Optical monitoring of nonequilibrium carrier diffusion in single crystalline CVD and HPHT diamonds under high optical excitation

We report on a novel approach for the contactless, all‐optical study of ambipolar carrier diffusion in single‐crystalline diamond layers. Using interband two‐photon and single photon absorption (at 351 nm and 213 nm), we created a spatially‐modulated free‐carrier light‐induced transient grating and monitored the in‐plane carrier diffusion in a wide range of injected carrier densities (10 15 cm –3 to 10 18 cm –3 ) and temperatures (80 K to 800 K). A drastic decrease of the ambipolar diffusion coefficient from ∼50 cm 2 /s at low injections to 6–10 cm 2 /s at high ones was observed at room temperature and even stronger at lower temperatures. The modelling based on bandgap renormalization and electron–hole scattering provided a fit to the injection‐dependent diffusivity. The determined low‐injection ambipolar mobility data for CVD layer were found in a good agreement with electrical time‐of‐flight measurements. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)