Talk abstract

The aim of this talk is to introduce a new technique with considerable promise for studying point defects at the ppm level and below in wide band-gap semiconductors and devices. There are many advantages of using a TEM for electron irradiation. These include efficiency, flexibility and control. Efficiency because many irradiations can be carried out on a specimen (bulk mainly at present but it could also be electron transparent) during one three-hour electron microscope session. Flexibility because of the ability to vary dose, dose rate, specimen temperature, crystallographic orientation and area. Control because the electron accelerating voltage can be set and measured to any desired accuracy so that damage may be introduced very close to the displacement threshold for any chosen sub-species in the lattice. Subsequent examination of the specimens is carried out at liquid helium temperatures using an Oxford Instruments continuous flow cryostat attached to the microscope stage of Renishaw micro-Raman spectrometers (experiments have been carried out using 244, 325, 457.9, 488, 514.5 and 633 nm laser as excitation sources). By control of the electron energy the displacement thresholds for Si and C displacements in 6H and 4H SiC have been determined. By comparing the spectra obtained from within the irradiated regions to those obtained outside, species that migrate under the conditions of irradiation can be identified. By use of isotopes the involvement of a particular dopant in the optical centre can be identified and the dumbbell form of certain interstitial related centres can be deduced.