ABSTRACT
Silicon carbide (SiC) is well known for showing polytypes of various stacking sequences with the same chemical composition, probably owing to the low formation energy of stacking faults. The polytypes are expressed by the number of Si-C layers in the unit cell together with the symbol of crystal systems (C for cubic, H for hexagonal, and R for rhombohedral). Among many polytypes, technologically important ones are 3C-, 4H-, and 6H-SiC. In general, 3C-SiC is known as a low-temperature polytype, and 4H-and 6H-SiC are high-temperature polytypes. The wide band gaps of SiC give a very high breakdown field, about 10 times higher than that of Si or GaAs [1]. Optical phonons of high energy, as high as 100-120 meV [2], due to strong Si-C bonding, lead to a high electron-saturation drift velocity (2×107 cm/s in 6H-SiC) [3] and a high thermal conductivity (4.9 W/K cm) [4]. Controlled n-and p-type doping can be done during crystal growth, and selective doping of both donor-and acceptor-type impurities can be carried out by ion implantation. Besides, SiC is the only compound semiconductor that can be thermally oxidized to form high-quality SiO2. These outstanding properties give SiC great potential for high-power, high-frequency/high-power, high-temperature, and radiation-resistant devices, which cannot be realized with Si or GaAs. Particularly, a theoretical simulation has predicted that SiC-powered electronic devices will overtake present-day Si devices on account of extremely low power dissipation and reduced chip sizes [5].
