| Germanium (Ge) has been an attractive candidate to augment Si-based complementary metal oxide semiconductor (CMOS) devices and monolithic integration of optoelectronic devices as well. It is a key factor to grow high quality Ge heteroepitaxial films on a Si substrate for applicable high performance device applications. However, up to now, heteroepitaxy of Ge on Si is not straightforward because there is about 4.2% lattice mismatch between Ge and Si materials. A number of misfit dislocations (MDs) and subsequently threading dislocations (TDs) are easily formed in the epitaxial layers to relieve the mismatch strain. Three dimensional island growth of Ge on Si, which is called a Stranski-Krastanov (SK) mode, results in very rough surface morphology. The inclusion of the dislocations and roughness hinders not only high speed carrier transport but also modern state-of-the-art fabrication process.; In this thesis, for high mobility device applications such as MOS field effect transistors (MOSFETs) and modulation doped field effect transistors (MODFETs), a finite size pattern guided epitaxial growth method, which is called nanoheteroepitaxy (NHE), has been investigated to obtain high quality SiGe or Ge heteroepitaxial films. The NHE involves the fabrication of a nano scale SiO2 patterned template and the growth of heteroepitaxial films using a solid source molecular beam epitaxy (SSMBE) system. Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), etch pit dislocation (EPD) measurements, and Hall mobility measurements were employed to characterize the epitaxial films.; As a result, the heteroepitaxial films grown on the nano patterned templates exhibit comparably superior material quality compared to the films prepared by a conventional 2-D non-patterned growth. We also obtained the size dependent properties of etch pit dislocations, surface roughness, and carrier mobilities using different sizes of patterned templates. The results indicate that interface roughness and dislocation scattering factors, which are dominated in the heteroepitaxial films, can be effectively reduced by this approach. It thus suggests that the NHE technique may be a promising and plausible method to achieve high mobility device performances for those kinds of lattice mismatched heteroepitaxial growth systems. |
