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In semiconductor fabrication, etching is one of the major steps, along with photolithography and thin-film deposition. It involves removing unwanted materials from the surface of a wafer using chemical or physical methods. This step is carried out after coating, photolithography, and developing. It is used to remove the exposed thin film material, leaving only the desired portion of the wafer, and then removing the excess photoresist. These steps are repeated numerous times to create complex integrated circuits.

One of the unique properties of semiconductor materials is that their conductivity, as well as their conductivity type (N-type or P-type), can be created and controlled through a process called doping. This involves introducing specialized impurities, known as dopants, into the material to form junctions on the surface of the wafer. The industry employs two main doping techniques: thermal diffusion and ion implantation.

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 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.

C/C composite is a carbon-carbon composite material made of carbon fibers as reinforcement and carbon as matrix through processing and carbonization, with excellent mechanical and high-temperature resistance properties. The material was initially used in aerospace and special fields, and with the maturity of the technology, it has been gradually used in photovoltaic, automotive, lithium battery, medical devices and other fields.