Smooth, 3D Ge transistor channels by heteroepitaxial growth

Crystalline germanium (Ge) is a prime candidate as a material for high-performance transistors due to its higher electron and hole mobility with respect to those of silicon. In this study, we present a novel method of fabricating epitaxial Ge structures of high crystalline and morphological quality directly onto Si substrates, in which 3D Ge structures are grown by selective epitaxy then annealed in a hydrogen ambient at 850 °C. Under such annealing, the surface of the Ge structures deform by surface diffusion to form smooth, rounded shapes for which the surface energy is at a local minima. The apparent smoothness of the surface, along with the decreased defect density expected to exist in these heteroepitaxial Ge structures, suggest they are adequate for use as transistor channels.