Photoluminescence and diffusivity of free excitons in doped silicon

The diffusivity of free excitons (FE) in an inhomogeneously doped Si sample is evaluated by spatially resolved photoluminescence. The FE lifetimes and diffusion lengths are directly measured between 12 and 23 K. The FE diffusivity is found to be ~11 cm²/s at 12 K and increases with temperature. Exciton diffusion in doped silicon is found to be governed by their capture and release from neutral impurities. Implications of these measurements for the use of low-temperature photoluminescence as a method of spatially profiling dopant distributions are discussed.