High Quality Epitaxial Germanium on Si (110) using Liquid Phase Crystallization for Low—Cost III-V Solar-Cells

Germanium integration on silicon is required for fabricating high efficiency III-V low-cost solar cells on silicon. In this work, we present a single step thermal annealing of amorphous germanium films as a method of monolithic integration of epitaxial germanium on crystalline silicon (110) wafers. The re-crystallization progresses via liquid phase epitaxy by heating the germanium layer in inert ambient to right above its melting temperature of 937 ⁰C. On slow 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 crack free whereas XRD measurements indicated highly oriented films. 1 micron thick film had rocking curve FWHM of 0.15 degree corresponding to dislocation densities of low 10⁹ cm^-2. Also, AFM measurements indicate that 1 micron films have RMS roughness of ~ 80nm for scan area of 25 μm².