Cathodoluminescence investigation of stacking faults extension in 4H-SiC
Résumé
We report the results of a cathodoluminescence (CL) investigation performed on as-grown stacking faults in a thick, undoped, 4H-SiC epitaxial layer grown by CVD. To investigate the size and optical signature of the defects we used, first, room-temperature (RTCL) and then low-temperature (LTCL) spectroscopy. From RTCL we find that all defects have identical optical properties, with a maximum emission wavelength centered at 480 nm at 300 K. We find also that the defects have a triangular shape, with large extension in the basal plane. This makes them intermediate between the usual (semi-infinite) quantum wells (QWs) and pure (zero-dimensional) quantum dots. From a comparison of the LTCL results with a simple computation, we determine the QW thickness and find that all SFs are made of 4 bilayers of 3C-SiC polytype embedded in the 4H-SiC matrix. Scanning across one single (isolated) triangular defect, we then find that the maximum signal wavelength shifts, depending on the excitation spot position over the defect. To the best of our knowledge, this is one of the few experimental evidences of a screening of the built-in electric field when increasing the carrier concentration in a fault. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.