Formation of Three-Dimensional Semiconductor Metalattices Via High-Pressure Chemical Vapor Deposition in Nano-Templates

Three-dimensional semiconductor metalattices can be fabricated by high pressure chemical vapor deposition within nano-templates such as those provided by nano-opals. In the deposition process, a high-pressure (~30 MPa) germane/helium mixture flows through the nano-opal template at elevated temperature. Germane decomposes at the surface of silica spheres to deposit a germanium film. Because the pore structure within the template is characterized by passages whose cross-sectional areas vary substantially in the longitudinal direction, the throats or mesopores in the entry region of the template can get blocked when the time scale for reaction is small compared to that for transport of the precursor.  This can lead to limited deposition in the larger pores by cutting off the precursor supply when diffusion is the dominant mechanism for precursor transport within the pores, thereby ruling out complete filling of the nano-template.  We model the opal structure as an ideal face-centered-cubic packing of silica spheres, and perform numerical simulations of germane transport and decomposition within the model structure.  Our results show that complete infiltration of nano-opals can be achieved at high pressures by establishing flow of the precursor within the opal to supply precursor to the larger pores by convection.