Observations of deep levels in 4H-SiC using optoelectronic modulation spectroscopy

Optoelectronic modulation spectroscopy (OEMS) has been used to reveal defect states in 4H-SiC. Pairs of magnitude and phase spectra have been used to infer whether they were electron or hole traps. Eleven discrete trap responses have been observed, eight were assigned as electron traps and three as hole traps. Five of these had been observed previously using optical admittance spectroscopy (OAS). An electron trap at 1.20 eV gave the most prominent response with a distinctive signature indicating that these traps were spatially delocalized with an extent of at least 1.35 nm, possibly associated with an extended defect structure. An unresolved continuum of hole traps was seen between 2.3 eV and 2.9 eV. A response at 0.72 eV appeared to be the superimposed response of an electron and hole trap at closely similar energies. Consistency has been demonstrated with previous work using DLOS and OAS.