Effect of oxygen on the cathodoluminescence signal from excitons, impurities and structural defects in homoepitaxial (100) diamond films

Cathodoluminescence at 5 K is used to study the residual radiative defects in homoepitaxial diamond films deposited on the centre of the plasma ball versus the O/CH4 ratio from 0 to 0.375 in the feeding gas, and to understand their effect on the quality (intensity of the free exciton peaks) of the films. The addition of oxygen significantly reduces the slight boron contamination (1.6×1016 to 4×1014 cm−3) of these good quality (BENP exciton peak) non-intentionally doped films. As the O/C ratio increases, (i) the intensities of the boron-bound excitons, Nc-Vc, H3, Nc-Ic peaks, of the 2.3 eV wide band and the nitrogen contamination decrease (ii) the intensity of the N3 peak and the relative intensity of the A band increase. These opposite variations of the defects concentration as O/C increases result in a maximum of the FE peaks for O/C around 0.25.