The ambipolar diffusion coefficient in silicon: Dependence on excess-carrier concentration and temperature

Abstract

Recent articles have been published claiming that the ambipolar diffusion coefficient of semiconductors,D a , is basically independent of the excess‐carrier concentration, thus contradicting the conventional result of, for example, Fletcher. However, only a few experimentally verified papers on this subject are published. In the present work, a detailed experimental analysis of the ambipolar diffusion coefficient is presented regarding both temperature and injection‐level dependence. The ambipolar diffusion coefficient was measured in the low‐doped n base of a p‐i‐n type diode at different excess‐carrier concentrations and temperatures using an open‐circuit carrier decay (OCCD) method based on the free‐carrier absorption (FCA) technique. This investigation was performed in the carrier‐concentration range of 1015–2×1017 cm−3 and in the temperature range of 300–420 K, respectively. The ambipolar diffusion coefficient is experimentally found to behave in reasonable agreement with Fletcher’s theory, thus decreasing with increasing excess‐carrier concentration.