Simulation of current transport in highly doped semiconductor structures including the tunneling effect

Novel semiconductor struclures with shrinking dimensions and increasing doping result in veiy steep interfaces. The implementation of quantum mechanical effects into the compact model characterizing the current flow is a necessity and considerably contributes to the siniulation of various non-standard effects. Thus the analysis of the dependence of the properties of a tunnel diode on the actual doping profile of the structure is straightfonard. In a tunneling diode with an abrupt doping profile, tunneling through the p+-n' junction is likely to be the dominant mechanism which controls the current flow through the interface. Simulation based on the drift-diffusion approximation is unable to give the corresponding electrical characteristics and results [ 1-71. Various complex analytical models describing the tunneling effect have been developed [8-91 but usually they do not take into account the whole complexity of mutual interactions of different mechanisms of the current flow through the interface. Therefore in our approach the tunneling effect is introduced into the simulator via modification of a general generation-recombination term. The resulting compact formula characterizing the total current flow includes the drift and diffusion, Shockley-Hall-Read generation and recombination, Auger recombination, impact ionization and tunneling as well as the mutual interactions of the mentioned mechanisms of current flow. The properties of the modified simulator were verified by its application to the simulation of the I-V properties of tunnel diodes with different doping profiles and the contribution of the tunneling current to the total current is clearly demonstrated. 2. Theory Adding the tunneling mechanism via an additional generation - recombination term into the current continuity equations modifies the classical drift-diffusion model of the simulation of electrical properties of semiconductor devices. We can then write