Influence of the Grain Boundary Electric Field on the Absorption Edge in Semiconducting Polycrystals

Abstract

In disordered semiconductor materials an increasing of the tail parameter and a softening of the absorption edge is commonly observed. In semiconducting polycrystals the grain boundary influences considerably on the material characteristics. In this work we modeled the influence of an electric field due to ionized traps of the grain boundary under the consideration of a localized and spatially dependent Franz-Keldysh effect (FKE) in a spherical grain. The model reproduces and explains the contribution of this effect to the softening of the absorption edge in these materials. From the model the absorption edge extends toward energy below the band gap energy, which constitutes an important feature to take into account in the analysis of this region. Comparison of the model with experimental absorption measurements in polycrystalline CdTe films was also carried out with the aim of estimating the weight of the FKE in the energy band tails.