SPACE-CHARGE EFFECTS ON DOPANT DIFFUSION-COEFFICIENT MEASUREMENTS IN SEMICONDUCTORS

Systematic errors are likely to affect the results of indirect methods used for measuring dopant diffusion in semiconductors, which, for thi s purpose should be considered as mixed electronic-ionic conductors. T he highest contribution to these errors is introduced by the presence of an internal electric field, i.e., by space charge effects. The elec tric field can be the result either of a dopant concentration gradient or of external bias, applied during the measurement. We consider here three methods in detail, viz. measurement of p-n junction motion, of current or potential decay, and of the time dependence of capacitance (transient ion drift). We show that space charge effects can lead to o verestimating diffusion coefficients by a few orders of magnitude. We use the results of our analyses to review and compare the experimental data obtained by different direct and indirect methods, for Cu diffus ion in CuInSe2, an issue of considerable current interest for solar ce lls. (C) 1998 American Institute of Physics.