Selective porous silicon formation in buried p+ layers

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Abstract
We report a systematic microstructural study of enhanced lateral porous silicon formation in the buried p+ layers of n/p+/p− and p−/p+/p− structures. We find, surprisingly, extremely selective porous silicon formation due to the thin p+ layer in both structures, despite the absence of a p‐n junction in the p−/p+/p− structure. The interface between the isolated island and the buried porous silicon layer was always located at the depth where the net p‐type dopant concentration was 1–8×1015/cm3. The observed microstructure can largely be understood in terms of a recent model for porous Si formation in uniformly doped Si, proposed by Beale et al. [J. Cryst. Growth 7 3, 622 (1985)]. However, we also observe, for the first time, important effects unique to a nonuniform dopant concentration.