In p-n heterojunctions of type 1, the situation is possible when space charge density in them (and consequently built-in voltage of the junction) is formed by not only by ionized impurities but also by free current carriers. Under such conditions, usual depletion approximation turns out invalid and Poisson’s equation becomes nonlinear. In this paper, Poisson’s equation with dominant free minority carriers is solved analytically, and it is shown that taking their contribution to space charge into account increases both the built-in potential and width of the space charge region of the heterojunction.
V. L. Borblik (Wed,) studied this question.