A brief Summary Of unusual vertical electrical behaviour obtained in GaAs/InAs/GaAs quantum Well and quantum dot Structures, Si/Ge/Si and Si/SiGe/Si structures containing nanometer size amorphous thin layers or quantum wells, SiC/Si and Fe2Si/Si Structures containing nanocrystals, and porous Si/crystalliec Si Structures, is presented, The unusual behaviour are connected either with defects (interface, bulk or band tail energy states), or quantum mechanical effects. (c) 2005 Elsevier B.V. All rights reserved.