Investigation of n-doping in CVD diamond using gap states spectroscopy

Abstract

In-situ doping of CVD diamond with N and Li using N-2 and a Li-containing organometaliic precursor was investigated. Photothermal deflection spectroscopy (PDS) was used to study optical transitions from localized electronic states in the bandgap of CVD diamond resulting from the presence of extrinsic and intrinsic impurities. The advantage of PDS is its sensitivity, which allows very low defect levels to be investigated even in thin diamond films. The optical absorption coefficient alpha of N-doped films (100 ppm N-2 in the gas phase) shows absorption bands characteristic of Ib diamond. When a Li-containing precursor is used, a deep defect state around 1.5 eV, which has not been reported previously, is observed. Optical transitions due to this defect state are superimposed on the characteristic background absorption present in all CVD diamond films.