Carrier recombination and diffusivity in microcrystalline CVD‐grown and single‐crystalline HPHT diamonds

Abstract

AbstractWe report investigation of carrier recombination and diffusivity in bulk diamonds of different crystalline structure – microcrystalline (MC) CVD‐grown and single crystalline HPHT diamonds. Presence of neutral and positively charged nitrogen and hydrogen defects was determined from NIR and UV–IR absorption spectra. Carrier injection into 1‐mm thick bulk layers was realized by two‐photon absorption at 351 nm wavelength. Carrier lifetimes of 150–330 ns in IIa type HPHT crystals correlated with N density, while the lifetimes in CVD crystal exhibited very fast (80 ps), slower one (3–8 ns), and µs‐duration thermally‐activated (∼1.5 eV) decay components. The initial two components correlated with the grain size at the front and backsides of the MC diamond. Linearly increasing with injection carrier recombination rates were observed in both CVD and HPHT samples at 800 K, and fitted with effective recombination coefficient B = 3–4 × 10−9 cm3/s. Ambipolar mobility and thermal diffusivity parameters in CVD and HPHT bulk crystals were measured by light‐induced free carrier and thermal grating techniques.