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The growth of GaN epitaxy on GaN substrate presents a unique challenge, despite the material’s superior properties when compared to silicon. GaN epitaxy offers significant advantages in terms of band gap width, thermal conductivity, and breakdown electric field over silicon-based materials. This makes the adoption of GaN as the backbone for the third generation of semiconductors, which provide enhanced cooling, lower conduction loss, and improved performance under high temperatures and frequencies, a promising and crucial advancement for the photonic and micro-electronic industries.

Defect-free epitaxial growth occurs when one crystal lattice has nearly identical lattice constants to another. Growth happens when lattice sites of the two lattices at the interface region are approximately matched, which is possible with a small lattice mismatch (less than 0.1%). This approximate matching is achieved even with elastic strain at the interface, where each atom is slightly displaced from its original position in the boundary layer. While a small amount of strain is tolerable for thin layers and even desirable for quantum well lasers, the strain energy stored in the crystal is generally lowered by the formation of misfit dislocations, which involve a missing row of atoms in one lattice.

The first generation of semiconductor materials is mainly represented by silicon (Si) and germanium (Ge), which began to rise in the 1950s. Germanium was dominant in the early days and was mainly used in low-voltage, low-frequency, medium-power transistors and photodetectors, but due to its poor high temperature resistance and radiation resistance, it was gradually replaced by silicon devices in the late 1960s. Silicon is still the main semiconductor material in the field of microelectronics due to its high technological maturity and cost advantages.

Silicon carbide (SiC) is highly favored in the semiconductor industry for its excellent physical and chemical properties. However, the high hardness and brittleness of SiC pose considerable challenges to its processing.

Before discussing the Chemical Vapor Deposition (CVD) silicon carbide (Sic) process technology, let's first review some basic knowledge about "chemical vapor deposition." Chemical Vapor Deposition (CVD) is a commonly used technique for preparing various coatings. It involves depositing gaseous reactants onto a substrate surface under appropriate reaction conditions to form a uniform thin film or coating.