Mobility gaps: a mechanism for band gaps in melanins.

The semiconductor behavior of melanins is reviewed and compared with quantum mechanical models of conduction in amorphous solids. The available data are consistent with extensions of Mott's basic model for amorphous semiconductors, whereas they are inconsistent with crystalline semiconductor models. An investigation of the specific conduction mechanisms operative in melanins in terms of the amorphous model should reveal important aspects of the band structure.