High Quality Epitaxial Germanium on Si (100) for low -cost III–V Solar-Cells
Integration of high quality germanium on silicon is prerequisite for fabricating high efficiency low-cost III-V solar cells on silicon. In this work, we present a method of monolithic integration of epitaxial germanium on crystalline silicon wafers where a single-step anneal in hydrogen ambient is used to recrystallize PECVD-deposited amorphous germanium into crystalline germanium. The re-crystallization progresses via liquid phase epitaxy by heating the germanium layer in inert ambient to just above its melting temperature of 937 °C. On cooling, the Ge layer gets oriented by the underlying Si (100) wafer, yielding an epitaxial Ge film on Si. SEM show that the films are continuous and void free. XRD pattern indicates highly oriented films. Symmetric Rocking curve measurements showed a thickness dependence with 1 µm thick film showing the lowest threading dislocation density (TDD) of the order of 108 cm−2. AFM measurements indicate surface measurements ~10 nm. Quality of epitaxy depends on thickness of film.