Microstructural evolution of group IV based alloys on silicon

Heteroepitaxial growth of Group IV based alloys on silicon (Si) substrates is being pursued with renewed interest for possible applications ranging from the fabrication of nano-structures for quantum dot devices to growing strained layers for bandgap engineering and to growing completely relaxed buffer layers that are essential for device integration. Epitaxial growth of germanium (Ge) and silicon-carbon alloys (Si_1−yC_y) on Si substrates was carried out using standard molecular beam epitaxy (MBE) growth. Post-growth experiments were conducted primarily using high-resolution transmission electron microscopy (TEM). Electron-energy-loss spectroscopy (EELS), Rutherford backscattering spectroscopy (RBS) and atomic force microscopy (AFM) were also employed to elucidate information about the grown material. This investigation was directed towards understanding basic mechanisms in strain-related heteroepitaxy and fabricating high-quality heterostructures for next-generation technology.; All attempts to grow Si_1−yC_y alloys on Si (100)- and (811)-oriented substrates with moderate concentrations of carbon (1.5–3.0%) led to the formation of C-rich striations roughly parallel to the (100) plane. These striations exhibited rapid contrast fluctuations due to embedded C clusters in the Si matrix. The total C concentration was found to be weakly dependent on substrate orientation. This investigation confirmed that maximum substitutional carbon was obtained by depositing below 600°C.; The epitaxial growth of Ge on Si(211) substrates was carried out using surfactant-mediated growth. The use of arsenic (As) as a surfactant during MBE growth resulted in Ge epilayers with smoother surface morphology compared with samples grown without the use of As surfactant. Small probe microanalysis confirmed that As “floated” at the growth front during sequential deposition of Ge.; EELS was used to study Si-Ge intermixing in Ge/Si(100) self-assembled islands. Ge/Si alloying as a function of deposition temperature in the 400–700°C range has been quantified. Si content in the island varied from about 7% at 400°C up to 58% at 700°C.; The growth of Ge/Si(211) and Ge/Si(111) islands revealed a complex morphological evolution in that the substrate surface structure played an important role in the shape evolution. Growth on Si(211) led to irregular hexagonal-shaped islands. In contrast, growth on Si(111) led to rounded and triangular-shaped islands. Spatial ordering was observed.