Abstract:
A new numerical model for capacitance-voltage analysis of metal-semiconductor
contacts has been developed and used to simulate on various experimental results. The
model is based on self-consistency between Poisson's equation and Schrodinger's
equation for the numerical simulation of lD MIS structure. Poisson's equation has
been solved in the combined oxide-semiconductor region using Finite Difference
method with non-uniform mesh size and boundary value technique. Doolittle's
decomposition technique has been used to the tri-diagonal coefficient matrix to speed
up the Poisson solver. Eigen states, as well as the eigen energies are calculated from
the solution of ID Schrodinger's equation. To make the Schriidinger solver
numerically efficient and easy to program, Green's function formalism has been used
which uses retarded Green's function to find eigen energy and eigen states of any ID
quantum well structures using open. boundary condition. Interface trap charge
distribution in accordance with the Fermi - Dirac statistics has been included in the CV
curve considering both donor and acceptor type of trap states.
It has been observed that simulated C-V is sensitive to the variation of unintentionally
formed interfacial layer thickness. Numerical results show that C-V curves are rather
sensitive to the degree and details of the interface trap distributions. Non-unifrom
doping is also responsible for the non-ideal effects in the C2 vs Vg curves apart from
interfacial trap states distribution. A simple technique to extract doping profile from
experimental C-V curves has been developed. Results showed excellent agreement
with experimentally determined doping profile. Several C-V curves are simulated for
different types of doping profiles and doping profiles are extracted from them
subsequently to illustrate the robustness of the technique. An easy technique to extract
interface trap state distribution within the bandgap from low or high frequency C-V
curves has also been developed.