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

Abstract

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 (1015 cm(-3) to 1018 cm(-3)) and temperatures (80 K to 800 K). A drastic decrease of the ambipolar diffusion coefficient from similar to 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. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim