Origin of band-A emission in diamond thin films - art. no. 245328

By means of scanning cathodoluminescence (CL) measurements, high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectro scopy (EELS), we have studied the origin of the band-A emission in homoepit axial diamond thin films grown using microwave-plasma chemical vapor deposi tion (CVD). A broad luminescence peak at around 2.9 eV, the band-A emission , was observed in homoepitaxial diamond films with nonepitaxial crystallite s (NC's), but not in the high-quality films without NC's. The scanning CL m easurements showed that the band-A emission appeared only at NC sites. TEM revealed that the NC's contained defects such as dislocations and several t ypes of grain boundary (GB). Further, HRTEM indicated that several types of incoherent GB existed within the NC's including five-, six-, and seven-mem ber carbon atom rings. These were the same GB's as those in polycrystalline CVD diamond films that had sp(2)-like structure of carbon atoms as indicat ed by the observation of the 1s-pi* signal in EELS. It is then reasonable t o consider that, if sp(2)-like structures behave as defects in the network of sp(3) structure of diamond, one possible origin of band-A emission might be the sp(2) defects in the GB's and dislocations. The band-A emission beh avior in homoepitaxial CVD diamond films is the same as that in polycrystal line diamond films. The origin of the band-A emission generally observed in many kinds of CVD diamond is discussed relative to these results.