Carrier lifetime investigation in 4H-SiC grown by CVD and sublimation epitaxy

Depth-resolved carrier lifetime measurements were performed in low-doped ep itaxial layers of 4H silicon carbide samples. The technique used was a pump -and-probe technique where carriers are excited by an above-bandgap laser p ulse and probed by free carrier absorption. Results from chemical vapour de position samples show that lifetimes as high as 2 mus may be observed in th e mid-region of 40 mum thick epilayers. For epilayers grown by the sublimat ion method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the 'true' lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trap ping centres. From the saturation of this level at increased pumping we cou ld derive the trapping concentration and their depth distribution peaking a t the epilayer/substrate interface. (C) 2001 Elsevier Science Ltd. All righ ts reserved.