Point defects induced in ion irradiated 4H-SiC probed by exciton lines

The defects produced in 4H-SiC epitaxial layers by irradiation with a 200 keV H+ ion beam in the fluence range 6.5 x 1011-1.8 x 1013 ions/cm2 are investigated by Low Temperature Photoluminescence (LTPL-40 K). The defects produced by ion beam irradiation induce the formation of some sharp lines called 'alphabet lines' in the photoluminescence spectra in the 425-443 nm range, due to the recombination of excitons at structural defects. From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P1 lines (e, f, g) and the P2 lines (a, b, c, d) that exhibit different trends with the ion fluence. The P1 group normalized yield increases with ion fluence, reaches a maximum at 2.5 x 1012 ions/cm2 and then decreases. The P2 group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 x 1012 ions/cm2 and decreases at higher fluence, reaching a value of 50% of the maximum yield. The behaviour of P1 and P2 lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.