TRANSIENT RESPONSE OF GRADED-BASE TRANSISTORS

Basic transient properties of graded-base transistor have been examined in terms of the minority-carrier distribution in the base region, subject to the restricting conditions of a one-dimensional device geometry and low injection. The mathematical expressions for the minority-carrier distributions in the base region and for the transient times have been found. The method used was to apply various boundary conditions to the one-dimensional diffusion equation which was solved by the 'separation of variables' technique. In order to satisfy the initial conditions of individual solutions, the general solutions of the transient times are formulated in terms of infinite series. Approximate, closed form solutions for the transient times are obtained by neglecting the higher order terms of the series. The closed-form expressions for the transient times offer good approximations for small values of f and reduce to the expressions obtained for homogeneous-base transistors when f is allowed to go to zero. (Author)