Accurate stoichiometric analysis of polycrystalline indium nitride films with elastic recoil detection

Indium nitride thin films for potential application in high power, high frequency devices have been grown with reactive ion sputtering. Accurate film stoichiometries have been measured with elastic recoil detection using 200 MeV Au projectile ions. The beam-induced depletion of nitrogen during analysis has been found to be severe and non-linear with ion fluence. Assuming the formation of molecular nitrogen as the decisive step leading to nitrogen loss, a model has been applied which reproduces the experimental data. The model allows accurate extrapolations of the original nitrogen content of the material. All films studied have been found to be nitrogen-rich and have large band gaps ranging from 2.14 to 2.3 eV. The amount of excess nitrogen correlates with the band gap energy suggesting a Moss-Burstein effect. The excess nitrogen may thus act as donor and account for the high charge carrier concentrations of up to 2 × 10²⁰ cm^-3. The magnitude of the nitrogen excess is consistent with a donor level 50 meV below the conduction band.