Ion beam synthesis of (Si_(1-x)C_(1-y))Ge_(x+y) solid solutions in 4H-SiC

摘要

Silicon Carbide is a wide band gap semiconductor material that offers many advantages over conventional semiconductor materials. Because of the high saturation drift velocity, the high break down field, the high thermal conductivity and chemical and radiation resistivity this material is suitable for electronic devices, operating at high temperatures, high frequencies and harsh environments. For the realization of many devices such as HBT (heterobipolar-transistor) and HEMT (high electron mobility transistor), the heterostrucrure formation is assumed. Up to date the only intrinsic heterostructures based on SiC are β-SiC/α-SiC heterojunctions using different bandgaps of different polytypes. Unfortunately this kind of heterostructures is not commercialized because of unsolved technological problems. For this reason the creation of (Si_(1-x) C_(1-y))Ge_(x+y) semiconductor solid solutions is attractive for bandgap and strain engineering in the Silicon Carbide technology. This new material is a suitable alternative to the aforementioned polytype heterostructures and therefore additional opportunity for heterojunction formation. There are only two experimental works reporting about epitaxial growth of (Si_(1-x)C_(1-y))Ge_(x+y) alloys. The challenges in this ternary system are the immiscibility of Ge in the SiC lattice, the low de-sorption temperature of Ge compared to Si on the SiC surface and the tendency of Si- and Ge-cluster formation during SiC epitaxial growth. The ion implantation of Ge in SiC provides the possibility to overcome this obstacles attendant to the growth process. The ion beam synthesis allows the incorporation of Ge atoms above the thermodynamical Ge misci-bility limit and leads to the formation of (Si_(1-x)C_(1-y))Ge_(x+y) alloys. Up to now only a few investigations on Ge implantation in hexagonal SiC (4H-SiC and 6H-SiC) have been carried out at different implantation conditions and post implantation treatments. The following results have been obtained. The amorphisation dosis at room temperature Ge ion implantation in the SiC lattice was found to be about 3 x 10~(14) cm~(-2) Polytype transitions from hexagonal into the cubic polytype and phase separation of Ge nanocrystalls in the SiC host material occurred at annealing temperatures between 1400 and 1600℃. The formation of compressive strained 4H-SiC:Ge layers at an implantation temperature of 1000℃ was also observed.