A novel technique for the simultaneous measurement of ambipolar carrier lifetime and diffusion coefficient in silicon

Abstract

Using the classical semiconductor continuity equation, a new method for the simultaneous extraction of the ambipolar carrier lifetime and the ambipolar diffusion coefficient for high injection levels is developed. The method uses carrier decay measurements based on the free-carrier absorption (FCA) technique. The measurements are performed in the base of p- i- n type diodes, where the middle region is a lightly n-doped base region. By varying the forward bias, the ambipolar lifetime and diffusion coefficients are studied for different excess-carrier concentrations ranging approx. 2–4 decades above the base doping. Both the lifetime and diffusion coefficients agree well with theoretical models. The theoretical ambipolar diffusion coefficients agree well with theoretical models. The theoretical ambipolar diffusion coefficient is calculated using the values of D n and D p , which, in turn, are determined from mobility models and the Einstein relation. The mobility models used include carrier-carrier scattering effects which are important in the explanation of high-injection dependence.