Elemental Analysis on Group-III Nitrides Using Heavy Ion ERD

Abstract

Elastic recoil detection (ERD) using energetic heavy ion beams (e.g. 170 MeV ¹²⁷I) is a suitable method to measure depth profiles of light and medium heavy elements in thin films. The main advantages of ERD, which makes it favorable over many other techniques for elemental analysis, is the possibility to obtain reliable and quantitative results, a sensitivity in the ppm region or a depth resolution even better than 1 nm.

ERD analysis was employed to obtain quantitative information about the aluminium content x in MBE grown Al_xGa_1−xN layers on Al₂O₃ substrates. Using this stoichiometry information and the lattice constants obtained from high resolution X-ray diffraction, Vegard’s law could be confirmed with high accuracy. Secondly, nitridation of heated Al₂O₃ substrates in NH₃ atmosphere was investigated using high resolution ERD. A substantial nitrogen content on the surface of the substrate was detected which means a nearly complete AIN layer grown on the Al₂O₃ surface by a heat treatment only. Such a nitridation layer can be the base for further growth of nitrides on Al₂O₃ surfaces. As a third, the impurity content of group III nitrides was investigated in dependence on deposition conditions for both, MBE and MOCVD grown samples. In all samples investigated an oxygen concentration larger than 100 ppm was detected which is much higher than the intrinsic charge carrier density of these samples. In addition it is shown that the efficiency of p-doping by Mg may not only be hindered by hydrogen but also by carbon impurities.