Pronounced Effect of pn-Junction Dimensionality on Tunnel Switch Threshold Shape

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Designing tunneling junctions with abrupt on-off characteristics and high current densities is critical for many different devices including backward diodes and tunneling field effect transistors (TFETs). It is possible to get a sharp, high conductance on/off transition by exploiting the sharp step in the density of states at band edges. The nature of the density of states, is strongly dependent on quantum dimensionality. To know the current/voltage curve requires us to specify both the n-side dimensionality and the p-side dimensionality of pn junctions. We find that a typical bulk 3d-3d tunneling pn junction has only a quadratic turn-on function, while a pn junction consisting of two overlapping quantum wells (2d-2d) would have the preferred step function response. We consider nine physically distinguishable possibilities: 3d-3d, 2d-2dedge, 1d-1dend, 2d-3d, 1d-2d, 0d-1d, 2d-2dface, 1d-1dedge and 0d-0d. Thus we introduce the obligation to specify the dimensionality on either side of pn junctions. Quantum confinement, or reduced dimensionality on each side of a pn junction has the added benefit of significantly increasing the tunnel conductance at the turn-on threshold. Introduction When designing tunneling junctions it is desired to achieve a very sharp turn on at low voltages. This is critical for backward diodes (1-4) and Tunneling Field Effect Transistors (TFETs) (5, 6). By using a sharp tunneling based switch it will be possible to significantly lower the voltage compared to conventional electronics. To attain a sharp turn, the band edge energy filtering mechanism, or density of states overlap turn on, appears most promising. This mechanism is likely to provide high conductance, as well as sharp switching(7). This is illustrated in Fig. 1. If the conduction and valence band do not overlap, no current can flow. Once they do overlap, there is a path from filled valence band states to empty conduction band states for current to flow. Above threshold the turn on characteristic will be determined by the overlapping density of states in the conduction band and valence band. For example, we will find that in a …