REAL SPACE TRANSFER: GENERALIZED APPROACH TO TRANSPORT IN CONFINED GEOMETRIES

Research on transfer of electrons between semiconductor heterolayers is reviewed and its importance and applications in new forms of heterolayer-structures are discussed. It is shown that the massive transfer of hot electrons transversal to the layers is interesting from both a device and a physics point of view due to the high speed of the effect and due to its dependence on the details of the electron energy distribution under conditions far away from equilibrium. Less visible but of no lesser importance for the understanding of transport phenomena is the spreading of hot electrons in confining fields such as the gate field in field effect transistors. This spreading can be viewed as a real space transfer effect and causes additional mobility degradation and generally the enhancement of effects of nonlinear transport, notably impact ionization. The transfer of minute electron numbers from silicon into silicon dioxide appears as a special case of real space transfer from this point of view. It will be shown, however, that a complete understanding of this latter effect involves complex quantum-transport principles. Finally, details of nonlinear transport of electrons over a well structure will be discussed. It will be shown that interesting combinations of k-space and real space transfer effects can be achieved which have potentially n e w applications. These effects vividly demonstrate the influence of the band-structure (band-gap engineering) on the energy distribution function of the electrons.