The purpose of the present work was to develop an accurate and fast method for modelling the capacitance-voltage profiles of high-Iow junctions and isotype heterojunctions. Various other models exist to simulate dopant profile in semi conductors. poisson's equation from the surface of the semiconductor towards Ail these models, however, proceed by integrating the interior using an Iterative scheme for the field potential until the solution for the conduction band edge (assuming an n-type semiconductor) satisfies the boundary conditions in the bulk of the semiconductor . This scheme is, however, time consuming and if the convergence is not good enough, there may be instability problems . We have, as a consequence, developed an entirely new approach to integrating poisson's equation starting from the interior (junction) towards the surface relying on the fact that for a homogeneouS semiconductor which is semi-infinite in extent, there is a simple analytical relationship between the slope of the conduction band or electric field and the potential at any point . Because no iteration is involved, the computer model developed is very fast and when implemented on the HP 9825 A desktop computer, takes from 1O minutes ( for a junction depth of. 2 ~ to about 50 minutes (for a junction depth of 1 \Jm) to output a simulated doping profile. Extensive computer simulation of high-Iow junctions and isotype heterojunctions were successfully undertaken in the previous chapters. The computer model presented is very flexible and modif ications such as carrier degeneracy and fixed interface state charges can easily be accommodated as demonstrated in Chapter V. A further consideration that should be mentioned is the quantization of the two dimensional electron gas in the accumulation layer of the narrow gap semiconductor. namely GaAs. Such effects may not necessarily be negligible in GaAs. because of its small electron effective mass. Because the computer program can easily be adapted to plot \ \ , f ! , t ( r ! l t f f f l r . I : The good agreement. however. between the theoretical and experi mental doping profiles shown in Chapter VI. implies that the effect of sub-band quantization is not important. at Jeast for the particular parameters involved . carrier concentrations. it is also very convenient for modelling modulation doped Field Effect Transistors . The Debye length smearing that occurs in semiconductors has precluded the extraction of the true doping profile from the raw C-V data in the general case and one must be content with t t l f k t f , ~ c approximate results which may be aided by insight gained from simulating various types of doping profiles.