Nanopatterning of Silicon Carbide by UV and Visible Lasers.

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Nanopatterning of Silicon Carbide by UV and
Visible Lasers.

• By
• Arvind Battula
• 12/02/2004

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Properties of SiC.

• Wide-gap semiconductor.
• High thermal conductivity.
• Low thermal expansion coefficient.
• High melting point.
• High hardness.
• High breakdown electric field.
• High electron saturation.
• Suitable for high temperature, power and
  frequency applications.

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Photetching of SiC by VUV-266nm Multiwavelength.
Zhang, et. Al., 1996, Direct photoetching of
single crystal SiC by VUV-266 nm multiwavelength
laser ablation, Appl. Phys. A,64, p.367.
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Femtosecond Pulsed Laser Induced 3C/SiC surface
Morphology.
Pulse duration 120 fs wavelength 800 nm
Dong.Y., and Molian. P., 2003, Femtosecond
pulsed laser ablation of 3C-SiC thin film on
Silicon, Appl. Phys. A, 77, p. 839
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Monolayer of SiO2 Nano-spheres on SiC.
SEM micrograph of the monolayer of silica spheres
diameters (a) 1.76 µm and (b) 640 nm.
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Experimental Setup.
Schematic of (a) experimental setup, (b)
Irradiation of the spheres on SiC.
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? 532 nm, 640 nm Silica Spheres, 400 nm SiC
film.
525 mJ/cm2
425 mJ/cm2
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? 532 nm, 1.76 µm Silica Spheres, 400 nm SiC
film.
200 mJ/cm2
275 mJ/cm2
325 mJ/cm2
400 mJ/cm2
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? 355 nm, 640 nm Silica Spheres, 400 nm SiC
film.
400 mJ/cm2
300 mJ/cm2
500 mJ/cm2
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? 355 nm, 1.76 µm Silica Spheres, 400 nm SiC
film
225 mJ/cm2
175 mJ/cm2
350 mJ/cm2
225 mJ/cm2
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Gradual Changes in the Melting Zone of one Laser
Spot.
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? 532 nm, 250 nm Gold Spheres, 300 mJ/cm2 , 200
nm SiC film.
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? 355 nm, 250 nm Gold Spheres, 425 mJ/cm2 , 200
nm SiC film.
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Features for 355 nm Laser on Bulk SiC.
Features formed on the SiC substrate with a 355
nm laser (a) 1.76 µm diameter spheres and 950
mJ/cm2 and (b) 640 nm diameter spheres and 850
mJ/cm2.
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AFM Results for 355 nm Laser.
Variation in the feature size with respect to the
laser intensity for 355 nm laser and 1.76 µm
spheres.
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Features for 532 nm Laser on Bulk SiC.
Features formed on the SiC substrate with a 532
nm laser (a) 1.76 µm diameter spheres and 2
J/cm2 and (b) 640 nm diameter spheres and 6 J/cm2.
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AFM Results for 532 nm Laser.
AFM cross section view of the features obtained
with 532 nm laser and 1.76 µm spheres.
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Ablation Mechanism.

• At low laser fluence the formation of
  laser-induced nanostructures are from
  defect-activation.
• The pre-existing defects facilitate local
  absorption of incident laser.
• This results crystalline SiC to lattice disorder
  due to electronic excitation.
• Weakens interatomic bonding and thus lower the
  vibrational energy required for lattice disorder.
• With increasing laser-induced lattice defects,
  the formation of grain boundries results in
  polycrystallization of SiC film.

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Non-Thermal Transitions in Semiconductors.
S.K. Sundaram and E. Mazur, Inducing and Probing
Non-Thermal Transitions in Semiconductors Using
Femtosecond Laser Pulses, Nature Materials, 1,
217-224 (2002).