New contactless method for carrier diffusion measurements in silicon with a high precision

Abstract

A novel, contactless transient grating method is demonstrated for excess carrier diffusion coefficient determination at an arbitrarily chosen injection density. The method is based on free-carrier absorption decay measurements along a grid of carriers excited in the bulk of the sample by a YAG laser pulse. The focused infrared probe beam, with an excess-carrier detection limit as low as 1012 cm−3, monitors the lateral interdiffusion of carriers by scanning across the carrier grating. Measurements on a 1015 cm−3, p-doped Si sample at injection levels in the range 1013–1017 cm−3 show a considerable reduction of the carrier diffusion coefficient at injection levels Δn ≥ 1016 cm−3.