Low temperature diffusion length of excitons in gallium nitride measured by cathodoluminescence technique

Monochromatic cathodoluminescence (CL) images of threading dislocations in GaN epitaxial layers were observed using a transmission electron microscopy combined with CL system. The carrier diffusion lengths were derived from the free exciton emission intensity profile of the dislocation contrast in the CL images. The carrier diffusion lengths in Si-doped and Mg-doped GaN were nearly the same and shorter than that in undoped GaN in the temperature range from 20 to 140 K, respectively. Moreover, the temperature dependence of the diffusion length shows that the acoustic phonon scattering mainly affects the exciton diffusion process at low temperatures from 40 to 120 K.