Controlled Drying: The Key to Better Quality Porous Semiconductors

Abstract

The importance of drying nanostructured semiconductors, such as porous silicon, in a controlled manner is explained. The mechanical instabilities that can arise during drying—resulting in cracking (see Figure) or peeling of the film—are discussed, as are methods that reduce or completely suppress these drying stresses, for example, supercritical drying, freeze drying, and “drying with pentane”.

Determining Protein Size Using an Electrochemically Machined Pore Gradient in Silicon

“…The porous Si formation conditions in this region result in high porosity Si that is susceptible to cracking and peeling upon drying. [20] Uniform, reflective porous Si is observed adjacent to this region (Fig. 2A3) and extends to the far edge of the film.…”

Silicon Porosification: State of the Art

“…When the pore size is in the range of a few nanometers, capillary stresses, g LV , can be as large as a few tens of megapascals (with g LV = 72 mJ/m 2 as for water). 507 Therefore, it is usually impossible to obtain a porosity of layers higher than 90% to 97%. 508 Figure 91a displays the cracking pattern, as revealed by scanning electron microscopy (SEM), of PSi layer after the evaporation of water inside the pore network.…”

Thermal Properties of Porous Silicon

“…Bellet and Canham (1998) and many other authors (Mason et al 2002;Bouchaour et al 2004) believe that local variation in porosity causes the increase of asymmetric capillary forces, which induce fracturing of the PSi network. Due to capillary tensions that occur on the branch surfaces during drying, the complete disintegration of the branches could happen.…”

“…Due to capillary tensions that occur on the branch surfaces during drying, the complete disintegration of the branches could happen. When the pore size is in the range of a few nanometers, capillary stresses, g LV , can be as large as a few tens of megapascals (with g LV = 72 mJ/m 2 as for water) (Bellet and Canham 1998). Therefore, it is usually impossible to obtain a porosity of layers higher than 90-95% .…”