Investigation of surface recombination and carrier lifetime in 4H/6H-SiC

A spatially and time-resolved free carrier absorption method is applied to quantify surface recombination losses as compared to the bulk in 4H- and 6H-SiC structures. The observed carrier lifetime variation is discussed in terms of crystalline quality, top-surface properties and junction effects at the epilayer-substrate interface. Surface recombination parameters in epilayers with differently processed surfaces are extracted from fitting experimental data with numerical simulations. The as-grown bare epilayer is characterized by 104 cm s−1 surface recombination velocity. Mechanical polishing increases this parameter to 5×105 cm s−1. No noticeable passivation of 6H-SiC surface by an oxide film is observed, whereas an increase of the surface recombination velocity up to 105 cm s−1 has been detected after dry oxidation of 4H-SiC.