Sub-gap optical properties of ion implanted SiC

[0001] 6H-SiC was implanted with Bi ions at room temperature. The relative defect concentration nd,, was determined by Rutherford backscattering spectrometry, and the optical properties in the photon energy range 0.7 eV less than or equal to fi omega less than or equal to 3.2 eV were analysed using transmission and reflection measurements. For n(dat) less than or similar to 0.15 the layers contain mainly point defects and point defect complexes and the occurrence of a refractive index change can be largely excluded. The measured transmission can be simulated assuming an exponential sub-gap absorption tail which is superimposed on a broad absorption band in the range 1.3 eV less than or equal to fi omega less than or equal to 2.4 eV. Amorphous SiC is characterized by a refractive index change of 30% with respect to the unimplanted substrate and by an optical gap of 1.3 eV. In the case of medium damage (0.15 < n(dat) < 1), analysis of the transmission spectra indicates the existence of amorphous zones and of point defects and point defect complexes in the crystalline regions between the amorphous zones in the implanted SiC layers.