TEMPERATURE-DEPENDENCE OF CATHODOLUMINESCENCE FROM CVD DIAMOND

The cathodoluminescence spectra from many polycrystalline films of diamond produced by chemical vapour deposition show a characteristic group of emission lines at 2.33, 2.42, 2.48 and 2.57 eV superimposed on the long wavelength tail of the blue band A, together with another line at 2.99 eV near the peak of band A. The intensities of these lines decrease as the temperature is increased from 120 to 200 K, and the band A intensity increases in this temperature interval. At slightly higher temperatures the band A intensity begins to decrease, and is very much weaker at room temperature. We present a simple model based on thermal detrapping of the excitons which accounts reasonably well for the temperature dependences observed. The thermal ionisation energy derived for band A is the same as that obtained in previous measurements of this band in natural diamond.