Cathodoluminescence imaging of defects and impurities in diamond films grown by chemical vapor deposition

Abstract

Defects and impurities in diamond films grown by chemical vapor deposition (CVD) were analyzed by high-resolution cathodoluminescence (CL) spectroscopy and imaging in transmission electron microscopy (TEM). The combination of CL and TEM makes it possible to correlate the film microstructure with the electronic structure due to defects. Broad CL bands observed at 428±1 nm (2.90±0.01 eV) and 551±1 nm (2.250±0.004 eV) are attributed to closely spaced and widely separated donor-acceptor (D-A) pairs, respectively. A narrow peak at 738.7±0.5 nm (1.679±0.001 eV) is attributed to interstitial silicon atom impurities. An additional wide band at 365±1 nm (3.40±0.01 eV) was not identified. The material was found to be type IIb (semiconducting) and varied in quality with the growth conditions. Impurities are evidently distributed nonuniformly on a submicrometer scale, and both highly faulted and defect-free grains were found to emit no visible CL. For the first time in CVD-grown diamond, band-A CL due to closely spaced D-A pairs was found to be directly correlated with dislocations. Widely spaced D-A pairs were more uniformly distributed throughout the film. The distribution of interstitial silicon impurities varied greatly from grain to grain, but was not correlated with any microstructure.