Unpredicted Internal Geometric Reconfiguration of an Enclosed Space Formed by Heteroepitaxy

Epitaxial lateral overgrowth (ELO) over a free-standing dielectric mask is an unexplored territory in selective epitaxy growth (SEG) of semiconductors. By shrinking the dielectric mask dimension to the micron scale, the growth fronts from ELO are able to converge and coalesce, thus providing the freedom to engineer the interfacial structure between the epi-layer and dielectric mask. We demonstrate, herein, anomalous adatom diffusion and migration at the Ge/SiO₂ interface upon SEG on a Si (100) wafer. We find, depending on the oxide strip length, a polyhedral cavity or tunnel can form on the oxide layer. More importantly, we observe a thermally induced substantial internal surface reconfiguration process of Ge atoms that connects two tunnels and one cavity in order to form a single tunnel. Defect-free Ge above the oxide strips is obtained after coalescence. Our findings yield new insight into adatom migration in an enclosed space, and the cavity and tunnel show the first known three-dimensional geometric configuration in selective heteroepitaxial structures.