In this paper we consider numerical methods for a singularly perturbed reaction-diffusion problem with a discontinuous source term. We show that such a problem arises naturally in the context of models of simple semiconductor devices. We construct a numerical method consisting of a standard finite difference operator and a non-standard piecewise-uniform mesh. The mesh is fitted to the boundary and interior layers that occur in the solution of the problem. We show by extensive computations that, for this problem, this method is parameteruniform in the maximum norm, in the sense that the numerical solutions converge in the maximum norm uniformly with respect to the singular perturbation parameter.
The semiconductor device equationsThe stationary behaviour of semiconductor devices can be described by the nonlinear system of second-order elliptic equations of van Roosbroeck [6]. In one dimension, for example, a simple p-n diode Ω = (0, 1) with two Ohmic contacts, an anode at x = 0 and a cathode at x = 1, is governed by the equationson Ω with appropriate boundary conditions at x = 0 and x = 1. Here ψ is the electrostatic potential, η and ρ are the electron and hole concentrations in the Slotboom variables, D denotes the doping function * Corresponding author.0168-9274/00/$ -see front matter © 2000 IMACS. Published by Elsevier Science B.V. All rights reserved PII: S 0168-9274(99 )00 1 40 -3