Si (Silicon) Optical-Grade Single Crystal

Advantages

• Good transmittance from 1.2 to 7.0 μm, with optimal performance in the 3–5 μm mid-wave infrared (MWIR) atmospheric window . Float Zone (FZ) material extends useful transmission to 8–15 μm with reduced absorption at 9 μm.
• High thermal conductivity: 273.3 W/(m·K), enabling efficient heat dissipation in high-power laser and thermal imaging systems.
• Lightweight and cost-effective: Lower density (2.33 g/cm³) than germanium (5.33 g/cm³) and zinc selenide (5.27 g/cm³), offering weight savings for the same aperture at lower material cost.
• High hardness and durability: Knoop hardness of 1150, providing excellent scratch resistance and long service life.
• Opaque in the visible: Completely blocks visible light (transparent only in IR), effectively suppressing stray light interference in infrared systems .
• Mature fabrication technology: Well-established Czochralski (CZ) and Float Zone (FZ) growth methods enable large-diameter windows and lenses at competitive prices .

Typical Specifications

• Chemical formula: Si
• Crystal structure: Face-centered cubic (diamond structure), space group Fd3m
• Transmission range: 1.2–7.0 μm (standard); 1.2–15 μm (FZ, extended)
• Refractive index: 3.41776 @ 10 μm; 3.4223 @ 5 μm; 3.4284 @ 3.5 μm
• Reflection loss: 46.1% @ 10 μm (both surfaces, uncoated)
• Absorption coefficient: 0.01 cm⁻¹ @ 3 μm; 0.03 cm⁻¹ @ 2.6–2.9 μm
• Melting point: 1420°C (1687 K)
• Density: 2.33 g/cm³
• Thermal expansion coefficient: 2.6 × 10⁻⁶/K
• Thermal conductivity: 273.3 W/(m·K)
• Knoop hardness: 1150
• Young’s modulus: 131 GPa
• Poisson‘s ratio: 0.266
• Purity: >99.999% (optical grade); 6N+ for FZ material
• Resistivity: >10 Ω·cm (n-type) or >30 Ω·cm (p-type) for standard optical grade; >100 Ω·cm for FZ
• Orientation: <100> or <111>

Main Applications

• Infrared windows and lenses: Primary application in thermal imaging cameras, FTIR spectrometers, infrared temperature measurement systems, and night-vision devices.
• MWIR optical systems: Lenses and windows for 3–5 μm atmospheric window applications, benefiting from high thermal conductivity and lightweight design.
• Laser mirror substrates: Used as substrates for CO₂ laser mirrors and other infrared laser optics.
• Infrared filters and beam splitters: Substrate material for infrared optical filters and polarizing components.
• Neutron targets: Bulk polished silicon used as neutron targets in physics experiments.
• Terahertz applications: High-resistivity FZ silicon is suitable for THz optical components due to low free-carrier absorption.