Study of the Junction Depth Effect on Ballistic Current Using the Subband Decomposition Method M. Ali. Pourghaderi* ¶ , Wim Magnus ○ , Bart Sorée*, Marc Meuris*, Marc Heyns* ¶ and Kristin De Meyer* ¶ * IMEC. Kapeldreef 75, B-3001, Leuven, Belgium {pourgham|magnus|soree|meuris|heyns|demeyer}@imec.be ○ Universiteit Antwerpen, Physics Dept. Groenenborgerlaan 171, B-2020 Antwerpen, Belgium ¶ Katholieke Universiteit Leuven, INSYS Kasteelpark Arenberg 10, B-3001 Leuven, Belgium Abstract A robust algorithm to get the chemical potential of the particle reservoirs for the self consistent full 2D Schrödinger-Poisson solver is proposed. Using this algorithm we study the effect of junction depth on ballistic current. Simulation results show that shallow junctions come with much better on to off current ratio while it keeps the on- state transconductance at the same level as the deeper junction device. 1 Introduction An efficient 2D Schrödinger-Poisson solver for modern MOS transistors becomes inevitable. When open boundary conditions are imposed, only a limited number of methods can be used. Among these methods, the subband decomposition method [1] or quantum transmitting boundary method [2] come with great advantages. In this method, the reservoir picture is used to calculate carrier injection from source and drain. In order to model also the accumulation in the lightly doped drain (LDD) regions for a transistor in the on-state, the transistor area covered by the simulation should at least partially include the source and drain regions. In this light the chemical potential in source and drain should be properly calculated. This calculation is crucial to correctly impose the Dirichlet boundary condition of the Poisson equation and to calculate ballistic current and carrier distribution. 2 Algorithm In each iteration, the chemical potential of a reservoir is calculated by assuming a 1D potential profile at the edge of the active area which can only be justified when we extend the active area far enough from the gated region. Fig. 1 shows such a wide active area and the coordinate axes used in the equations. For the region with a 1D potential profile the integral of the charge density in the confinement direction should SIMULATION OF SEMICONDUCTOR PROCESSES AND DEVICES Vol. 12 Edited by T. Grasser and S. Selberherr - September 2007 205