Accurate determination of the free carrier capture kinetics of deep traps by space-charge methods

A detailed analysis of the pulsed bias techniques used to determine the capture kinetics of free carriers by deep traps in Schottky diodes or asymmetric bipolar junctions is presented. Both exact simulations, involving an exact integration of Poisson’s equation and a self-consistent treatment in the case of large deep trap concentrations and simple analytical approximations are given. The usual depletion approximation for the distribution of free carriers in the Debye tail is demonstrated to yield erroneous results in some occasions and it is shown how to deal simply with the exact distribution. A novel experimental technique is proposed to rigorously extract the exponential capture kinetics in the neutral semiconductor, from the total capture kinetics, getting rid of the capture in the Debye tail; it is also shown how it is possible to obtain a correct estimation of the capture rate from the capture in the Debye tail, when the direct determination by the above mentioned method is impossible.