The scattering of 2 MeV He+ in amorphous germanium

The surface of single crystal germanium is amorphized to varying depths by the implantation of N+ ions ranging in energy from 200 keV to 400 keV. The ion dose used is 5 x 1015 ions cm-2. The yield of backscattered 2 MeV He+ ions due to the random fraction of the analysis beam is calculated using established iterative methods and compared with the observed yield when a major axis of the crystal is aligned with respect to the analysis beam. These comparisons show that good agreement is obtained by assuming that a single scattering mechanism is responsible for scattering ions out of the aligned beam, especially if the mean energy loss of the analysis beam as it traverses the amorphous region is taken into account, provided the dechanneling angle, psisub(c) is treated as a variable parameter. The range of the disorder is compared with the mean and total range of N+ ions as predicted by various authors. Investigation of a 200 keV N+ implant which had been progressively annealed to a temperature of 4500C shows that the iterative method of analysis used to extract information about disorder profile is questionable in cases where the disorder is not randomly distributed. (author)