Elemental Analysis on Group-III Nitrides Using Heavy Ion ERD
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ABSTRACT Elastic recoil detection (ERD) using energetic heavy ion beams (e.g. 170 MeV 1271) 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 AlxGalixN layers on A120 3 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 A120 3 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 A120 3 surface by a heat treatment only. Such a nitridation layer can be the base for further growth of nitrides on A120 3 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.
INTRODUCTION The electrical and optical behaviour of group III nitrides is related to the structure and composition of this wide bandgap material. Elastic recoil detection (ERD) analysis utilizing energetic heavy ions is applied in order to obtain quantitative information on the elemental content. This information can be correlated to the physical behaviour of the nitrides. Three main topics will be discussed here: the linear relationship of lattice constants from the molar fraction x of thin AlxGalixN layers, the influence of intentionally and unintentionally incorporated impurities on the electronic properties and the high resolution analyses of thin nitride layers on A120 3 substrates evolving during thermal treatment in 100 mbar NH 3. Such a layer may serve as a buffer layer for the growth of group III nitrides on A120 3 (fig. 1). ELASTIC RECOIL DETECTION (ERD) USING HEAVY ION BEAMS Elastic Recoil Detection (ERD) using energetic heavy ions (fig. 1) is a unique technique to investigate the profiles of light elements in thin films [1, 2, 3]. The samples of interest are irradiated by a heavy ion beam, e.g. 170 MeV 127I, which is delivered in our case by the Munich 15 MV tandem accelerator. The irradiation is performed at small angles of incidence ox which allows a detection of recoil ions, which are scattered at small angles to 745 Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
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