Both ZnO and SIC are wide band gap (Eg ≳ 3-eV) semiconductors (ρ ~ 1 Ω-cm) having relatively high melting points (~2000 and ~2700°C for ZnO and SiC, respectively). However, both are volatile and sublime at lower temperatures (~1700 and ~2000 and ~2700°C for ZnO and SiC, respectively). In pure form, ZnO and SiC are transparent in the visible and thus are not candidates for pulsed laser processing (PLP) with visible or near-IR lasers. However, both absorb strongly (α ≈ 105 cm−1) in the near UV, and both have reststrahlen absorption bands near 10 μm (α ≈ 102 and 104 cm−1 for ZnO and SiC, respectively). Thus both excimer and CO2 lasers are potentially useful for PLP of ZnO and SiC. Moreover, the coupling of laser radiation to these materials is fundamentally different for CO2 and excimer lasers: UV radiation couples to the electronic system via transitions across the band gap, while CO2 radiation couples directly into the crystal lattice.
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