CATHODOLUMINESCENCE PROPERTIES OF DIAMOND FILMS SYNTHESIZED BY MICROWAVE-PLASMA-ASSISTED CHEMICAL VAPOR-DEPOSITION

A variety of diamond films were synthesized in microwave plasmas of the CO-N2-H-2, CO-B(OC2H5)3-H-2, CO-H-2-Ar and CO-H-2 systems. The correlation between their crystallinities and cathodoluminescence (CL) properties led to the following conclusions. Non-doped films had twin peaks at 2.82 eV (440 nm) and near 2.3 eV (530-600 nm) which were categorized as band A luminescence. The intensity ratio I2.8/I2.3 of these twin peaks was smaller than 1. This value became larger than 1 as a result of nitrogen doping. According to scanning electron microscopy observations and X-ray diffraction analyses, nitrogen was considered to be selectively incorporated into (111) sectors. Considerations of these experimental facts in conjunction with earlier findings led to the conclusion that (100) sectors emitted high energy (blue) band A luminescence (I2.8/I2.3 > 1) and (111) sectors were responsible for low energy (green) fluorescence (I2.8/I2.3 < 1). An intense green emission was observed for a boron-doped film, which had a peak at 2.34 eV (530 nm). This emission was classified as a lower energy peak (2.2 eV) of band A luminescence. Boron-doped films exhibited green emission (2.34 eV, 530 nm) of band A luminescence five times as intense as that of non-doped films, whereas nitrogen-doped films exhibited only a little increase in the intensity of the blue emission (2.8 eV, 440 nm) of band A luminescence. The intensity of the blue emission was presumed to increase by enhanced nitrogen incorporation into (100) sectors. A sharp peak corresponding to the GR1 band was observed at 1.67 eV (741 nm) for the film synthesized in a CO-H-2-Ar system. This luminescence originated from the vacancies in the diamond film synthesized under severe bombardment of high energy electrons and ions in the argon-involving plasma. Argon addition to a CO-H-2 system suppressed the CL intensity of the synthesized diamond film which was characterized by a relatively intense red emission (GR1) at 1.67 eV (741 nm).