What is pyrolytic graphite?

Abstract: Pyrolytic graphite (PG) is an advanced carbon material synthesized by high-temperature pyrolysis of hydrocarbon gas (usually 1800-3000°C). Compared with other carbon materials, pyrolytic graphite (PG) has many excellent physical properties and is widely used as epitaxial growth base, thermal field components and PG graphite crucible in semiconductor crystal growth.

What is Pyrolytic Graphite?

Pyrolytic graphite (PG) is an advanced carbon material synthesized by pyrolysis of hydrocarbon gases at high temperatures (typically 1800-3000°C) with a unique layered structure. Unlike natural graphite with its geological formation process and disordered crystal arrangement, pyrolytic graphite exhibits highly ordered anisotropic properties through artificial modulation. Its structure consists of stacked graphene layers arranged strictly perpendicular to the deposition direction, resulting in significant orientation-dependent features:

Core Properties

1. Anisotropy:

1) In-plane orientation (parallel graphite layers):

Ultra-high thermal conductivity (up to 1950 W/m-K, more than copper)

High electrical conductivity and mechanical strength

2) Out-of-face direction (perpendicular graphite layer):

Extremely low thermal/electrical conductivity, exhibits insulating properties

Brittle texture, easy to disintegrate along the layers

2. Structural perfection:

Highest quality highly oriented pyrolytic graphite (HOPG) achieves near-perfect graphene layer orientation alignment by chemical vapor deposition (CVD) and subsequent annealing treatment

3. Thermally stable and chemically inert:

Oxidation resistant up to 600°C in air

Resistant to extreme thermal shock

Inert in most chemical environments

Differences with other carbon materials

1. Pyrolytic Carbon:

A generic term for pyrolytically deposited carbon materials, Pyrolytic Carbon (PyC) is a synthetic carbon material prepared by Chemical Vapor Deposition (CVD) or pyrolysis of hydrocarbons (e.g. methane, propane). Unlike graphite, the structure of pyrolytic carbon can be amorphous (glassy carbon) or partially graphitized, depending on the preparation temperature and post-treatment process.

2. Natural Graphite:

Naturally occurring, less pure, does not possess the anisotropy of PG.

3. Highly Oriented Pyrolytic Graphite (HOPG):

Highly Oriented Pyrolytic Graphite (HOPG) is the top form of Pyrolytic Graphite (PG), which has a perfect layered structure close to a single crystal and a very high degree of crystalline orientation. Typically, HOPG is a synthetic graphite prepared by high-temperature chemical vapor deposition (CVD) combined with ultra-high-temperature annealing (>3000°C), and its graphene layers (002 crystalline planes) have an orientation deviation angle of <1°.

What are the specific applications of pyrolytic graphite in semiconductor crystal growth?

Pyrolytic Graphite (PG) plays a key role in the semiconductor crystal growth process due to its unique anisotropy, ultra-high purity and high temperature stability. The following are its specific applications:

1. Epitaxial Growth Substrates

In the silicon carbide (SiC) epitaxy process, PG pedestals reduce stress defects due to their low coefficient of thermal expansion (4.2×10-⁶ K-¹) matching the SiC lattice. For example, SGL Carbon's SiC-coated PG substrates minimize wavelength deviation and improve LED chip yields.

2.Crucible and Hot Field Components

Thermal Field Insulation: Reflectors and heat shields made of PG (e.g. SIGRAFLEX® graphite foils) achieve a uniform thermal field distribution through high in-plane thermal conductivity (220 W/mK), which improves crystal quality.

Pyrolytic Graphite coated Crucible: For the growth of semiconductor crystals such as silicon (Si), silicon carbide (SiC), etc. They are temperature-resistant up to 3000°C and are chemically inert and surface-dense to avoid melt contamination. For example, in the CZ method of monocrystalline silicon growth, PG-coated graphite crucibles are resistant to erosion by the silicon melt.