High electron mobility large grain polycrystalline epitaxial Germanium on Silicon using liquid phase crystallization for III-V photovoltaic applications

Abstract

Germanium is considered an important electronic material which can serve both as a photo-voltaic material as well as a substrate for low cost III-V solar cells on silicon. However, growth of high quality germanium on silicon is challenging due to 4% lattice mismatch. In this work, we present growth of epitaxial, large grain polycrystalline germanium on silicon using liquid phase crystallization. The method involves re-crystallization of PECVD deposited amorphous Ge on Si using a two-step annealing process by melting (937oC) amorphous thin film and cooling it right below the melting point leading to high quality and large grains. SEM XRD and hall measurements were done to evaluate the material and electronic quality of the films. The films cooled near melting point were found to have largest grains of size ~14 μm and XRD rocking curve FWHM of as low as ~300 arc-sec. Films also demonstrated record high electron mobility of 500-1000 cm2Vs-1.The process is scalable and orientation agnostic with comparable film quality for all orientations.