RBS ion channeling study of low concentrations of ion implanted samarium in GaN

Abstract The purpose of this work is to determine the location and depth profile of samarium implanted into gallium nitride. The concentrations of the dopant are extremely low (∼100 ppm) which means that the measurements take a large integrated charge to complete so that a pulse pile up system must be employed to enable count rates up to 100 kHz to be used. Although the dopants are more massive than the substrate they are still difficult to resolve with 2 MeV RBS. By taking advantage of the α-particle energy available from a 4.5 MV tandem, spectra have been obtained where the rare earth dopants are easily visible. Using ion channeling angular scans across more than one axis it is possible to confirm the extent to which an impurity is substitutional, interstitial or randomly located in the host lattice. For the GaN wurtzite lattice with the c -axis 〈1 0 0 0〉 perpendicular to the surface the alternative axes are 〈11 0 1〉 and the 〈1 1 2 1〉. The data show that samarium is substitutional to a level of about 80% with the remainder randomly located in the lattice. Although there is a higher concentration of the rare earth closer to the surface, the substitutional fraction does not change significantly as a function of depth. The samarium concentration in the sample varied from about 100 ppm at ∼300 nm below the surface to about 300 ppm at the surface.