high density
or decreased periodicity of these structures relaxes the pillar height
thus providing excellent light trapping. The other advantage of
ultrafast laser (femtosecond pulses) over pulsed (nanosecond
pulses) laser processing is that the heat-affected zone and
laser-induced damage can be greatly minimized [40]. Hence,
ultrafast laser processing is seen to be a very promising technology
for surface texturing.
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